Topic 1: Chapt 1-5 Flashcards

Question

what is a xenobiotic?

Answer 1

Any foreign substance in the body

Answer 2

-Use mass flow to follow material throughout the body. Mass flow describes the rate of transport of a substance x as is moves through the body fluids or into and out of the body. -Mass flow (amount x/min) = (concentration of x) X (volume flow) -where volume flow describes the flow of blood, air, urine, and the like.

Answer 3

-follow the rate at which the substance disappears from the blood -usually expressed as a volume of blood "cleared" of a substance x per unit of time -for this reason, clearance is only an indirect measure of how substance x is handled by the body

Answer 4

-kidney and liver -hepatocytes, or liver cells, metabolise many different types of molecules, especially xenobiotics such as drugs. The resulting metabolites may be secreted into the intestine for excretion in the faeces or released into the blood for removal by the kidneys

Answer 5

-plasma, the fluid component -plus the heavier blood cells

Answer 6

-in a state of homeostasis, the composition of both body compartments is relatively stable -this condition is a dynamic steady state -the modifier dynamic indicates that materials are constantly moving back and forth between two compartments -in a steady state, there is no "net" movement of materials between the compartments

Answer 7

-implies that the composition of the body compartments is identical

Answer 8

has concentration differences, the fluid compartments are not at equilibrium

Answer 9

-human body monitors certain key functions, such as BP and blood glucose concentration, that must stay within a particular operating range if the body is to remain healthy -these important "regulated variables" are kept within their acceptable (normal) range by physiological control mechanisms that kick in if the variable ever strays too far from its "setpoint", or optimum value. - there are two basic patterns of control mechanisms: local control and long-distance reflex control

Answer 10

1. an input signal 2. a control or integrating centre, that regulates incoming information and initiates an appropriate response 3. An output signal that creates a response

Answer 11

-simplest form of control -restricted to the tissue or cell involved -a relatively isolated change occurs in a tissue -a nearby cell or group of cells senses the change in their immediate vicinity and responds, usually by releasing a chemical -the response is restricted to the region where the change took place, hence "local control"

Answer 12

-changes that are widespread throughout the body, or "systemic" in nature, require more complex control systems to maintain homeostasis -e.g., maintaining blood pressure to drive blood flow throughout the body is a systemic issue rather than a local one. Because blood pressure is body-wide, maintaining it require long-distance communication and coordination -reflex control --> mean any long-distance pathway that uses the nervous system, endocrine system, or both

Answer 13

two parts: -a response loop -a feedback loop

Answer 14

3 primary parts: -an input signal -an integrating centre -an output signal

Answer 15

Stimulus--> Sensor --> input signal --> integrating centre --> output signal --> target --> response

Answer 16

-the input side of the response loop starts with a stimulus --> the change occurs when the regulated variable moves out of its desirable range -a specialised sensor monitors the variable. If the sensor is activated by the stimulus, it sends an input signal to the integrating centre. -the integrating centre evaluates the information coming from the sensor and initiates an output signal -the output signal directs a target to carry out a response. If successful, the response brings the regulated variable back into the desired range -In mammals, integrating centres are usually part of the nervous system or endocrine system. -output signals may be chemical, electrical, or a combination. -The targets activated by output signals can be any cell of the body

Answer 17

-designed to keep the system at or near a setpoint so that the regulated variable is relatively stable -the end result is a regulated variable that oscillates around a setpoint

Answer 18

the sensitivity of the system

Answer 19

-a pathway in which the response opposes or removes the signal -negative feedback loops stabilise the regulated variable and thus aid the system in maintaining homeostasis -negative feedback loops can restore the normal state but cannot prevent the initial disturbance

Answer 20

positive feedback loop

Answer 21

-not homeostatic -the response reinforces the stimulus rather than decreasing or removing it -the response sends regulated variable even farther from its normal value -this initiates a vicious cycle of ever-increasing response and sends the system temporarily out of control -because it escalates the response, this type of feedback requires some intervention or event outside the loop to stop the response

Answer 22

-enables the body to predict change about to occur and start the response loop in anticipation of the change -e.g., salivation reflex, the sight, smell, and thought of food enough to start out mouths watering in expectation of eating food

Answer 23

-Regulated variables that change predictably and create repeating patterns or cycles of change are called biological rhythms -the timing of many biorhythms coincides with predictable environmental change, such as daily light-dark cycles or seasons -biological rhythms reflect changes in the setpoint of the regulated variable

Answer 24

-humans have circadian rhythms for many body functions, including BP, BT, and metabolic processes -body temp peaks in the late afternoon and declines dramatically in the early hours of the morning -many hormones in humans have blood concentrations that fluctuate predictably in a 24-hour cycle. Cortisol, growth hormone and sex hormones (most notes e.g.) --> cortisol concentration in a 9:00am sample might be nearly twice as high as one taken in the early afternoon -circadian rhythms cued by the light-dark cycle may correspond to rest-activity cycle. -these rhythms allow our bodies to anticipate behaviour and coordinate body processes accordingly

Answer 25

-biological rhythms create an anticipatory response to a predictable environmental variable

Answer 26

-The adaption of physiological processes to a given set of environmental conditions is known as acclimatization when it occurs naturally -if the process takes place artificially in a laboratory setting, it is called acclimation

Answer 27

-a logical guess about how events take place -they test their hypotheses by designing experiments to collect evidence that supports or disproves their hypotheses, and they publish the results of their experiments in the scientific literature

Answer 28

observation and experimentation

Answer 29

-either removing or altering some variable that the investigator thinks is an essential part of the observed phenomenon

Answer 30

the independent variable - the manipulated element - is the cause - its value is independent of other varibles in the study

Answer 31

- The dependent variable is the effect of the independent variable -- this is the element that is expected to be affected by changing the independent variable

Answer 32

-a control group is usually a duplicate of the experimental group in every respect except that the independent variable is not changed from its initial value - the purpose of the control is to ensure that any observed changes are due to the manipulated variable and not to changes in some other variable

Answer 33

-information, or data, about the effect that the manipulated (independent) variable has on the observed (dependent) variable -once there is enough information to draw a conclusion, begin analysing data -

Answer 34

-repeated to ensure that the results were not an unusual one-time event --> this step is called replication

Answer 35

The hypothesis may become a working model

Answer 36

scientific theory

Answer 37

-human populations have tremendous genetic and environmental variability -there are average values for many physiological variables, such as BP, these values simply represent a number that falls somewhere near the middle of a wide range of values -to show significant differences between experimental and control groups in human experiment, an investigator would have to include a large number of identical subjects -but getting two groups who are identical in every respect is impossible. instead must attempt to recruit similar in as many aspects as possible.

Answer 38

-do a crossover study - in a crossover study each individual acts both as experimental subject and a control -thus, each individual's response to treatment can be compared with their own control value (particularly effective when there is a wide variability within population)

Answer 39

-placebo effect --> give someone a pill and tell the person that it will help alleviate some problem, and there is a strong possibility that the pill will have exactly that effect, even if it contains only sugar or inert substance -nocebo effect --> if you warn people that a drug they are taking may have specific adverse side effects, those people will report a higher incidence of the side effects than a similar group of people who were not warned

Answer 40

-simplest way is with a blind study, in which the subjects do not know whether they are receiving the treatment or the placebo -double-blind studies are better, a third party, not involved in the experiment, is the only one who knows which group is receiving the experimental and placebo treatment -most sophisticated experimental design for minimising psychological effects is the double-blind crossover study --> control group in the first half becomes experimental group in second half, but no one involved knows who is taking the active treatment

Answer 41

-designed to be carried out for a long period of time - a prospective cohort study is a longitudinal study where same participants are followed over a period of time - a retrospective study is a longitudinal study where some or all cases of disease have already occurred before investigator initiates the study --> match groups of people who all have a particular disease to a similar but healthy control group

Answer 42

-survey a population for the prevalence of a disease or condition. -Data from cross-sectional studies identify trends to be investigated further

Answer 43

-attempt to resolve contradictory results of data -combines all data from a group of similar studies and uses sophisticated statistical techniques to extract significant trends or findings from the combined data

Answer 44

oxygen, carbon, and hydrogen

Answer 45

-molecules that contain carbon

Answer 46

-organic molecules associated with living organisms.

Answer 47

4 major groups: -carbohydrates -lipids -proteins -nucleotides

Answer 48

-carbohydrates, lipids, and proteins --> also used as building blocks of cellular components

Answer 49

-biomolecules that play an important role in energy and information transfer -single nucleotides include energy-transferring compounds ATP (adenosine triphosphate) and ADP (adenosine diphosphate), as well as cyclic AMP, a molecule important in the transfer of signals between cells -nucleic acids (or nucleotide polymers) such as RNA and DNA store and transmit genetic information -single nucleotide molecules have two critical functions in the human body: (1) capture and transfer energy in high-energy electrons or phosphate bonds, and (2) aid in cell-to-cell communication

Answer 50

-mostly carbon and hydrogen. Most lipids have a backbone of glycerol and 1-3 fatty acids -important characteristic of lipids is they are nonpolar and therefore not very soluble in water -divided into two broad categories: -fats -->solid at room temperature. most fats are derived from animal sources -Oils --> liquid at room temperature. Most plant lipids are oils

Answer 51

carbon, hydrogen, and oxygen in the ratio CH2O

Answer 52

-nitrogen in addition to carbon, hydrogen, and oxygen - two amino acids also contain sulphur

Answer 53

-protein molecules combined with another kind of biomolecule

Answer 54

-proteins combine with lipids -lipoproteins are found in cell membranes and in the blood, where they act as carriers for less soluble molecules, such as cholesterol

Answer 55

glycosylated molecules are molecules to which a carbohydrate has been attached to

Answer 56

proteins combined with carbohydrates

Answer 57

lipids bound to carbohydrates

Answer 58

cell membranes

Answer 59

-large molecules made up of repeating unit

Answer 60

-fatty acids are long chains of carbon atoms bound to hydrogens, with carboxyl (-COOH) or "acid" group at one end of the chain -saturated fatty acids have no double bonds between carbons, so they are "saturated" with hydrogens. The more saturated a fatty acid is, the more likely it is to be solid at room temperature. -monounsaturated fatty acids have one double bond between two of the carbons in the chain. For each double bond, the molecule has two fewer hydrogen atoms attached to the carbon chain. -polyunsaturated fatty acids have two or more double bonds between carbons in the chain

Answer 61

-Glycerol is a simple 3-carbon molecule that makes up the backbone of most lipids -Monoglyceride --> Glycerol plus one fatty acid -Diglyceride --> Glycerol plus two fatty acids -triglyceride --> Glycerol plus three fatty acids (aka triacylglycerol). More than 90% of lipids are in the form of triglycerides

Answer 62

-Eicosanoids --> modified 20-carbon fatty acids with a complete or partial carbon ring at one end and two long carbon chain "tails". Eicosanoids, such as thromboxanes, leukotrienes, and prostaglandins, act as regulators of physiological functions -steroids --> lipid related molecules whose structure includes four linked carbon rings. Cholesterol is the primary source of steroids in the human body -phospholipids --> have 2 fatty acids and a phosphate group (H2PO4). Cholesterol and phospholipids are important components of animal cell membranes

Answer 63

-most abundant biomolecules -name from their structure, carbon (carbo-) with water (hydro) -general formula for a carbohydrate is (CH₂O)ₙ or CₙH₂ₙOₙ --> showing that for each carbon there are two hydrogens and one oxygen. -divided into three categories: -monosaccharides -disaccharides -polysaccharides

Answer 64

-simple sugars -the most common monosaccharides are the building blocks of complex carbohydrates and have either five carbons, like ribose, or six carbons like glucose

Answer 65

-consist of glucose plus another monosaccharide

Answer 66

-glucose polymers. All living cells store glucose for energy in the form of polysaccharide

Answer 67

-polymers of smaller building-block molecules called amino acids

Answer 68

Primary structure: -The 20 protein-forming amino acids assemble into polymers called peptides. The sequence of amino acids into a peptide chain is called the primary structure. The 20 amino acids can create almost infinite number of combinations -peptides range in lengths from two to two million amino acids: --Oligopeptide: 2-9 aminos acids --polypeptides: 10-100 amino acids --proteins: > 100 amino acids Secondary Structure: -secondary structure is created primarily by hydrogen bonds between adjacent chains or loops -covalent bond angles between amino acids determine secondary structure Tertiary structure: -is the protein's three-dimensional shape -can be a mix of secondary structures. Beta-sheets are shown as flat ribbon arrows and alpha helices are shown as ribbons coils Quaternary structure: -Multiple subunits combine with noncovalent bonds. Haemoglobin molecules are made from four globular protein subunits

Answer 69

-all amino acids have a carboxyl (-COOH), an amino group (-NH₂), and a hydrogen attached to the same carbon. The fourth bond of the carbon attaches to a variable "R" group -The nitrogen (N) in the amino group makes proteins our major dietary source of nitrogen -The R groups differ in their size, shape, and ability to form hydrogen bonds or ions. Because of the different R groups, each amino acid reacts with other molecules in a unique way -in a peptide bond, the amino group of one amino acid joins the carboxyl group of the other, with the loss of water -20 amino acids commonly occur in natural proteins. The human body can synthesize most of them, but at different stages of like some amino acids must be obtained from diet and are therefore considered essential amino acids -a few amino acids do not occur in proteins but have physiological functions --homocysteine: a sulphur-containing amino acid that in excess is associated with heart disease --gamma-amino butyric acid (gamma-amino butyric acid) or GABA: a chemical made by nerve cells --Creatine: a molecule that store energy when it binds to a phosphate group

Answer 70

-some combinations of elements that occur repeatedly in biological molecules -atoms in a functional group tend to move from molecule to molecule as a single unit

Answer 71

-phosphorylation is the addition of a phosphate group -dephosphorylation is the removal of a phosphate group phosphate group - H2PO4

Answer 72

amino - NH2 Carboxyl (acid) - COOH Hydroxyl - OH phosphate - H2PO4

Answer 73

-the arrangement of electrons in the outer energy level (shell) of an atom determines an element's ability to bind with other elements. Electrons shared between atoms form strong covalent bonds that bind atoms together to form molecules -molecules form when atoms share pair of electrons, one electron from each atom, to create covalent bonds -these strong bonds require the input of energy to break them apart -if adjacent atoms share two pair of electrons rather than just one pair, a double bond, represented by a double line, results. If two atoms share three pairs of electrons, they form triple bond

Answer 74

-if an atom or molecule gains or loses one or more electrons, it acquires an electrical charge and becomes an ion. Ions are the basis for electrical signalling in the body. -cations are positively charged -anions are negatively charged -important ions of the body are: Sodium - NA+ potassium - K+ calcium - Ca2+ Hydrogen - H+ Magnesium - Mg2+ Chloride - Cl- Bicarbonate - HCO3- phosphate - HPO4(2-) sulphate - SO4(2-)

Answer 75

-the electrons in certain atoms can capture energy from their environment and transfer it to other atoms. This allows the energy to be used synthesis, movement, and other life processes. The released energy may also be emitted as radiation. e.g., bioluminescence in fireflies is visible light emitted by high-energy electrons returning to their normal low-energy state.

Answer 76

-are unstable molecules with an unpaired electron. -they are thought to contribute to aging and to the development of certain diseases, such as some cancers

Answer 77

-covalent and ionic bonds are strong, because they require a lot of energy to make or break -hydrogen bond and van der Walls forces are weaker bonds that require much less energy to break

Answer 78

-ribonucleic acid is a single-strand nucleic avid with ribose as the sugar in the backbone, and four bases - adenine, guanine, cytosine, and uracil

Answer 79

-deoxyribonucleic acid is a double helix, a three-dimensional structure that forms when two DNA stands link through hydrogen bonds between complementary base pair. Deoxyribose is the sugar in the backbone, and the four bases are adenine, guanine, cytosine, and thymine

Answer 80

bases on one strand form hydrogen bonds with bases on the adjoining strand. This bond follows very specific rule: -Because purines are larger than pyrimidine, space limitation always pair a purine with a pyrimidine -Guanine (G) forms three hydrogen bonds with cytosine (C) -Adenine (A) forms two hydrogen bonds with thymine (T) or uracil (U) more energy is require to break the triple hydrogen bonds of G and C then the double bonds of A and T or A and U

Answer 81

-determine the element (atomic number)

Answer 82

the isotope

Answer 83

protons + neutrons in nucleus

Answer 84

-from covalent bonds -create ions when gained or lost -capture and store energy -create free radicals

Answer 85

-some molecules develop regions of partial positive and negative charge when the electron pairs in their covalent bonds are not evenly share between the linked atoms. When electrons are shares unevenly; the atom(s) with the stronger attraction for electrons develop a slight negative charge (indicated by δ+ (delta)) and the atom(s) with the weaker attraction for electrons develops a slight positive charge (δ−). These molecules are called polar molecules, because they can be said to have positive and negative ends, or poles -polarity makes good solvents

Answer 86

-is one whose share electrons are distributed so evenly that there are no regions of partial positive or negative charge

Answer 87

-ionic bonds, hydrogen bonds, and van der Waals forces (all noncovalent bonds)

Answer 88

-aka electrostatic attractions -results from attraction between ions with opposite charges

Answer 89

-a weak attractive force between hydrogen atom and a nearby oxygen, nitrogen, or fluorine atom - no electrons are gained, lost, or shared in a hydrogen bond -oppositely charged regions in polar molecules are attracted to each other. hydrogen bonds may occur between atoms in neighbouring molecules or between atoms in different parts of the same molecule

Answer 90

-hydrogen bonding between molecules is responsible for surface tension of water -surface tension is the attractive force between water molecules that causes water to form spherical droplets when falling or to bead up when spilled onto a non-absorbent surface. The high cohesiveness of water is due to hydrogen bonding and makes it difficult to stretch or deform

Answer 91

-are weak, nonspecific attractions between the nucleus of any atom and the electrons of nearby atoms. Two atoms that are weakly attracted to each other by wan der Waals forces move closer together until they are close that their electrons begin to repel one another, van der Wassl forces allow atoms to pack closely together and occupy a minimum amount of space. A single wan der Waals attraction between atoms is very weak

Answer 92

The degree to which a molecule is able to dissolve in a solvent, the more easily a molecule dissolves, the higher its solubility

Answer 93

nonpolar molecules, lipids (fats and oils) are the most hydrophobic group of bioloigcal molecules

Answer 94

-The A-helix (alpha-helix) spiral -The zigzag shape of B-sheets (beta-sheets) -adjacent B-strands in the polypeptide chain associate into sheetlike structure held together by hydrogen bonding, shown as dotted lines (. . .) -the sheet configuration is very stable and occurs in many proteins destined for structural uses -proteins with other functions may have a mix B-strands and A-helices

Answer 95

covalent bond angles and weak non-covalent interactions within a molecule

Answer 96

covalent bond angles between amino acids in the polypeptide chain

Answer 97

spontaneous folding as the result of covalent bonds and noncovalent interactions

Answer 98

-into two large groups based on their shape: -Globular proteins -fibrous proteins

Answer 99

-can be a mix of A-helices, B-sheets, and amino acid chains that fold back on themselves -the result is a complex tertiary structure that may contain pockets, channels, or protruding knobs -the tertiary structure of globular proteins arises partly from the angles of covalent bonds between amino acids and partly from the hydrogen bonds, van der Waals forces, and ionic bonds that stabilise the molecule's shape -in addition to covalent bonds between adjacent amino acids covalent disulphide (S-S) bonds play an important role in the shape of many globular proteins --> amino acid cysteine contains sulphur as part of a sulfhydryl group (-SH). Two cysteines in different parts of the polypeptides chain can bond to each other with a disulfide bond that pulls the sections of chain together

Answer 100

-can be B-strands or long chains of A-helices -are usually insoluble in water and form important structural components of cells and tissues -examples of fibrous proteins include collagen, found in many types of connective tissues, such as skin, and keratin, found in hair and nails

Answer 101

can change. A change in shape may alter or destroy the molecule's ability to function

Answer 102

the concentration of free H+ in body fluids, measures in terms of pH

Answer 103

-some come from separation of water molecules (H2O) into H+ and OH- ions -others come from acids (molecules that release H+) when they dissolve in water

Answer 104

true, when the hydrogen is part of the intact acid molecule (e.g., carbonic acid), it does not contribute to acidity.

Answer 105

-body maintains normal pH using buffers -a buffer is any substance that moderate changes in pH -many buffers contain anions that have a strong attraction to H+ molecules. When free H+ is added to a buffer solution, the buffer's anions bond to the H+, thereby minimizing any change in pH

Answer 106

-any substance that dissolves in a liquid. The degree to which a molecule is able to dissolve in a solvent is the molecule solubility. The more easily a solute dissolve, the higher its solubility

Answer 107

-the liquid into which solutes dissolve. In biological solutions, water is the universal solvent

Answer 108

-a solution is the combination of solutes dissolved in a solvent. The concentration of a solution is the amount of solute per unit volume of solution -concentration = solute amount/ volume of solution

Answer 109

-calculated from the chemical formular of a molecule. This is the mass of one molecule, expressed in atomic mass units (amu) or, more often, in Daltons (Da), where 1 amu = 1 Da -molecular mass = SUM [(atomic mass of each element) x (the number of atoms of each element)]

Answer 110

-Moles (mol) are an expression of the number of solute molecules, without regard for their weight. -one mole = 6.02 x 10^23 atoms, ions, or molecules of a substance -one mole of a substance has the same number of particles as one mole of any other substance

Answer 111

-in the laboratory, we use the molecular mass of a substance to measure out moles -e.g., one mole of glucose (with 6.02 x 10^23 glucose molecules) has a molecular mass of 180 Da and weighs 180 grams. The molecular mass of a substance expressed in grams is called the gram molecular weight.

Answer 112

-are a unit used for ions, where 1 Eq = molarity of the ion x the number of charges the ions carries -e.g., sodium ion, with its charged of +1, has one equivalent per mole -the hydrogen phosphate (HPO4(2-)) has two equivalents per mole -concentration of ions in the blood are often reported in milliequivalents per litre (mEq/L)

Answer 113

-in lab, scientists cannot measure out solutes by the mole. They use the more conventional measurement of weight. The solute concentration may then be expressed as a percentage of the total solution, or percent solution. -A 10% solution means 10 parts of a solute per 100 part of total solution -Weight/volume solutions, used for solutes that are solids, are usually expressed as g/100 mL solution or mg/dL -out of date way of expressing mg/dL is mg% where % means per 100 parts or 100 mL (20mg/dL = 20 mg%

Answer 114

-is the number of moles of solute in a litre of solution, and is abbreviated as either mol/L or M. -A one molar solution of glucose (1 mol/L, 1 M) contains 6.02 x 10^23 molecules of glucose per litre of solution -it is made by dissolving one mole (180 grams) of glucose in enough water to make one litre per solution -typical biological solutions are so dilute that solute concentrations are usually expressed as millimoles per litre (mmol/L or mM)

Answer 115

-molecules that have polar regions or ionic bonds readily interact with the polar regions of water. This enables them to dissolve easily in water. Molecules that dissolve readily in water are said to be hydrophilic (hydro-, water + philos, loving)

Answer 116

-Because they have an even distribution of electrons and no positive or negative poles, nonpolar molecules have no regions of partial charge, and therefore tend to repel water molecules. -molecules like these do not dissolve readily in water and are said to be hydrophobic (hydro- water, + phobos, fear). -molecules such as phospholipids have both polar and nonpolar regions that play critical roles in biological systems in the formation of biological membrane

Answer 117

-a molecule that contributes H+ to a solution -carboxyl group, -COOH, is an acid because in solution it tends to lose its H+ -acidic solutions have gained H+ from an acid and have a pH less than 7

Answer 118

-a molecule that decreases the H+ concentration of a solution by combining with free H+ -molecules that produce hydroxide ions, OH-, in solution are bases because the hydroxide combines with H+ to form water -basic or alkaline solutions have a H+ concentration lower than that of pure water and have a pH value greater than 7

Answer 119

-concentration of H+ in body fluids is measured in terms of pH -the expression of pH stands for "power of hydrogen" -pH = -log[H+] ----> This equation is read as "pH is equal to the negative log of the hydrogen ion concentration." -[] by convention expressed in mEq/L -Using the rule of logarithms that says -log x = log (1/x), pH equation can be rewritten as: pH= log(1/[H+]) ----> as [H+) goes up, pH goes down -pH of a solution is measures on a numeric scale between 0 and 14. The pH scale is logarithmic, meaning that a change in pH value of 1 unit indicates a 10-fold change in [H+]. e.g., if a solution changes from pH 8 to pH 6, there has been a 100-fold (10^2) increase in [H+] -The normal pH of blood in the human body is 7.40. Homeostatic regulation is critical because blood pH less than 7.00 or greater than 7.70 is incompatible with life

Answer 120

Fall into seven broad categories: -Enzymes -- Some proteins act as enzymes, biological catalysts that speed up chemical reactions. Enzymes play an important role in metabolism -Membrane transporters -- proteins in cell membranes help move substances back and forth between the intracellular and extracellular compartments. These proteins may form channels in the membrane, or they may bind to molecules and carry them through the membrane -Signal molecules -- some protein and smaller peptides act ass hormones and other signal molecules -Receptors -- proteins that bind signal molecules and initiate cellular responses are called receptors -Binding proteins -- These proteins, found mostly in the extracellular fluid, bind and transport molecules throughout the body. Examples you have already encountered include the oxygen-transporting protein haemoglobin and the cholesterol-binding proteins, such as LDL (low density lipoprotein -Immunoglobins -- These extracellular immune proteins, also called antibodies, help protect the body from foreign invaders and substance -Regulatory proteins -- turn cell processes on and off or up and down. E.g., the regulatory proteins known as transcription factors bind to DNA and alter gene expression and protein synthesis

Answer 121

-specificity -affinity -competition -saturation

Answer 122

any molecule or ions that binds to another molecule

Answer 123

ligands that bind to enzymes and membrane transporters as also called substrates

Answer 124

-The ability of a protein to bind to a certain ligand or a group of related ligands -Some proteins specific about the ligands they bind to, others bind to whole groups of molecules -ligand binding require molecular complementarity -the ligand and the protein binding site must be complementary -when ligand and protein come close to each other, noncovalent interactions between the ligand and the protein's binding site allow the two molecules to bind -protein's binding site and shape of its ligand do not need to fit one another exactly -When binding site and ligand come close to each other, the begin to interact through hydrogen and ionic bonds and van der Waals forces -the protein's binding site then changes shape (conformation) to fit more closely to the ligand --> this is the induced-fit model

Answer 125

-the degree to which a protein is attracted to a ligand is called the protein's affinity for the ligand -high affinity = more likely to bind -binding is reversible -reversible binding reactions go to a state of equilibrium, where the rate of binding (P + L --> PL) is exactly equal to the rate of unbinding, or dissociation (P + L <-- PL) -when a reaction is at equilibrium, the ratio of the product concentration, or protein-ligand complex [PL], to the reactant concentrations [P][L] is always the same - this ratio is called the equilibrium constant Keq, appears to all reversible chemical reactions Keq = [PL] / [P][L] -the higher the affinity the larger the Keq

Answer 126

- the equilibrium is disrupted when more protein or ligand is added to the system. Now the ratio of [PL] to [P][L] differs from the Keq -in response, the rate of the binding reaction increases to convert some of the added P or L into the bound protein-ligand complex -As the ratio approaches its equilibrium value again, the rate of the forward reaction slows down until finally the system reaches the equilibrium ration once more --> [P], [L], and [PL} have all increased over their initial value, but the equilibrium ratio has been restored ------> this situation describe is example of a reversible reaction obeying the law of mass action

Answer 127

-when a reaction is at equilibrium, the ratio of the products to the substrates is always the same -if the ratio is disrupted by adding or removing one of the participants, the reaction equation will shift direction to retore the equilibrium condition

Answer 128

-Kd = [P][L]/[PL] -reciprocal of the equilibrium constant -large Kd indicates the low binding affinity of the protein for the ligand, with more P and L remaining in the unbound site. Conversely, small Kd means higher value for [PL] relative to [P] and [L], so a small Kd indicates higher affinity of the protein for the ligand - if one protein binds to several related ligands, a comparison of the Kd values can tell us which ligand is more likely to bind to the protein.

Answer 129

- the related ligands that compete for the binding sites are called competitors -competition between ligands is a universal property of protein binding

Answer 130

-competing ligands that mimic each other's actions -may occur in natures, such as nicotine, which mimics the activity of acetylcholine by binding to the same receptor. Can also be synthesized.

Answer 131

-no, chemical and physical factors can alter, or modulate, binding affinity or even totally eliminate it

Answer 132

-closely related proteins whose function is similar but whose affinity for ligands differs are called isoforms of one another

Answer 133

-also known as proteolytic activation -some proteins are inactive when they are synthesized in the cell -before such a protein can become active, enzymes must chop off one or more portions of the molecule -the activation of some proteins requires the presence of a cofactor, which is an ion or small organic functional group --> cofactors must attack to the protein before the binding site will become active and bind a ligand

Answer 134

A factor the influences either protein binding or protein activity is called a modulator

Answer 135

the modulator either (1) changes the protein's ability to bind to the ligand or it (2) changes the protein's activity or its ability to create a response

Answer 136

-molecules that bind covalently or noncovalently to proteins and alter their binding ability or their activity -may activate or enhance ligand binding, decrease binding ability, or completely inactivate the protein so that it is unable to bind any ligand -inactivation may be either reversible or irreversible -antagonists, also called inhibitors, are chemical modulators that bind to a protein and decrease its activity.

Answer 137

-competitive inhibitor -irreversible inhibitor -allosteric modulator -covalent modulator -pH and temperature

Answer 138

-reversible antagonists that compete with the customary ligand for the binding site -the degree of inhibit depends on the relative concentrations of the competitive inhibitors and the customary ligand, as well as the protein's affinities for the two -The binding of competitive inhibitors is reversible: increasing the concentration of the customary ligand can displace the competitive inhibitor and decrease the inhibition

Answer 139

-Bind tightly to the protein and cannot be displaced by competition -Antagonist drugs have proven useful for treating many conditions -e.g., tamoxifen, an antagonist to the oestrogen receptor, is used in treatment of hormone-dependent cancers of the breast

Answer 140

-may be either antagonists or activators -bind reversibly to a protein at a regulatory site away from the binding site, and by doing so change the shape of the binding site -allosteric inhibitors are antagonists that decrease the affinity of the binding site for the ligand and inhibit protein activity. -allosteric activators increase the probability of protein-ligand binding and enhance protein activity

Answer 141

-may be either antagonists or activators -are atoms or functional groups that bind covalently to proteins and alter proteins' properties -like allosteric modulators, covalent modulators may either increase or decrease a protein's binding ability or its activity -e.g., phosphorylation

Answer 142

-temperature and pH (acidity) can have dramatic effects on protein structure and function -small changes in pH or temp act as modulators to increase or decrease activity -however, once these factors exceed some critical value, they disrupt the noncovalent bonds holding the protein in its tertiary conformation, loses its shape and activity ---> when protein loses its conformation its is said to be denatured -in few cases activity can be restored if the original temp and pH returns --> usually denaturation produces a permanent loss of activity

Answer 143

programmed production of new proteins (receptors, enzymes, and membrane transporters

Answer 144

programmed removal of proteins

Answer 145

varies using up-regulation and down-regulation

Answer 146

direct influence on the magnitude of the cell's response, cells alter amount of protein by influencing both its synthesis and breakdown. Even when the amount of protein is constant, there is still a steady turnover of protein molecules

Answer 147

determine the magnitude of the response. Fewer ligands activate fewer proteins, and the response is low. As the ligand concentration increase, so does the magnitude of the response, up to a maximum where all protein binding sites are occupied -- called saturation point

Answer 148

The basic functional unit of living organisms, and an individual cell can carry out all the processes of life

Answer 149

Three major cavities: -Cranial cavity (Skull) - contains the brain -Thoracic cavity (thorax) - bounded by the spine and ribs on top and sides, with muscular diaphragm forming the floor. Contains the heart, which is enclosed in a membranous pericardial sac, and the two lungs, enclosed in separate pleural sac -abdominopelvic cavity - abdomen and pelvis form one continuous cavity. A tissue lining called peritoneum lines the abdomen and surrounds the organs within (stomach, intestines, liver, pancreas, gallbladder, and spleen). Kidney lie outside the abdominal cavity, between the peritoneum and the muscles and bones of the back, just above waist level. pelvis contains reproductive organs, urinary bladder and the terminal portion of the large intestine

Answer 150

-blood-filled vessels and heart of the circulatory system form one compartment -our eyes are hollow fluid filled spheres subdivided into compartments, the aqueous and vitreous humours -The brain and spinal cord are surrounded by a special fluid compartment known as cerebrospinal fluid (CSF). -Membranous sacs that surround the lungs (pleural sacs) and the heart (pericardial sac) also contain small volumes of fluid

Answer 151

-the interior of any hollow organ is called lumen -may be wholly or partially filled with air or fluid

Answer 152

two main fluid compartments: (1) the extracellular fluid (ECF) outside the cells -The ECF subdivides further into: --Plasma, the fluid portion of the blood, and; --Interstitial fluid, which surrounds most cells of the body (2) The intracellular fluid (ICF) within the cells -dividing wall between ECF and ICF is the cell membrane

Answer 153

Has two meanings: -before invention of microscopes in sixteenth century, membrane always describe a tissue that lined a cavity or separated two compartments. -after microscope, can also be applied to cell membrane.

Answer 154

-Physical isolation -Regulation of exchange with the environment -Communication between the cell and its environment -Structural support

Answer 155

-the more metabolically active a membrane is, the more proteins it contains

Answer 156

-peripheral proteins can be removed without disrupting the integrity of the membrane -phospholipid heads face the aqueous intracellular and extracellular compartments -lipid tails form the interior layer of the membrane --> cholesterol molecules insert themselves into the lipid layer -transmembrane proteins cross lipid bilayer -extracellular surface glycoproteins and glycolipids -all cell membranes are of relatively uniform thickness, about 8nm

Answer 157

Three main types: -Phospholipids -Sphingolipids -Cholesterol

Answer 158

-made up of glycerol backbone with two fatty acid chains extending to one side and a phosphate group extending to the other -the glycerol-phosphate head of the molecule is polar and thus hydrophilic -the fatty acid "tail" is nonpolar and thus hydrophobic

Answer 159

-The micelle -the liposome -the phospholipid bilayer

Answer 160

-small droplets with a single layer of phospholipids arranged so that the interior of the micelle is filed with hydrophobic fatty acid tails -important in the digestion and absorption of fats in the digestive tract

Answer 161

-larger spheres with bilayer phospholipid walls -leaves hollow centre with an aqueous core that can be filled with water-soluble molecules -liposome-like structure thought to be precursor of the first living cell -being used as a medium to deliver drugs and cosmetics --> researchers can make immunoliposomes that use antibodies to recognise specific types of cancer cells

Answer 162

-sphingolipids also have fatty acid tails, but their heads may either be phospholipids or glycolipids -slightly longer than phospholipids

Answer 163

-Cholesterol molecules, which are mostly hydrophobic, insert themselves between the hydrophilic heads of phospholipids -helps make membrane impermeable to small water soluble molecules and keep membrane flexible over a wide range of temperatures

Answer 164

-cholesterol -phospholipids, sphingolipids -carbohydrates -proteins -cholesterol, and phospholipids and sphingolipids together form lipid bilayer -phospholipids and sphingolipids, and carbohydrates together form glycoproteins -carbohydrates and proteins together form glycoproteins

Answer 165

-tightly bound to the membrane, and the only way they can be removed is by disturbing the membrane structure with detergents or other harsh methods that destroy the membrane's integrity. Integral proteins include transmembrane proteins and lipid-anchored proteins

Answer 166

-attach to other membrane proteins by noncovalent interactions and can be separated from the membrane by chemical methods that do not disrupt the integrity of the membrane. -peripheral proteins include some enzymes as well as structural binding proteins that anchor the cytoskeleton to the membrane

Answer 167

-Are integral proteins, tightly but not covalently bound to the membrane -The 20-25 amino acids in the protein chain segments that pass through the bilayer are nonpolar. This allows those amino acids to create strong noncovalent interactions with the lipid tails of the membrane phospholipids, holding them tightly in place -also called membrane-spanning proteins because the protein's chains extend all the way across the cell membrane -When protein crosses the membrane more than once, loops of the amino acid chain protrude into the cytoplasm and the extracellular fluid. -Carbohydrates may attach to the extracellular loops, and phosphate groups may attach to the intracellular loops -phosphorylation or dephosphorylation of proteins is one way cells alter protein function -transmembrane proteins are classified into families according to how many transmembrane segments they have --> many physiologically important membrane proteins have seven transmembrane segments, others cross the membrane only once or up to 12 times

Answer 168

-some of these are proteins that are covalently bound to lipid tails that insert themselves into the bilayer - Others, found only on the external surface of the cell, are held by a GPI anchor that consists of a membrane lipid plus a sugar-phosphate chain. (GPI = glycosylphosphatidylinositol) -many lipid-anchored proteins are associated with membrane sphingolipids, leadings to the formation of specialised patches of membrane called lipid rafts. The longer tails of the sphingolipids elevate the lipid rafts over their phospholipid neighbours.

Answer 169

-the original fluid mosaic model of the cell membrane suggests yes, directed by protein fibres that run just under the membrane surface. But recently researchers have learnt this is not true of all membrane proteins - some integral proteins are anchored to cytoskeletal proteins and are immobile - the ability of the cytoskeleton to restrict the movement of integral proteins allows cells to develop polarity, in which different faces of the cell have different proteins and therefore different properties

Answer 170

-most membrane carbohydrates are sugars attached either to membrane proteins (glycoproteins) or to membrane lipids (glycolipids). -they are found exclusively on the external of the surface of cell, where they form a protective layer known as the glycocalyx

Answer 171

become active, transforming the cell into a specialised unit.

Answer 172

-all material inside the cell membrane except for the nucleus, has four components: --Cytosol or intracellular fluid: The cytosol is a semi-gelatinous fluid separated from the extracellular fluid by the cell membrane. Cytosol contains dissolved nutrients and proteins, ions, and waste products. The other components of the cytoplasm - inclusions, fibres, and organelles - suspended in the cytosol --inclusions: particles of insoluble materials. Some are nutrients. Others are responsible for specific cell functions. These structures are sometimes called the non-membranous organelles --insoluble protein fibres from the cell's internal support system, or cytoskeleton --Organelles - "little organs": Are membrane-bound compartments that play specific roles in the overall function of the cell. Work in an integrated manner, each organelle taking on one or more of the cell's functions

Answer 173

-do not have boundary membranes so in direct contact with the cytosol -movement of material between inclusions and cytosol does not require transport across a membrane -nutrients are stored as glycogen granules and lipid droplets. -Most inclusions with functions other than nutrients storage are made from protein or combination of RNA and protein

Answer 174

-small, dense granules of RNA and protein that manufacture proteins under the direction of cell's DNA -fixed ribosomes attach to the cytosolic surface of organelles -free ribosomes are suspended free in the cytosol -some free ribosomes from groups of 10-20 known as polyribosomes -a ribosome that is fixed one minutes may release and become a free ribosome the next -ribosomes are most numerous in cells that synthesize proteins for export out of the cell

Answer 175

-actin fibres: thinnest, aka microfilaments - 7nm - made form actin (globular) protein - associates with myosin for muscle contraction ---microvilli are finger like extensions that increase cell surface area for absorption of materials. They are supported by microfilaments. -intermediate filaments (neurofilament in nerve cells) - 10 nm - made from keratin, neurofilaments protein (filaments) - hair and nails, protective barrier of skin -microtubules: largest protein fibres, are hollow - 25 nm - made of protein called tubulin (globular) - movement of cilia, flagella, and chromosomes; intracellular transport of organelles -large number of accessory proteins are associated with the cell's protein fibres

Answer 176

two general properties: -structural support comes primarily from the cytoskeleton -movement of the cell or of elements within the cell takes place with the aid of protein fibres and a group of specialised enzymes called motor proteins

Answer 177

-centrioles, cilia, and flagella. These are involved in some form of cell movement

Answer 178

- The cell's microtubule-organising centre, the centrosome, assembles tubulin molecules into microtubules - Centrosome appears as a region of darkly staining material close to the cell nucleus. In most animal cells, the centrosome contains two centrioles

Answer 179

-each centriole is a cylindrical bundle of 27 microtubules, arranged in nine triplets -in cell division, the centrioles direct movement of DNA strands. -cells that have lost their ability to undergo cell division, such as mature nerve cells, lack centrioles

Answer 180

-short, hairlike structures projecting from the cell surface like bristles of a brush -most cells have a single short cilium, but cells lining the upper airways and part of the female reproductive tract are covered with cilia -in these tissues, coordinated ciliary movement create currents that sweep fluids or secretions across the cell surface -the surface of a cilium is a continuation of the cell membrane. The core of motile, or moving, cilia contains nine pairs of microtubules surrounding a central pair -the microtubules terminate just inside the cell at the basal body -These cilia beat rhythmically back and forth when the microtubules pairs in their core slide past each other with the help of the motor protein dynein

Answer 181

-have the same microtubule arrangement as cilia but considerably longer -are found on free-floating single cells, and in humans the only flagellated cell is the male sperm cell -a sperm cell has only one flagellum, in contrast to ciliated cells, which may have one surface almost totally covered with cilia -the wavelike movements of the flagellum push the sperm through fluid, just as undulating contractions of a snake's body push it headfirst through the environment. -Flagella bend and move by the same basic mechanism as cilia

Answer 182

-the cytoskeleton is a flexible, changeable three-dimensional scaffolding of actin microfilaments, intermediate filaments, and microtubules that extends throughout the cytoplasm -some cytoskeleton protein fibres are permanent, but most are synthesised or disassembled according to the cell's needs

Answer 183

Has at least five important functions: -cell shape -internal organisation -intracellular transport -assembly of cells into tissues -movement

Answer 184

-Are proteins that convert stored energy into directed movement -Three groups of motor proteins are associated with the cytoskeleton: myosins, kinesins, and dyneins -all three groups use energy stored in ATP to propel themselves along cytoskeleton fibres -most motor proteins are made of multiple protein chains arranged into three parts: two heads that bind to the cytoskeleton fibre, a neck, and a tail region that is able to bind "cargo" such as an organelle that needs to be transported through the cytoplasm -the heads alternatively bind to the cytoskeleton fibre, then release the "step" forward using the energy stored in ATP -myosins bind to actin fibres and are best known for their role in muscle contraction -Kinesins and dyneins assist the movement of vesicles along microtubules. Dyneins also associated with the microtubule bundles of cilia and flagella to help create their whiplike motion

Answer 185

-have double wall that creates two separate compartments within the mitochondrion -in the centre, inside the inner membrane, is the compartment called the mitochondrial matrix -The matrix contains enzymes, ribosomes, granules, and its own DNA. -this mitochondrial DNA has a different nucleotide sequence from that found in the nucleus -because mitochondria have their own DNA, they can manufacture some of their own proteins - the second compartment inside the mitochondrion is the intermembrane space, which lies between the outer and inner mitochondrial membranes --> plays important role in mitochondrial ATP production, so number of mitochondria in cell is directly related to the cell's energy needs --> e.g., skeletal muscle cells have more mitochondria than adipose cells -mitochondria can replicate themselves even when the cell they belong to is not undergoing cell division --> aided by the mitochondrial DNA, which allows the organelles to direct their own duplication ---> replicate by budding, during which small daughter mitochondria pinch off from an enlarged parent

Answer 186

-according to prokaryotic endosymbiont theory, mitochondria is the descendant of bacteria that invaded cells millions of years ago. The bacteria developed a mutually beneficial relationship with their hosts and soon became an integral part of the host cells --> supporting evidence for this theory is the fact that our mitochondrial DNA, RNA, and enzymes are similar to those in bacteria but unlike those in our own cell nuclei.

Answer 187

-is a network of interconnected membrane tubes with three major functions: synthesis, storage, and transport of biomolecules -two forms of ER: rough ER (RER) and smooth ER (SER) -RER is the main site of protein synthesis. Proteins are assembled on ribosomes attached to the cytoplasmic surface of RER, then inserted into the ERE lumen, where they undergo chemical modification -SER lacks attached ribosomes and is the main site for the synthesis of fatty acids, steroids, and lipids -Phospholipids for the cell membrane are produced here, and cholesterol is modified into steroid hormones, such as the sex hormones oestrogen and testosterone -SER of liver and kidney cells detoxifies or inactivated drugs. In skeletal muscles cells, a modified form of SER stores Ca2+ ions to be used in muscle contraction

Answer 188

-consists of a series of hollow curved sacs, called cisternae, stacked on top of one another, and surrounded by vesicles -receives proteins made on the RER, modifies them, and packages them into vesicles

Answer 189

two kinds: -secretory vesicles, contains proteins that will be released from the cell -storage vesicles, contents of these never leave the cells

Answer 190

-small storage vesicles - appear as membrane-bound granules in the cytoplasm -act as the digestive system of cell, use powerful enzymes to break down bacteria or old organelles, e.g., mitochondria, into their component molecules --> molecules that can be reused reabsorbed into cytosol, while rest are humped out of cell -50 types of enzymes identified from lysosomes of different cell types -lysosomal enzymes are activated only by very acidic conditions, 100 times more acidic than the normal acidity level in cytoplasm --> that's why lysosomal enzymes do not normally destroy the cell that contains them -When lysosomes first pinch off from the Golgi apparatus their interior pH is about the same as the cytosol (7.0-7.3). Enzymes inactive at this pH. Will not harm cell if accidental break occurs ----> as lysosome sits in cytoplasm, accumulates H+ in a process that uses energy. Increasing concentrations of H+ decrease the pH inside the vesicles to 4.8-5.0, and enzymes are activated --> lysosomal enzymes can break down biomolecules inside vesicles --> lysosomal membrane not affected by enzymes -occasionally, lysosomes release enzymes outside the cell to dissolve extracellular support material, such as hard calcium carbonate portion of bone. In other instances cells allow their lysosomal enzymes to come in contact with cytoplasm, leading to self-digestion of all or part of the cell.

Answer 191

-are storage vesicles that are even smaller than lysosomes -main function is degrade long-chain fatty acids and potentially toxic foreign molecules -get their name from the fact that the reactions take place inside them generate hydrogen peroxide (H2O2) a toxic molecule. The peroxisomes rapidly convert this peroxide to oxygen and water using the enzyme catalase. -peroxisomal disorders disrupt the normal processing of lipids and can severely disrupt neural function by altering the structure of nerve cell membranes

Answer 192

-boundary of the nucleus, two-membrane structure that separates the nucleus from the cytoplasmic compartment. Both membranes of the envelope are pierced by round holes or "pores" -communication between nucleus and cytosol occurs through nuclear pore complex, large protein complexes with a central channel -ions and small molecules move freely through this channel when it is open, but transport of large molecules such proteins and RNA is a process that requires energy --> specificity of the transport process allows the cell to restrict DNA to the nucleus and various enzymes to either the cytoplasm or the nucleus

Answer 193

-Nucleus appears filled with randomly scattered granular material, or chromatin, composed of DNA and associated proteins -usually a nucleus also contains from one to four larger dark-staining bodies of DNA, RNA, and protein called nucleoli -nucleoli contain the genes and proteins that control the synthesis of RNA for ribosomes

Answer 194

(1) RNA for protein synthesis is make from DNA (mRNA). mRNA is transcribed from genes in the DNA (2) mRNA leaves the nucleus and attaches to cytosolic ribosomes, initiating protein synthesis (3) some proteins are released by free ribosomes into the cytosol or are targeted to specific organelles (4) ribosomes attached to the RER direct proteins destined for packaging into the lumen of RER (5) Proteins are modified as they pass through the lumen of the ER (6) Transport vesicles move the proteins from the ER to the Golgi apparatus (7) Golgi cisternae migrate toward the cell membrane (8) Some vesicles bud off the cisternae and move in a retrograde or backward fashion (9) some vesicles bud off to form lysosomes or storage vesicles (10) Other vesicles become secretory vesicles that release their content outside the cell

Answer 195

tissues, held together by specialised connections called cell junctions and other support structures

Answer 196

-The study of tissue structure and function

Answer 197

By their physical features: (1) The shape and size od the cells (2) The arrangement of the cells in the tissue (in layers, scattered, etc.) (3) The way cells are connected to one another (4) The amount of extracellular material present in the tissue

Answer 198

Four types: -epithelial -connective -muscle -neural (nerve)

Answer 199

Two basic components: -proteoglycans: Are glycoproteins, which are proteins covalently bound to polysaccharide chains -insoluble protein fibres: such as collagen, fibronectin, and laminin, provide strength and anchor cells to the matrix

Answer 200

-membrane-spanning proteins responsible both for cell junctions and for transient cell adhesion -Cell-cell or cell-matric adhesions mediated by CAMs are essentials for normal growth and development. -e.g., growing nerve cells creep across the extracellular matrix with the help of nerve-cell adhesion molecules (NCAMs) -cell adhesion helps white blood cells escape from the circulation and move into infected tissues, and allows clumps of platelets to cling to damaged blood vessel -because cell adhesions are not permanent, the bond between those CAMs and matrix is weak

Answer 201

Three broad categories by function: -communicating junctions (in animals these are gap junctions) -occluding junctions (tight junctions) -anchoring junctions

Answer 202

-simplest cell-cell junctions -allow direct and rapid cell-to-cell communication through cytoplasmic bridges between adjoining cells -cylindrical proteins called connexins interlock to create passageways that look like hollow rivets with narrow channels through their centre -able to open and close, regulating the movement of small molecules and ions through them -gap junctions allow both chemical and electrical signals pass rapidly from one cell to the next.

Answer 203

-are occluding junctions that restrict the movement of material between the cells they link -the cells membranes of adjacent cells partly fuse together with the help of proteins called claudins and occludins, thereby making a barrier --> barrier properties of tight junctions are dynamic and can be altered depending on the body's needs -can vary in degrees of "leakiness" -tight junctions in the intestinal tract and kidney prevent most substances from moving freely between the external and internal environments --> enable cells to regulate what enters and leaves the body -tight junctions also create the blood-brain barrier that prevents many potentially harmful substances in the blood form reaching extracellular fluid of the brain

Answer 204

-attach cells to each other (cell-cell anchoring junctions) or to the extracellular matric (cell-matrix anchoring junctions). -in vertebrates, cell-cell anchoring junctions are created by CAMs called cadherins, which connect with one another across the intracellular space - cell-matric junctions use CAMs called integrins --> integrins are membrane proteins that can also bind to signal molecules in cells environment, transferring information carried by the signal across the cell membrane into the cytoplasm -contribute to the mechanical strength of the tissue (compared to zippers that ties cells together and hold them in positions, by interlocking cadherin proteins) --> is strong thereby allowing tissue in skin and lining body cavities to resist damage from stretching and twisting

Answer 205

-movement of materials between cells is known as the paracellular pathway --> tissues held together with anchoring junctions have spaces where they allow materials to pass from one side to the other

Answer 206

-Adherens junctions or desmosomes -adherens junctions link actin fibres in adjacent cells together -Desmosomes attach intermediate filaments of cytoskeleton --> strongest cell-cell junctions, in electron micrographs can be recognised by dense glycoprotein bodies, or plaques, that lie just inside membrane in the region where two cells connect -desmosomes may be small points of contact between two cells (spot desmosomes) or bands that encircle the entire cell (belt desmosomes

Answer 207

-Hemidesmosomes and Focal adhesions -hemidesmosomes are strong junctions that anchor intermediate fibres of cytoskeletons to fibrous matrix proteins such as laminin -Focal adhesions tie intracellular actin fibres to different matrix proteins, such as fibronectin

Answer 208

-disappearance of anchoring junctions probably contribute to the metastasis of cancer cells throughout the body -cancer cells lose their anchoring junctions because they have fewer cadherin molecules and are not bound as tightly to neighbouring cells -once a cancer cell is released from its mooring, it secretes protein-digesting enzymes known as proteases. These enzymes, especially those called matrix metalloproteinases (MMPs), dissolve the extracellular matrix so that escaping cancer cells can invade adjacent tissues or enter the bloodstream.

Answer 209

the internal environment of the body and regulate the exchange of materials between the internal and external environments. These tissues cover exposed surfaces, such as the skin, and line the internal passageways, such as the digestive tract

Answer 210

cross and epithelium

Answer 211

act as a barrier to keep water in the body and invaders such as bacteria out.

Answer 212

control the movement of materials between the external environment and the internal environment and extracellular fluid of the body

Answer 213

chemicals into the blood or into the external environment --> sweat and saliva are examples of substances that secreted by epithelia into environment. Hormones are secreted into the blood

Answer 214

one or more layers of cells connected to one another, with a thin layer of extracellular matrix lying between the epithelial cells and their underlying tissues. This matrix layer, called basal lamina, or basement membrane, is composed of a network of collagen and laminin filaments embedded in proteoglycans. The protein filaments hold the epithelial cells to the underlying cell layers, just as cell junctions hold the individual cells in the epithelium to one another.

Answer 215

Variable. Classify epithelia either as "leaky" or "tight", depending on how easily substances pass through one side of epithelial layer to the other.

Answer 216

anchoring junctions allow molecules to cross the epithelium by passing through the gap between two adjacent epithelial cells. A typical leaky epithelium is a wall of capillaries (smallest blood vessels), where all dissolved molecules except for large proteins can pass from the blood to the interstitial fluid by traveling through the gaps between adjacent epithelial cells.

Answer 217

Such as that in the kidney, adjacent cells are bound to each other by tight junctions that create a barrier, preventing substances from travelling between adjacent cells. To cross a tight epithelium, most substances must enter the epithelial cells and go through them. The tightness of an epithelium is directly related to how selective it is about what can move across it. Some epithelia, such as those of the intestine, have the ability to alter the tightness of their junctions according to the body's need.

Answer 218

Two general types: (1) sheets of tissue that lie on the surface of the body or that line the inside of the tubes and hollow organs (2) secretory epithelia that synthesize and release substances into the extracellular space

Answer 219

The number of cell layers in the tissue and by the shape of the cells in the surface layer. This classification scheme recognises two types of layer: simple (one cell thick) and stratified (multiple cell layer). Also recognises three cell shapes: squamous, cuboidal, and columnar.

Answer 220

Five functional types: -exchange -transporting -ciliated -protective -secretory

Answer 221

-composed of very thin, flattened cells that allow gases (CO2 and O2) to pass rapidly across the epithelium. -This type of epithelium lines blood vessels the lungs, the two major sites of gas exchange in the body. -In capillaries, gaps or pores in the epithelium also allows molecules smaller than proteins to pass between two adjacent epithelium cells, making this a leaky epithelium -histologists classify thin exchange tissue as simple squamous epithelium because it is a single later of thin, flattened cells -The simple squamous epithelium lining the heart and blood vessels is also called the endothelium

Answer 222

-actively and selectively regulate the exchange of nongaseous materials, such as ions and nutrients, between the internal and external environments. -These epithelia line the hollow tubes of the digestive system and the kidney, where lumens open into the external environment -Movement of material from the external environment across the epithelium to the internal environment is called absorption -movement in the opposite direction, from the internal to the eternal, is called secretion

Answer 223

By following characteristics: (1) Cell shape --> cells of transporting epithelia are much thicker than cells of exchange epithelia, and they act as a barrier as well as an entry point. The cell layer is only one cell thick (a simple epithelium), but cells are cuboidal or columnar. (2) Membrane modifications --> The apical membrane, the surface of the epithelial cell that faces the lumen, has tiny finger-like projections called microvilli that increase the surface area available for transport. A cell with microvilli has least 20 times the surface area of a cell without them. In addition, the basolateral membrane, the side of the epithelial cell facing the extracellular fluid, may also have folds that increase the cell's surface area (3) Cell junctions --> The cells of transporting epithelia are firmly attached to adjacent cells by moderately tight to very tight junctions. This means that to cross the epithelium, material must move into an epithelial cell on one side of the tissue and out of the cell on the other side (4) Cell organelles --> Most cells that transport materials have numerous mitochondria to provide energy for transport processes. The properties of transporting epithelia differ depending on where in the body the epithelia are located. E.g., glucose can cross epithelium of the small intestine and enter the extracellular fluid but cannot cross the epithelium of the large intestine

Answer 224

-are non-transporting tissues that line the respiratory system and parts of the reproductive tract. -The surface of the tissue facing the lumen is covered with cilia that beat in a coordinated, rhythmic fashion, moving fluid and particles across the surface of the tissue. -injury to cilia or to the epithelial cells can stop ciliary movement. E.g., smoking paralyzes the ciliated epithelium lining the respiratory tract. -loss of ciliary function contributes to the higher incidence of respiratory infection in smokers, when the mucus that traps bacteria can no longer be swept out of the lungs by the cilia

Answer 225

-Prevent exchange between the internal and external environments and protect areas subject to mechanical or chemical stresses. -These epithelia are stratified tissues, composed of many stacked layers of cells -protective epithelia may be toughened by the secretion of keratin, the same insoluble protein abundant in hair and nails -The epidermis (top layer of skin) and linings of the mouth, pharynx, oesophagus, urethra, and vagina are all protective epithelia - Because protective epithelia are subjected to irritating chemicals, bacteria, and other destructive forces, the cells in them have a short life span. In deeper layers, new cells are produced continuously, displacing older cells at the surface. As skin ages, the rate of cell turnover declines

Answer 226

-composed of cells that produce a substance and then secrete it into the extracellular space -Secretory cells may be scattered among other epithelial cells, or may group together to form a multicellular gland. -two types of secretory glands: exocrine and endocrine

Answer 227

-are secretory epithelia -release their secretions to the body's external environment --> leaves the body -This may be onto the surface of the skin or onto an epithelium lining one of the internal passageways, such as the airways of the lung or the lumen of the intestine. -most exocrine glands release their products through open tubes known as ducts. Sweat glands, mammary glands in the breast, salivary glands, the liver, and the pancreas are all exocrine glands -produce two types of secretions: serous secretions and mucous secretions -serous secretions are watery solutions, and many of them contain enzymes --> tears, sweat, and digestive enzymes solutions -mucous secretions (aka mucus) are sticky solutions containing glycoproteins and proteoglycans. -Some exocrine glands contain more than one type of secretory cell, produce both serous and mucous secretions --> e.g., salivary glands

Answer 228

-single exocrine cells that produce mucus. Mucus acts as a lubricant for food to be swallowed, as a trap for foreign particles and microorganisms inhaled or ingested, and as a protective barrier between the epithelium and the environment

Answer 229

-Unlike exocrine glands, endocrine glands are ductless and release their secretions, called hormones, into the body's extracellular compartment. -Hormones enter the blood for distribution to the other parts of the body, where they regulate or coordinate the activities of various tissues, organs, and organ systems. -e.g., pancreas, thyroid gland, gonads, and pituitary glands -isolated endocrine cells occur scattered in the epithelial lining of the digestive tract, in the tubules of the kidney, and in the walls of the heart.

Answer 230

-during development, the region of epithelium destined to become glandular tissue divides downward into the underlying connective tissue. -exocrine --> a hollow centre, or lumen, forms in exocrine glands, creating duct that provides a passageway for secretions to move to the surface of the epithelium, remain connected to the parent epithelium by a duct that transports the secretion to its destination (external environment). -Endocrine --> these lose the connecting bridge of cells that links them to the parent epithelium. Their secretions go directly into the bloodstream

Answer 231

-second major tissue type, provide structural support and sometimes a physical barrier that, along with specialised cells, helped defend the body from foreign invaders such as bacteria. -The distinguishing characteristics of connective tissues is the presence of extensive extracellular matrix containing widely scattered cells that secrete and modify the matrix -includes blood, support tissues for the skin and internal organs, and cartilage and bone

Answer 232

-extracellular matrix of connective tissue is a ground substance (aka matrix) of proteoglycans and water in which insoluble protein fibres are arranged. -consistency is highly variable, depending on the type of connective tissue --> from watery blood to bone -lie embedded in the extracellular matrix. These cells are described as fixed if they remain in one place and as mobile if they can move. -fixed cells are responsible for local maintenance, tissue repair and energy storage. -mobile cells are responsible mainly for defence. -distinction between fixed and mobile not absolute, because at least one cell type is found in both fixed and mobile forms -extracellular matrix is non-living, but connective tissue cells constantly modify it by adding, deleting, or rearranging molecules. -connective tissue cells produce matrix fibres --> four types of fibre proteins found in matrix, aggregated into insoluble fibres: Collagen, elastin, fibrillin and fibronectin.

Answer 233

- suffix -blast one connective tissue indicated cell growing or actively secreting extracellular matrix. E.g., fibroblasts are connective tissues that secrete collagen-rich matrix - suffix -clast are actively breaking down matrix - suffix -cyte are neither growing, secreting matrix components, nor breaking down matrix

Answer 234

-most abundant protein in human body, almost one-third of body's dry weight -most diverse of the four protein types, as least 12 variations -found almost everywhere connective is found, from skin to muscles and bones -individual collagen molecules pack together to form collagen fibres, flexible but inelastic fibres whose strengths per unit weight exceeds that of steel -amount and arrangement of collagen fibres help determine mechanical properties of different types of connective tissues

Answer 235

-coiled, wavy protein that returns to its original length after being stretched. This property known as elastance or elastic recoil. -elastin combines with the very thin, straight fibres of fibrillin to form filaments and sheets of elastic fibres. These two fibres important in elastic tissues such as lungs, blood vessels and skin -fibronectin connects cells to extracellular matric at focal adhesions. Fibronectins also play an important role in wound healing and in blood clotting

Answer 236

-loose and dense connective tissue, adipose tissue, blood, cartilage, and bone

Answer 237

-loose connective tissues are elastic tissues that underlie skin and provide support for small glands -dense connective tissue (irregular and regular) provide strength or flexibility --> e.g., tendons, ligaments, and the sheaths that surround muscles and nerves (in these dense tissues collagen fibres are the dominant type)

Answer 238

-are dense connective tissue -tendons attach skeletal muscles to bones -ligaments connect one bone to another -because ligaments contain elastic fibre in addition to collagen fibres, they have a limited ability to stretch -tendons lack elastic fibres and so cannot stretch

Answer 239

-Cartilage and bone together are consider supporting connective tissues -These tissues have a dense ground substance that contains closely packed fibres -cartilage is found in structures such as nose, ears, knee, and windpipe. Is solid, flexible and notable for its lack of blood supply --> so nutrients and oxygen must reach cells of cartilage by diffusion (slow process, is why damaged cartilage heals slowly) - chondrocytes are cells that synthesize extracellular matrix of cartilage -Fibrous extracellular matrix of bone is said to be calcified because it contains mineral deposits, primarily calcium salts, such as calcium phosphates --> these minerals give the bone strength and rigidity.

Answer 240

adipocytes, or fat cells

Answer 241

-an adipocyte of white fat typically contains a single enormous lipid droplet that occupies most of the volume of the cell. Most common form of adipose tissue in adults -brown fat is composed of adipose cells that contain multiple lipid droplets rather than a single large droplet. This type of fat plays role in temperature regulation in infants --> not completely absent in adults

Answer 242

-characterised by watery extracellular matrix called plasma -plasma consists of a dilute solution of ions and dissolved organic molecules, including a large variety of soluble proteins -blood cells and cell fragments are suspended in the plasma, but insoluble protein fibres typical of other connective tissue are absent -consists of liquid matrix (plasma) plus red and white blood cells and cell fragments called platelets

Answer 243

-muscle and neural tissues connectively called excitable tissues because of their ability to generate and propagate electrical signals called action potentials. -both have minimal extracellular matrix, usually limited to a supportive layer called the external lamina -some types of muscles and nerve cells are also notable for their gap junctions, which all the direct and rapid conduction of electrical signals form cell to cell -muscle tissue has ability to contract and produce force and movement. Body contains three types of muscle tissues: cardiac muscle in heart; smooth muscle, which makes up most of internal organs; and skeletal muscle, most skeletal muscles attach to bones and are responsible for gross movement of body -neural tissue has two types of cells: neurons, or nerve cells, carry information in the form of chemical and electrical signals from one part of body to other; Glial cells, or neuroglia, are support cells for neurons

Answer 244

necrosis and apoptosis

Answer 245

-cells die from physical trauma, toxins, or lack of oxygen when their blood supply is cut off -necrotic cells swell, their organelles deteriorate, and finally cells rupture. -Cell contents released this way include digestive enzymes that damage adjacent cells and trigger an inflammatory response. -You see necrosis when you have red are of skin surrounding a scab

Answer 246

-aka programmed cell death OR cell suicide -do not disrupt their neighbours when they die -Some signals keep apoptosis from occurring, others tell cell to self-destruct -when suicide signal wins, chromatin in nucleus condenses, cell pulls away from its neighbour, it shrinks, then breaks up into tide membrane-bound blebs that are gobbled up by neighbouring cells or wandering cells of immune system -apoptosis normal event. During foetal development, apoptosis removes unneeded cells, such as half cells in the developing brain and webs of skin between finger and toes. In adults cells that are subject to wear and tears form exposure to outside environment may live only a day or two before undergoing apoptosis. E.g., intestinal epithelium completely replaces with new cells every two - five days

Answer 247

- Layer 1 - epidermis consists of multiple cells layers that create a protective barrier - Layer 2 - dermis is loose connective tissue that contains exocrine glands, blood vessels, muscles, and nerve endings -Layer 3 - hypodermis contains adipose tissue for insulation -sweat glands secrete a dilute salt fluid to cool body -apocrine glands in genitalia, anus, axillae (armpit), and eyelids release waxy or viscous milky secretions in response to fear or sexual excitement -sebaceous glands are exocrine glands that secrete a lipid mixture -arrector pili muscles pull hair follicles into a vertical position when the muscle contracts, creating "goose bumps" -hair follicles secrete the non-living keratin shaft of hair

Answer 248

-phospholipid matrix acts as the skins main waterproofing agent. Surface keratinocytes produce keratin fibres - epidermal cells - Desmosomes anchor epithelial cells to each other -melanocytes contain the pigment melanin

Answer 249

-hemidesmosomes tie epidermal cells to fibres of basal lamina -basal lamina or basement membrane is an acellular layer between epidermis and dermis

Answer 250

-earliest cells in life of human being said to be totipotent because they have the ability to develop into any and all types of specialised cells. Any totipotent cell has potential to become a functioning organism

Answer 251

begin to specialise, or differentiate between. As they do so, they narrow their potential fate and become pluripotent.

Answer 252

-can develop into many different cell types but not all cell types - isolated pluripotent cell cannot develop into an organism

Answer 253

develop into the various tissues of the body. As the cells specialise and mature, many lose the ability to undergo mitosis and reproduce themselves. They can be replaced, however by new cells created from stem cells

Answer 254

-less specialised (relative to pluripotent and totipotent cells) that retain the ability to divide. -undifferentiated stem cells in a tissue that retain the ability to divide and develop into the cell types of that tissue are said to be multipotent. -some of most studied multipotent adult stem cells are found in bone marrow and give rise to blood cells -all adult stem cells occur in small number

Answer 255

groups of tissues that carry out related functions

Answer 256

respiration, which consumes oxygen and produces carbon dioxide and water.

Answer 257

the capacity to do work

Answer 258

one of three specific things; -chemical work -transport work -mechanical work

Answer 259

-is making and breaking of chemical bonds. -enables cells and organisms to grow, maintain a suitable internal environment, and store information needed for reproduction and other activities -e.g., forming the chemical bond of a protein

Answer 260

-enables cells to move ions, molecules, and larger particles through the cell membrane and through the membranes organelles in the cell -Transport work is particularly useful for creating concentration gradients.

Answer 261

-in animals is used for movement -at cellular level, movement includes organelles moving around in a cell, cells changing shape, and cilia and flagella beating -at macroscopic level in animals, movement usually involves muscles contraction. -Most mechanical work is mediated by motor proteins that make up certain intracellular fibres and filaments of the cytoskeleton

Answer 262

Kinetic and potential

Answer 263

-Kinetic: energy of motion -Potential: is stored energy

Answer 264

No, certain amount of energy is lost to the environment, usually heat

Answer 265

efficiency of the process

Answer 266

-aka law of conservation of energy -states that the total amount of energy in the universe is constants -universal considered to be closed system (nothing enters of leaves) -energy can be converted, but total amount of energy in closed system never changes

Answer 267

-no, it is an open system, it exchanges materials and energy with its surroundings

Answer 268

-states that natural spontaneous processes move from a state of order (non-randomness) to a condition of randomness or disorder, aka entropy. -in open system disorder occurs when energy lose to the environment occurs without regaining it --> we say that the entropy of open system has increased

Answer 269

-the study of energy flow through biological systems

Answer 270

-in chemical reactions substance becomes a different substance, usually by breaking and/or making of covalent bonds -begins with one or more molecules called reactants and ends with one or more molecules called products - speed with which a reaction takes place, the reaction rate, is the disappearance rate of the reactants (A and B) or the appearance rate of the products (C and D) --> measured as change in concentration during certain rime period, often molarity per second (M/sec)

Answer 271

potential energy stored in the chemical bonds of a molecule

Answer 272

The energy required to initiate a reaction is known as the activation energy for the reaction.

Answer 273

The difference in free energy between reactants and products is the net free energy change of the reaction.

Answer 274

-is the initial input of energy required to bring reactants into a position that allows them to react with one another --> this "push" needed to start reaction -a reaction with low activation energy proceeds spontaneously when the reactants are brought together -reactions with high activation energies either do not proceed spontaneously or proceed to slowly to be useful

Answer 275

means that the reaction has either released or trapped energy

Answer 276

-if the free energy of the products is lower than the free energy of the reactants the reaction releases energy and is called an exergonic reaction -energy released by an exergonic reaction may be used by other molecules to do work or may be given off as heat

Answer 277

-products retain part of activation energy that was added, making their free energy greater than that of reactants -these require a net input of energy -some of the energy added to endergonic reaction remains trapped in the chemical bonds of the produces. -These energy-consuming reactions are often synthesis reactions, in which complex molecules are made from smaller molecules --> e.g., endergonic reaction links may glucose molecules together to create the glucose polymer glycogen. The complex glycogen molecule has more free energy than the simple glucose molecules used to make it

Answer 278

it releases energy as it proceeds in the reverse direction

Answer 279

-simplest way for cell to acquire activation energy is to couple an exergonic reaction to an endergonic reaction. Some of the most familiar couple reactions are those that use the energy released by breaking the high-energy bond of ATP to drive an endergonic reaction, in this type of coupled reaction, the two reactions take place simultaneously and in same location.

Answer 280

-a chemical reaction that can proceed in both directions ---> net free energy change of reaction plays important role in determining whether that reaction can be reversed. Because the net free energy change of the forward reaction contributes to the activation energy of the reverse reaction

Answer 281

-proteins that speed up the rate of chemical reactions -during these reactions, the enzyme molecules are not changed in any way, meaning they are biological catalysts -in enzymatically catalysed reactions, the reactant A and B are substrates (A + B --enzyme--> C + D)

Answer 282

specificity, competition, and saturation

Answer 283

-enzymes that comes in a variety of related forms (isoforms) and are known as isozymes of one another -enzymes that catalyse the same reaction but under different conditions or in different tissues -structures of related isozymes are slightly different, which causes the variability in their activity

Answer 284

-measure rate of enzymatic reaction by monitoring either how fast the products are synthesized or how fast the substrates are consumed. -reaction rate can be altered by changes in temperature, amount of enzyme present, and substrate concentrations -in mammals, temperature considered to be essentially constant, therefore enzyme amount and substrate concentration are two main variables that affect reaction rate

Answer 285

-in protein-binding interactions, if the amount of protein (enzyme) is constant, the reaction rate is proportional to substrate concentration. -cells control reaction rates by regulating amount of enzyme in cell --> absence of enzyme, reaction goes slowly or not at all. -if enzymes present, the rate of reaction proportional to amount of enzyme and amount of substrate - if there is so much substrate that all enzyme binding sites are saturated and working at maximum capacity, the reaction rate with reach a maximum. -what determines direction reactions goes in this situation? --> reversible reactions go to state of equilibrium

Answer 286

-proenzymes or zymogens -some are synthesised as inactive molecules and activated on demand by proteolytic activation -others require the binding of inorganic cofactors, such as Ca2+ or Mg2+ before they become active

Answer 287

-organic cofactors for enzymes -do not alter the enzymes binding site as inorganic cofactors do -act as receptors and carriers for atoms or functional groups that are removed from the substrate during the reaction. Although coenzymes needed for some metabolic reactions to take place, they are not required in large amounts -many substances we call vitamins are the precursors of coenzymes

Answer 288

-may be inactivated by inhibitors or becoming denatured -modulated by chemical factors or changes in temperature and pH.

Answer 289

-how does an enzyme increase the rate of reaction? --> it lowers activation energy, making it more likely that reaction will start -accomplish this by binding their substance and bringing them into the best position for reacting with each other.

Answer 290

Most can be classified into four categories: -oxidation-reduction -hydrolysis-dehydration -exchange-addition-substation -ligation

Answer 291

-most important reactions in energy extraction and transfer in cells -these reactions transfer electrons from one molecule to another -a molecules that gained an electron is said to be reduced -molecules that lose electrons said to be oxidized -mnemonic OIL RIG (Oxidation Is Loss (of electrons), Reduction Is Gain)

Answer 292

-important in the breakdown and synthesis of large biomolecules -in dehydration reactions, a water molecule is one of the products --> in many dehydration reactions, two molecules combine into one, losing water in the process --> when dehydration reaction results in synthesis of new molecule, process known as dehydration synthesis -in hydrolysis reactions, a substrate changed into one or more products through addition of water. --> in these reactions, covalent bonds of water molecules are broken ("lysed") so that the water reacts as a hydroxyl group OH- and a hydrogen ion H+ -when enzyme name consists of substrate name plus the suffix -ase, the enzyme causes a hydrolysis reaction. E.g., lipase, breaks up large lipids into smaller ones using hydrolysis

Answer 293

-addition reaction adds functional group to one or more substrates -subtraction reaction removes functional group from one or more of the substances -functional groups are exchanged between or among substrates during exchange reactions

Answer 294

-deamination - removal of an amino acid group -amination - additional of an amino group -transamination - transfer of an amino group from one molecule to another

Answer 295

-Join two molecules together using enzymes known as synthetases and energy from ATP. -e.g., synthesis of acetyl coenzyme A (acetyl CoA) from fatty acids and coenzyme A.

Answer 296

-all chemical reactions that take place in an organism -these reactions (1) extract energy from nutrient biomolecules (such as proteins, carbohydrate, and lipids) and (2) either synthesize or break down molecules.

Answer 297

-catabolism - reactions that release energy through the breakdown of large biomolecules -anabolism - energy-utilizing reactions that result in the synthesis of large biomolecules.

Answer 298

-energy release from or stored in the chemical bonds of biomolecules during metabolism is commonly measured in kilocalories (kcal) -kilocalorie is the amount of energy needed to raise the temperature of 1 litre of water by 1 degree Celsius. -kilocalorie is the same as a Calorie (capital C), used for quantifying energy of food -One kilocalorie is also equal to 1,000 calories (small c)

Answer 299

in the high-energy phosphate bonds of ATP or in the high-energy electrons of NADH, FADH2, or NADPH. Anabolic reactions then transfer energy from these temporary carriers to the covalent bonds in bionolecules

Answer 300

highly coordinated chemical reactions in which the activities taking place in a cell at any given moment are matched to the needs of the cell. Each step in a metabolic pathway proceed in sequence. Substrate A is changed into product B, which then becomes the substrate for the next reaction in the pathway, which then becomes the substrate for the next reaction in the pathway. A --> B --> C --> D -molecules of the pathway are called intermediates, because products of one reaction become substrates of the next

Answer 301

In five basic ways: (1) By controlling enzyme concentrations (2) By producing modulators that change reaction rates (3) By using two different enzymes to catalyse reversible reactions (4) By compartmentalising enzymes within intracellular organelles (5) By maintaining an optimum ratio of ATP to ADP

Answer 302

-For enzymes, the production of modulators is frequently controlled by hormones and other signals coming from outside the cell - This type of outside regulation is a key element in the integrate control of the body's metabolism following a meal of during periods of fasting between meals - some metabolic pathways have their own built-in form of modulation, called feedback inhibition. In this form of modulation, the end product of a pathway (Z) acts as an inhibitory modulator of the pathway. A -- (enzyme 1) --> B -- (enzyme 2) --> C -- (enzyme 3) --> Z --(feedback inhibition) --> enzyme 1 - As the pathway proceeds and Z accumulates, end product Z feeds back and inhibits the enzyme catalysing the conversion of A to B. -Inhibition of the enzyme slows down production of Z until the cell can use it up. -Once the levels of Z fall, feedback inhibition on enzyme 1 is removed and the pathway starts to run again. Because Z is the end product of the pathway, this type of feedback inhibition is sometimes called end-product inhibition

Answer 303

-cells can use reversible reactions to regulate the rate and direction of metabolism -if a single enzyme can catalyse the reaction in either direction, the reaction will go to a state of equilibrium, as determined by the law of mass action -such as reaction, therefore, cannot be closely regulated except by modulators and by controlling the amount of enzyme -however, if a reversible reaction requires two different enzymes, one for the forward reaction and one for the reverse reaction, the cell can regulate the reaction more closely -if no enzyme for the reverse reaction is present in the cell, the reaction is irreversible

Answer 304

-Many enzymes of metabolism are isolated in specific subcellular compartments -some, like the enzymes of carbohydrate metabolism, are dissolved in the cytosol, whereas others are isolated within specific organelles -Mitochondria, ER, Golgi apparatus, and lysosomes all contain enzymes that are not found in the cytosol -This separation of enzymes means that the pathways controlled by the enzymes are also separated. That allows the cell to control metabolism by regulating the movement of substrate from one cellular compartment to another

Answer 305

-the ratio of ATP and ADP in the cell determines whether pathways that result in ATP synthesis are turned on or off. -When ATP levels are high, production of ATP decreases -When ATP levels are low, the cell sends substrates through pathways that result in more ATP synthesis

Answer 306

-usefulness of metabolic pathways as suppliers of energy is often measured in terms of the net amount of ATP the pathways yield -ATP is nucleotide containing three phosphate groups. One of the three phosphate groups is attached to ADP by a covalent bond in an energy-requiring reaction -energy is stored in this high-energy phosphate bond and then released when the bond is broken during the removal of the phosphate group. Show by: ADP + Pi + energy <---> ADP (squiggle) P (=ATP) -squiggle indicates a high energy bond, Pi is abbreviation for an inorganic phosphate group. -estimates of the amount of free energy released when a high-energy phosphate bond is broken range from 7 to 12 kcal per mole of ATP. - in few cases, the energy used to make high-energy bonds of a related nucleotide guanosine triphosphate, GTP. The body stores its energy in the chemical bonds of lipids or the glucose polymer glycogen

Answer 307

-metabolic pathways that yield the most ATP molecules are those the require oxygen - aerobic, or oxidative pathways. -anaerobic pathways, which are those that can proceed without oxygen, also produce ATP molecules but in much smaller quantities

Answer 308

-in glycolysis, metabolism of one glucose molecule (C6H12O6) has a net yield of two 3-carbon pyruvate molecules, 2 ATP, and high-energy electrons carried on 2 NADH -in next phase, the conversion of pyruvate to acetyl CoA produces one NADH. Carbons from one acetyl CoA going through one acetyl CoA going through the citric acid cycle trap energy in 3 NADH molecules, 1 FADH2 and 1 ATP --> these steps happen twice for each glucose, giving a total yield of 8 NADH, 2 FADH2, and 2 ATP for the pyruvate-citric acid cycle phase of glucose metabolism -in final step, high-energy electrons of NADH and FADH2 passing along the proteins of the electron transport system use their energy to concentrate H+ in the intermembrane compartment of the mitochondria -When the H+ move down their concentration gradient through a channel in the ATP synthase, the energy released is transferred to the high-energy phosphate bond of ATP. -One average, the NADH and FADH2 from one glucose produce 26-28 ATP --> maximum potential energy yield for catabolism of one glucose molecule through aerobic pathways comes to 30-32 ATP --> potential maxes, mitochondria often don't work up to this capacity

Answer 309

-a certain number H+ ions leak from the intermembrane space back into the mitochondrial matrix without producing an ATP -number of ATP produced per glucose comes from the two cytosolic NADH molecules produced during glycolysis. These NADH molecules are unable to enter mitochondria and must transfer their electrons through membrane carriers. Inside a mitochondrion, some of these electrons go to FADH2, which has a potential average yield of only 1.5 ATP rather than the 2.5 ATP made by mitochondria NADH. If cytosolic electrons go to mitochondrial NADH instead, they produce two additional ATP molecules

Answer 310

-when a cell whose oxygen supply cannot keep pace with its ATP demand, metabolism of glucose shifts from aerobic to anaerobic metabolism, starting at pyruvate. - in anaerobic glucose metabolism, pyruvate is converted to lactate instead of being transported into the mitochondria -pyruvate is a branch point for metabolic pathways. Depending on a cell's needs and oxygen content, pyruvate can be shuttled into the citric acid cycle or diverted into lactate production until oxygen supply improves -Conversion of pyruvate to lactate changed one NADH back to NAD+ when a hydrogen atom and an electron are transferred to the lactate molecule -as a result, the net energy yield for the anaerobic metabolism of one glucose molecule is 2 ATP and 0 NADH. -anaerobic metabolism is low efficiency, i.e., 2 ATP compared to 30-32 ATP

Answer 311

-located in the inner mitochondrial membrane -The synthesis of ATP using ETA is called oxidative phosphorylation because the system requires oxygen to act as the final acceptor of electrons and H+ Steps: (1) NADH and FADH2 release high-energy electrons and H + to the ETS. NAD+ and FAD are coenzymes that recycle. (2) Energy released when pairs of high-energy electrons pass along the transport system is used to concentrate H+ from the mitochondrial matrix in the intermembrane space. The H+ concentration gradient is a source of potential energy. (3) By the end of the ETS, the electrons have given up their stored energy (4) Each pair of electrons released by the ETS combines with two H+ and an oxygen atom, creating a molecule of water, H2O (5) As H+ move down their concentration gradient through a protein known as ATP synthase, the synthase transfers their kinetic energy to the high-energy phosphate bond of ATP. * Each 3 H+ that shuttle through the ATP synthase make a maximum of 1 ATP. * A portion of the kinetic energy is released as heat.

Answer 312

-Only four nitrogenous bases in the DNA molecule—adenine (A), guanine (G), cytosine (C), and thymine (T) --- RNA substitutes the base uracil (U) for the DNA base thymine - If triplets of bases were the codes for different molecules, however, DNA could create 4^3 or 64 different amino acids. These triplets, called codons, are the way information is encoded in DNA and RNA -one DNA codon (TAC) acts as the initiator or start codon that signifies the beginning of a coding sequence -Three codons serve as terminator or stop codons that show where the sequence ends. -The remaining 60 triplets all code for amino acids.

Answer 313

-A gene is defined as a region of DNA containing the information necessary to produce a functional piece of RNA, which subsequently aids in protein synthesis. -A gene contains the information required to produce a functional piece of RNA.

Answer 314

(1) A section of DNA containing a gene must be activated so that its code ca be read (2) DNA base sequence of gene is used to create a piece of RNA in the process known as transcription (3) Messenger RNA is processed in the nucleus after it is made --> may undergo alternative splicing before leaving nucleus or be "silence" and destroyed by enzymes through RNA interference. (4) Processed mRNA leaves the nucleus and enter the cytosol. There it works with tRNA and rRNA to direct translation, the assembly of amino acids into a protein chain (5) Newly synthesized proteins are then subject to posttranslational modification --> They fold into complex shapes, may be split enzymes into smaller peptides, or have various chemical groups added to them

Answer 315

Constitutively active genes are continuously transcribed into RNA messages and usually encode proteins essential for ongoing cell functions. In contrast, regulated genes can have their activity modulated by regulatory proteins, being turned on (induced) or off (repressed).

Answer 316

-messenger RNA (mRNA) -transfer RNA (tRNA) -ribosomal RNA (rRNA)

Answer 317

-Transcription uses DNA as a template to create a small single strand of RNA that can leaves nucleus -Synthesis of RNA from the double stranded DNA template requires an enzyme known as RNA polymerase, plus magnesium or manganese ions and energy in the form of high-energy phosphate bonds -a promoter region that precedes the gene must be activated before transcription can begin -regulatory-protein transcription factors bind to DNA and activate the promoter -promoter region not transcribed into RNA -each base in the DNA template strand pairs with its complementary RNA base (G-C, C-G, T-A, A-U), similar to DNA synthesis. Steps: (1) The active promoter tells the RNA polymerase where to bind to the DNA (2) Polymerase moves along the DNA molecule and "unwinds" the double strand by breaking the hydrogen bonds between paired bases (3) One strand of DNA, called the template strand, serves as the guide for the RNA synthesis, RNA bases bind to DNA creating a single strand of mRNA (4) When RNA polymerase reaches stop codon stops adding bases, and mRNA and the RNA polymerase detach from DNA, and the mRNA goes to the cytosol after processing

Answer 318

Bases are linked during transcription at an average rate of 40 per second

Answer 319

Transcription of large RNAs in humans may take more than a minute, as they can contain as many as 5,000 bases

Answer 320

The next step is mRNA processing, which occurs in two forms: RNA interference and alternative splicing

Answer 321

In RNA interference, newly synthesized mRNA is inactivated or destroyed before it can be translated into proteins.

Answer 322

Enzymes clip segments out of the middle or off the ends of the mRNA strand, and other enzymes splice the remaining pieces back together. This process is necessary because genes contain both coding segments (exons) and noncoding segments (introns) in their DNA sequences

Answer 323

Alternative splicing is necessary because the mRNA initially transcribed from a gene's DNA contains noncoding segments (introns) that must be removed before the mRNA can leave the nucleus, resulting in a smaller piece of mRNA containing only the coding sequence for a specific protein

Answer 324

Alternative splicing allows a single DNA sequence to code for more than one protein by varying which segments are included in the final mRNA.

Answer 325

After processing, mRNA exits the nucleus through nuclear pores and travels to ribosomes in the cytosol, where it directs the construction of proteins

Answer 326

Coding segments are referred to as exons, while noncoding segments are called introns.

Answer 327

introns are removed from the mRNA strand during processing, leaving only the exons that encode the protein sequence

Answer 328

Processed mRNA binds to ribosomes, which are composed of protein and several types of rRNA

Answer 329

Ribosomes have two subunits, one large and one small, which come together when protein synthesis begins. The small ribosomal subunit binds to mRNA, followed by the addition of the large subunit, sandwiching the mRNA in the middle

Answer 330

tRNA assists in matching mRNA codons to the proper amino acid. Each tRNA contains an anticodon, a three-base sequence complementary to an mRNA codon, and carries a specific amino acid.

Answer 331

Amino acids are linked by dehydration synthesis, forming a peptide bond between the amino group (-NH2) of the newly arrived amino acid and the carboxyl end (-COOH) of the peptide chain

Answer 332

Once a peptide bond is formed, mRNA releases the "empty" tRNA, which can then attach to another amino acid molecule with the aid of a cytosolic enzyme and ATP

Answer 333

During the termination stage, the last amino acid is joined to the newly synthesized peptide chain, and the mRNA, the peptide, and the ribosomal subunits separate. The ribosomes are then ready for a new round of protein synthesis.

Answer 334

After protein synthesis is complete, mRNA is broken down by enzymes known as ribonucleases. Some forms of mRNA are broken down rapidly, while others may linger in the cytosol and be translated multiple times

Answer 335

This process is called protein sorting

Answer 336

A sorting signal is an address label carried by many newly made proteins, which directs the protein to its intended location within the cell

Answer 337

Proteins synthesized on cytosolic ribosomes without sorting signals remain in the cytosol after being released from the ribosome.

Answer 338

A signal sequence is a special segment of amino acids that serves as a sorting signal, directing the protein to the proper organelle and facilitating its transport through the organelle membrane.

Answer 339

Peptides synthesized on ribosomes attached to the rough ER have a signal sequence that directs them through the membrane of the rough ER and into the lumen of the organelle

Answer 340

Once a protein enters the ER lumen, enzymes remove the signal sequence

Answer 341

The initial step is the formation of the peptide's secondary structure, which may be an alpha helix or a beta strand.

Answer 342

A peptide achieves its final shape through the formation of hydrogen bonds, covalent bonds, and ionic bonds between amino acids in the chain.

Answer 343

Molecular chaperones are helper proteins that facilitate protein folding, ensuring proper three-dimensional structure

Answer 344

Misfolded proteins and proteins targeted for destruction are tagged with ubiquitin and sent to proteasomes, cylindrical cytoplasmic enzyme complexes responsible for breaking down proteins.

Answer 345

Disulfide bonds (S-S) are covalent bonds between two cysteine amino acids, which contain sulfur atoms

Answer 346

-Some biologically active proteins, including enzymes and hormones, are synthesized initially as inactive molecules - Before becoming active, these inactive molecules must have segments removed. -Posttranslational processing also activates some peptide hormones.

Answer 347

Chymotrypsin must have two small peptide fragments removed before it can catalyze a reaction

Answer 348

Proteins can be modified by the addition of sugars (glycosylation) to create glycoproteins or by combining with lipids to make lipoproteins

Answer 349

phosphate groups (PO4^(2-)) and methyl groups (-CH3).

Answer 350

Water is able to move freely in and out of nearly every cell in the body by traversing water-filled ion channels and special water channels created by the protein aquaporin (AQP)

Answer 351

In osmosis, water moves to dilute the more concentrated solution.

Answer 352

-Osmosis can be quantitatively measured by determining the osmotic pressure of a solution. -In the setup, the solution to be measured is placed in compartment B with pure water in compartment A. Because compartment B has a higher solute concentration than compartment A, water will naturally flow from A to B. However, by pushing down on the piston, water can be prevented from entering compartment B. -The pressure on the piston that exactly opposes the osmotic movement of water into compartment B is known as the osmotic pressure of solution B.

Answer 353

-The units for osmotic pressure are atmospheres (atm) or millimeters of mercury (mm Hg). -A pressure of 1 mm Hg is equivalent to the pressure exerted on a 1 cm^2 area by a 1-mm-high column of mercury

Answer 354

Molarity is defined as the number of moles of dissolved solute per liter of solution.

Answer 355

-Osmolarity is the concentration of osmotically active particles (ions or intact molecules) per litre of solution. It differs from molarity because it accounts for the number of particles in solution, not just the number of molecules -Osmolarity is expressed in osmoles per liter (osmol/L or OsM) or, for very dilute physiological solutions, milliosmoles per liter (mOsM).

Answer 356

molarity (mol/L) x particles/molecule (osmol/mol) = osmolarity (osmol/L)

Answer 357

Osmolarity describes only the number of particles in a solution and does not indicate the composition of the particles

Answer 358

Osmolality is concentration expressed as osmoles of solute per kilogram of water. It is related to osmolarity, which is expressed per liter of solution

Answer 359

If two solutions contain the same number of solute particles per unit volume, they are described as isosmotic

Answer 360

If one solution has a higher osmolarity (contains more particles per unit volume) than another, it is described as hyperosmotic to the other. Conversely, the solution with fewer osmoles per unit volume is described as hyposmotic to the other.

Answer 361

Osmolarity is a colligative property of solutions, meaning it depends strictly on the number of particles per liter of solution. It does not provide information about the nature of the particles or their behavior

Answer 362

Tonicity is a physiological term used to describe a solution and how it would affect cell volume if the cell were placed in the solution and allowed to come to equilibrium. If a cell placed in the solution gains water at equilibrium and swells, the solution is described as hypotonic to the cell. If the cell loses water and shrinks at equilibrium, the solution is hypertonic. If the cell does not change size at equilibrium, the solution is isotonic.

Answer 363

1. Osmolarity describes the number of solute particles dissolved in a volume of solution and has units, such as osmoles/liter. Tonicity, however, has no units and is only a comparative term. 2. Osmolarity can be used to compare any two solutions, and the relationship is reciprocal (solution A is hyperosmotic to solution B; therefore, solution B is hyposmotic to solution A). Tonicity always compares a solution and a cell, and by convention, tonicity is used to describe only the solution—for example, “Solution A is hypotonic to red blood cells.” 3. Osmolarity alone does not indicate what happens to a cell placed in a solution, while tonicity, by definition, tells you what happens to cell volume at equilibrium when the cell is placed in the solution

Answer 364

-Tonicity depends on the concentration of nonpenetrating solutes only. Nonpenetrating solutes are solute particles (ions or molecules) that cannot cross the cell membrane. -Nonpenetrating solutes (NaCl being most important) are crucial in predicting tonicity. Water will move until the concentrations of nonpenetrating solutes in the cell and the solution are equal.

Answer 365

1. If the cell has a higher concentration of nonpenetrating solutes than the solution, water moves into the cell, causing it to swell, and the solution is hypotonic. 2. If the cell has a lower concentration of nonpenetrating solutes than the solution, water moves out of the cell, causing it to shrink, and the solution is hypertonic. 3. If the concentrations of nonpenetrating solutes are the same in the cell and the solution, there is no net movement of water at equilibrium, and the solution is isotonic to the cell.

Answer 366

Tonicity and osmolarity are related, but there are exceptions. While a hyposmotic solution is always hypotonic because the cell will always have a higher concentration of nonpenetrating solutes than the solution, an isosmotic solution may be isotonic or hypotonic. It can never be hypertonic because it can never have a higher concentration of nonpenetrating solutes than the cell. Hyperosmotic solutions may be hypertonic, isotonic, or hypotonic, depending on the relative concentration of nonpenetrating solutes compared to the cell

Answer 367

-Hyposmotic solutions are always hypotonic because the cell will always have a higher concentration of nonpenetrating solutes than the solution. -Isosmotic solutions may be isotonic or hypotonic, depending on whether there are penetrating solutes present. If all solutes are nonpenetrating, the solution is isotonic; if there are penetrating solutes, it is hypotonic. -Hyperosmotic solutions' tonicity depends on the relative concentration of nonpenetrating solutes compared to the cell, and they can be hypertonic, isotonic, or hypotonic.

Answer 368

Defining volumes and concentrations allows mathematical determination of changes to volumes and osmolarity using the equation: solute/volume = concentration. This approach helps in understanding alterations in volume and osmolarity, such as in scenarios of dehydration.

Answer 369

Bulk flow is the most general form of biological transport, where fluid flows from regions of higher pressure to regions of lower pressure, carrying all its component parts, including dissolved or suspended substances. For example, blood moving through the circulatory system and air flow in the lungs are examples of bulk flow

Answer 370

Small molecules and lipid-soluble molecules, such as oxygen, carbon dioxide, and lipids, can easily cross most cell membranes. However, ions, polar molecules, and large molecules like proteins have more difficulty or may not enter at all. The size and lipid solubility of a molecule influence its movement across membrane

Answer 371

One scheme categorizes movement based on physical requirements: diffusion directly through the phospholipid bilayer, crossing with the aid of membrane proteins, or entering the cell in a vesicle. Another scheme classifies movement based on energy requirements: passive transport, which relies on concentration gradients, and active transport, which requires external energy input, such as ATP.

Answer 372

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. It has several properties: -Passive process: Diffusion does not require external energy input; it relies on the kinetic energy of molecules. -Movement down a concentration gradient: Molecules move from regions of higher concentration to regions of lower concentration. -Equilibrium: Diffusion continues until the concentration is equal everywhere, reaching dynamic equilibrium. -Rate dependent on concentration gradient and distance: Diffusion is faster with larger concentration gradients and over shorter distances. -Temperature dependence: Diffusion rates increase with higher temperatures due to faster molecular motion. -Inverse relationship with molecular size: Smaller molecules diffuse faster than larger ones. -Can occur in open systems or across partitions: Diffusion can happen in an open environment or across barriers that permit molecule movement.

Answer 373

Simple diffusion is the passive movement of molecules directly across the phospholipid bilayer of a membrane. Unlike diffusion in an open system, where molecules spread freely throughout the entire system, simple diffusion is restricted to molecules that are lipid-soluble (lipophilic) and can dissolve in the lipid core of the membrane

Answer 374

These are properties of simple diffusion, the ones about diffusion are applied, but these are additionally applied: -The rate of diffusion across a membrane in simple diffusion depends on the ability of the diffusing molecule to dissolve in the lipid layer of the membrane, also known as membrane permeability. Lipophilic molecules, including lipids, steroids, and small lipophilic molecules, can move across membranes by simple diffusion. However, the rate of water diffusion across membranes depends on the composition of the phospholipid bilayer, with membranes high in cholesterol being less permeable to water. Additionally, the rate of diffusion is directly proportional to the surface area of the membrane -The larger the surface area of the membrane, the more molecules can diffuse across per unit time. In physiology, changes in surface area can significantly impact diffusion rates. For example, in emphysema, where lung tissue breaks down and reduces the surface area available for oxygen diffusion, less oxygen can enter the body, leading to impaired oxygen delivery to cells and restricted physical activity

Answer 375

- Fick's Law of Diffusion describes the rate at which molecules move across a membrane, stating that it is directly proportional to the surface area, concentration gradient, and membrane permeability

Answer 376

Fick's law states that the diffusion rate increases with an increase in surface area, concentration gradient, or membrane permeability.

Answer 377

-The size and shape of the diffusing molecule: Larger molecules have decreased membrane permeability. -The lipid-solubility of the molecule: Greater lipid solubility increases membrane permeability. -The composition of the lipid bilayer: Alterations in lipid composition affect the ease of molecule passage between phospholipids. For instance, cholesterol molecules in membranes can decrease permeability by occupying spaces between fatty acid tails.

Answer 378

-Facilitated diffusion: This passive process moves molecules down their concentration gradient and ceases when concentrations are equal on both sides of the membrane. -Active transport: This process requires energy from ATP or another outside source and moves substances against their concentration gradient.

Answer 379

-Physiologists prefer to classify membrane proteins by their function rather than their structure. The four broad categories of membrane proteins are: -Structural proteins -Enzymes -Receptors -Transport proteins

Answer 380

-Creating cell junctions that hold tissues together, such as tight junctions and gap junctions. -Connecting the membrane to the cytoskeleton to maintain the shape of the cell. An example of this is seen in the microvilli of transporting epithelia. -Attaching cells to the extracellular matrix by linking cytoskeleton fibers to extracellular collagen and other protein fibers.

Answer 381

The selectivity of a channel is determined by the diameter of its central pore and the electrical charge of the amino acids lining the channel. The open or closed state of a channel is determined by regions of the protein molecule that act like swinging "gates." These gates can be controlled by various factors, including chemically gated channels, voltage-gated channels, and mechanically gated channels.

Answer 382

Open channels spend most of their time with their gates open, allowing ions to move back and forth across the membrane without regulation. Gated channels spend most of their time in a closed state and regulate the movement of ions through them. Gated channels can be chemically gated, voltage-gated, or mechanically gated.

Answer 383

Carrier proteins bind with specific substrates and carry them across the membrane by changing conformation. This mode of transport is much slower than movement through channel proteins. Carrier proteins can transport molecules across a membrane in both directions or restrict their transport to one direction, unlike channel proteins, which create a continuous passage between the inside and outside of the cell

Answer 384

Carrier proteins typically transport small organic molecules (e.g., glucose and amino acids) and ions (e.g., Na+ and K+). They can move solutes and ions into and out of cells, as well as into and out of intracellular organelles like mitochondria.

Answer 385

Carrier proteins can be classified based on the number of molecules they transport and the direction of transport. Uniport carriers move only one kind of molecule, while cotransporters move two or more kinds of molecules. Cotransporters can be further classified as symport carriers if the molecules are transported in the same direction or antiport carriers (aka exchangers) if the molecules are transported in opposite directions.

Answer 386

Carrier proteins can operate through facilitated diffusion or active transport. Facilitated diffusion relies on a concentration gradient for energy, while active transport requires an outside energy source such as ATP or the potential energy stored in a concentration gradient created using ATP.

Answer 387

Polar molecules cross the cell membrane by facilitated diffusion with the aid of specific carrier proteins. These carriers facilitate the movement of polar molecules such as sugars and amino acids across the membrane.

Answer 388

Facilitated diffusion shares the same properties as simple diffusion: the transported molecules move down their concentration gradient, the process requires no input of outside energy, and net movement stops at equilibrium when the concentration inside the cell equals the concentration outside the cell

Answer 389

by keeping the concentration of substrate low inside the cell. For example, with glucose transport, glucose molecules are phosphorylated to glucose 6-phosphate upon entering the cell, which prevents their buildup inside the cell and also prevents glucose from leaving the cell.

Answer 390

Phosphorylation of molecules such as glucose upon entry into the cell prevents their accumulation inside the cell and regulates their movement across the membrane. This process helps maintain concentration gradients and prevents equilibration of substrate concentrations inside and outside the cell

Answer 391

-In primary (direct) active transport, the energy to push molecules against their concentration gradient comes directly from the high-energy phosphate bond of ATP. In secondary (indirect) active transport, the potential energy stored in the concentration gradient of one molecule is used to push other molecules against their concentration gradient. -Secondary active transport ultimately depends on primary active transport because the concentration gradients that drive secondary transport are created using energy from ATP generated by primary active transport.

Answer 392

- Primary active transporters, such as ATPases, use ATP as their energy source to transport molecules against their concentration gradient across the cell membrane. - Primary active transporters are sometimes called pumps because they actively pump molecules across the cell membrane against their concentration gradient using energy derived from ATP hydrolysis.

Answer 393

-The sodium-potassium pump, also known as Na+ K+ ATPase, is a primary active transporter that maintains the concentration gradients of sodium (Na+) and potassium (K+) ions across the cell membrane. It pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell for each ATP consumed. It is crucial for maintaining cell volume, electrical excitability, and various cellular processes. -In some cells, the energy needed to move sodium and potassium ions using the sodium-potassium pump accounts for approximately 30% of all the ATP produced by the cell.

Answer 394

The sodium concentration gradient, with Na+ concentration higher in the extracellular fluid and lower inside the cell, serves as a source of potential energy for various cellular functions. Secondary active transport systems, driven by the sodium concentration gradient, use this potential energy to transport other molecules against their concentration gradient. For example, glucose uptake in epithelial cells is facilitated by the sodium-glucose symporter (SGLT), which couples the movement of glucose into the cell against its concentration gradient with the movement of Na+ ions down their concentration gradient

Answer 395

SGLT transporters, found in certain epithelial cells such as intestinal and kidney cells, facilitate the uptake of glucose from the external environment into the body. They transport glucose into the cell against its concentration gradient by coupling its movement with the downhill movement of Na+ ions. This mechanism allows for efficient glucose absorption from the intestinal lumen and reabsorption in the kidney tubules.

Answer 396

While GLUT transporters are reversible and can move glucose into or out of cells depending on the concentration gradient, SGLT transporters are needed to transport glucose against its concentration gradient, particularly in epithelial cells involved in nutrient absorption. SGLT transporters enable the efficient uptake of glucose from the external environment into the body, whereas GLUT transporters facilitate glucose transport across various tissues depending on metabolic needs

Answer 397

Specificity refers to the ability of a transporter to selectively move only one molecule or a group of closely related molecules across a cell membrane.

Answer 398

The property of competition refers to the ability of different substrates to compete with each other for binding sites on a transporter protein.

Answer 399

Saturation refers to the point at which all carrier binding sites are filled with substrate molecules, resulting in the carriers working at their maximum rate. At saturation, further increases in substrate concentration have no effect on the transport rate because all available carrier molecules are already engaged.

Answer 400

Cells can increase their transport capacity and avoid saturation by increasing the number of carrier molecules in the membrane. This is akin to opening more doors into the concert hall, allowing more molecules to be transported across the membrane per unit time. Additionally, cells may regulate the insertion or withdrawal of carriers in response to changing demands for transport.

Answer 401

Phagocytosis is the process by which a cell engulfs solid particles, such as bacteria or other foreign particles, into a large membrane-bound vesicle called a phagosome. This process is mediated by actin and requires energy from ATP for cytoskeletal movement and intracellular vesicle transport

Answer 402

During phagocytosis, the cell surrounds the particle to be ingested and encloses it within a vesicle called a phagosome. The phagosome then separates from the cell membrane and moves into the cell's interior. Inside the cell, the phagosome fuses with lysosomes containing digestive enzymes, which destroy the engulfed particle.

Answer 403

Endocytosis is a cellular process by which large molecules or particles are engulfed and brought into the cell. It involves the inward indentation of the cell membrane to form vesicles that transport the engulfed material into the cell's interior.

Answer 404

-In endocytosis, the cell membrane indents inward to form vesicles, whereas in phagocytosis, the membrane pushes out to engulf large particles. -The vesicles formed in endocytosis are much smaller than those formed in phagocytosis. -Some forms of endocytosis, known as constitutive endocytosis, occur continuously as an essential cellular function, whereas phagocytosis is triggered by the presence of specific substances.

Answer 405

The two main types of endocytosis are: -Pinocytosis: Nonselective endocytosis in which the cell ingests extracellular fluid along with dissolved solutes. -Receptor-mediated endocytosis: Highly selective endocytosis in which specific molecules, known as ligands, bind to membrane receptor proteins, triggering the internalization of ligand-receptor complexes into the cell.

Answer 406

Receptor-mediated endocytosis begins with the binding of extracellular ligands to their specific membrane receptors. This receptor-ligand complex migrates along the cell surface until it encounters a coated pit. The coated pit invaginates and pinches off from the cell membrane, forming a cytoplasmic vesicle containing the ligand. The clathrin molecules, which are abundant in coated pits, are released and recycled back to the membrane. Inside the vesicle, the receptor and ligand separate, with the ligand enclosed in an endosome. The endosome may then fuse with a lysosome for degradation of the ligand or with the Golgi complex for further processing. The membrane-bound receptors may be recycled back to the cell membrane through membrane recycling. The vesicle containing the receptors fuses with the cell membrane, and the vesicle membrane is incorporated back into the cell membrane through exocytosis, with the extracellular surface of the cell membrane becoming the inside face of the vesicle membrane

Answer 407

Clathrin is the most common protein found in coated pits and plays a crucial role in receptor-mediated endocytosis. It helps in the formation of coated pits by providing structural support and aids in the invagination of the cell membrane to form vesicles. After vesicle formation, clathrin molecules are released and recycled back to the membrane for further use.

Answer 408

-Caveolae are small flask-shaped indentations found on the cell membrane. They contain lipid rafts, membrane receptor proteins, and specialized membrane proteins called caveolins and cavins. Caveolae serve several functions, including concentrating and internalizing small molecules, assisting in the transfer of macromolecules across the capillary endothelium, and participating in cell signaling -The receptors in caveolae are lipid-anchored proteins. They play a role in concentrating and bringing receptor-bound molecules into the cell.

Answer 409

Caveolae are small flask-shaped indentations, while clathrin-coated pits are small depressions on the cell membrane covered with clathrin molecules. Caveolae contain lipid rafts and specialized membrane proteins like caveolins and cavins, while clathrin-coated pits mainly consist of clathrin proteins. Caveolae have been implicated in various cellular processes, including endocytosis, macromolecule transfer, and cell signaling, whereas clathrin-coated pits are primarily involved in receptor-mediated endocytosis

Answer 410

Exocytosis is a cellular process where intracellular vesicles move to the cell membrane, fuse with it, and release their contents to the extracellular fluid. It is the opposite of endocytosis, where substances are taken into the cell via invagination of the cell membrane.

Answer 411

Exocytosis is used by cells to export large lipophobic molecules, such as proteins synthesized in the cell, and to eliminate wastes stored in lysosomes resulting from intracellular digestion.

Answer 412

Exocytosis involves two families of proteins: Rabs, which aid vesicles in docking onto the cell membrane, and SNAREs, which facilitate the fusion of vesicle and cell membranes. The process usually starts with an increase in intracellular calcium concentration, triggering vesicle docking and fusion. When fusion occurs, vesicle contents are released into the extracellular fluid while the vesicle membrane becomes part of the cell membrane

Answer 413

Regulated exocytosis is a process where exocytosis is triggered by a specific signal. It typically begins with an increase in intracellular calcium concentration, which interacts with a calcium-sensing protein to initiate vesicle docking and fusion.

Answer 414

the apical membrane and the basolateral membrane.

Answer 415

The apical membrane is also called the mucosal membrane, while the corresponding term for the basolateral membrane is the serosal membrane.

Answer 416

transporting epithelial cells are said to be polarized because their apical and basolateral membranes have very different properties, including the distribution of certain transport proteins.

Answer 417

The two main routes for movement across an epithelium are paracellular transport through the junctions between adjacent cells and transcellular transport through the epithelial cells themselves

Answer 418

In "tight" epithelia, cell-cell junctions act as barriers to minimize the unregulated diffusion of material between the cells, resulting in very little paracellular transport.

Answer 419

Claudins are junctional proteins that can form large holes or pores in epithelia, allowing water, ions, and a few small uncharged solutes to move by the paracellular pathway.

Answer 420

Transcellular transport involves molecules crossing two cell membranes: one when they move into the epithelial cell and another when they leave the epithelial cell to enter the second compartment. It utilizes a combination of active and passive transport mechanisms.

Answer 421

Cells of transporting epithelia can alter their permeability by selectively inserting or withdrawing membrane proteins. Transporters may be pulled out of the membrane and destroyed in lysosomes or stored in vesicles inside the cell for reinsertion into the membrane in response to a signal.

Answer 422

-SGLT-mediated secondary active transport of glucose with Na+ from the lumen into the epithelial cell at the apical membrane. -Sodium movement out of the cell by primary active transport via a Na+/K+ ATPase. -Glucose leaving the cell by facilitated diffusion on GLUT carriers.

Answer 423

by coupling its transport with the movement of sodium ions. Sodium ions in the lumen bind to the SGLT carrier, bringing glucose with them into the cell. The energy needed for this process comes from the kinetic energy of sodium ions moving down their concentration gradient

Answer 424

The Na+/K+ ATPase is responsible for pumping sodium ions out of the cell against their concentration gradient, creating a sodium concentration gradient that provides the energy for the SGLT-mediated secondary active transport of glucose into the cell.

Answer 425

by moving down its concentration gradient through facilitated diffusion GLUT transporters located in the basolateral membrane

Answer 426

The Na+/K+ ATPase pumps sodium ions out of the cell on the basolateral side, creating a sodium concentration gradient. This process requires energy provided by ATP because sodium is more concentrated in the extracellular fluid than in the cell. The removal of sodium from the cell is essential for the continued absorption of glucose from the lumen.

Answer 427

sodium that enters the cell cannot be pumped out, leading to an increase in intracellular sodium concentration. Without a sodium gradient, there is no energy source to drive the SGLT symporter, and the absorption of glucose across the epithelium stops

Answer 428

Transepithelial transport can use ion movement through channels in addition to carrier-mediated transport. For example, the apical membrane of a transporting epithelium may use the NKCC symporter to bring potassium into the cell against its concentration gradient, using energy from the sodium gradient. Potassium can then move out of the cell on the basolateral side through open potassium leak channels, while sodium must be pumped out by the Na+/K+ ATPase. This mechanism allows the body to absorb sodium and potassium simultaneously from the lumen.

Answer 429

Transcytosis is a process involving a combination of endocytosis, vesicular transport across the cell, and exocytosis. It allows molecules, such as proteins, that are too large to cross epithelia on membrane transporters to be moved across the epithelium while remaining intact.

Answer 430

In transcytosis, the molecule is first brought into the epithelial cell via receptor-mediated endocytosis, forming a vesicle. This vesicle attaches to microtubules in the cell's cytoskeleton and is transported across the cell by vesicular transport. Finally, at the opposite side of the epithelium, the contents of the vesicle are expelled into the interstitial fluid by exocytosis.

Answer 431

The major cation within cells is potassium (K+), while sodium (Na+) dominates the extracellular fluid. Chloride ions (Cl-) mostly remain with Na+ in the extracellular fluid. Phosphate ions and negatively charged proteins are the major anions of the intracellular fluid

Answer 432

Can be used to calculate equilibrium potential for any ion at 37 degrees. Eion = (61/z)(log([ionout]/[ionin]) -where 61 is 2.303 RT/F at 37 °C -z is the electrical charge on the ion ( + 1 for K + ) -(ion) out and (ion) in are the ion concentrations outside and inside the cell, and E ion is measured in mV.

Answer 433

(1) the concentration gradients of different ions across the membrane and (2) the permeability of the membrane to those ions

Answer 434

Membrane potential is monitored using recording electrodes, with the extracellular electrode set at 0 mV. Changes in membrane potential are described as depolarization (when the potential difference becomes less negative), repolarization (return to the resting membrane potential), or hyperpolarization (when the potential becomes more negative).

Answer 435

Small changes in membrane potential act as signals in nonexcitable tissues, such as endocrine cells. These changes regulate cell function by controlling processes like facilitated diffusion, exocytosis, and the opening and closing of ion channels by ligands and membrane potential

Answer 436

by linking the cell's metabolism to its electrical activity. When blood glucose levels increase after a meal, glucose enters the beta cells, stimulating ATP production through glycolysis and the citric acid cycle. Increased ATP closes ATP-gated K+ channels, leading to cell depolarization. Depolarization opens voltage-gated Ca2+ channels, allowing Ca2+ influx and triggering insulin release by exocytosis

Answer 437

Two channels control insulin release from beta cells: voltage-gated Ca2+ channels and ATP-gated K+ channels (KATP channels). At resting membrane potential, KATP channels are open, allowing K+ efflux, and Ca2+ channels are closed, resulting in no insulin secretion. Increased ATP levels, due to higher glucose concentrations, close KATP channels, leading to cell depolarization. Depolarization opens Ca2+ channels, allowing Ca2+ influx and triggering insulin release

Answer 438

Increased blood glucose levels lead to insulin secretion in beta cells by stimulating glucose entry into the cell through GLUT transporters. Inside the cell, glucose undergoes glycolysis and the citric acid cycle, increasing ATP production. Elevated ATP levels close ATP-gated K+ channels, causing cell depolarization. Depolarization opens voltage-gated Ca2+ channels, allowing Ca2+ influx, which triggers insulin release by exocytosis

Topic 1: Chapt 1-5 Flashcards

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