Test de topic 1 y 2 Flashcards
1
Q
water: characteristics
A
-water is a solvent
-water is cohesive
-the oxygen atoms attracts electrons a bit more strongly than the hydrogen atoms
-the unequal sharing of electrons gives the water molecule a slightly negative charge near its oxygen atom and a slight positive charge near its hydrogen atoms
-this causes water to have a permanent dipole- an uneven distribution of charge (one end more positive and another more negative) within the molecules, making water a polar molecule, also because the atoms are held by covalent bonds
-many substances, such as inorganic ions, can dissolve in water thanks to these positive and negative charges within the molecule
-when substances dissolve in water, they can move, allowing chemical reactions to occur
2
Q
carbohydrates: basic info.
A
-carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides
-there are 3 types of saccharides- monosaccharides, dissacharides and polysaccharides
-monosaccharides can join together to form dissacharides and polysaccharides by glycosidic bonds which are formed in condensation reactions
3
Q
monosaccharides:
A
-these are the monomers of carbohydrates
-they are soluble in water and small, simple molecules
4
Q
monosaccharides: glucose
A
-one of the most common monosaccharides is glucose, it contains six carbon atoms in each molecule, it is the main substrate for respiration therefore a very important biological molecule
-isomers of glucose -> a-glucose + b-glucose
-general formula -> (CH2O)n -carbon
-triose: 3 carbons
-pentose: 5 carbons
-hexose: 6 carbons
5
Q
disaccharides:
A
-> 2 monosaccharides join together in a condensation rxn to form a disaccharide
-maltose is a disaccharide formed by the condensation of two glucose molecules (a-glucose)
-surcrose is a disaccharide formed by condensation of b-glucose and fructose
-lactose is a disaccharide formed by the condensation of b-glucose and b-galactose
6
Q
what is a glycosidic bond?
A
-removal of hydrogen atom
-H from one monosaccharide and a hydroxyl group (-OH)
7
Q
polysaccharides: basic info.
A
-> these are formed from many monosaccharides of glucose joined together and are used as energy stores:
-they are a large molecule with a compact shape- there are many glucose molecules within a small space
-they can be easily hydrolysed to glucose-glucose can then be broken down in respiration to release energy
-they are insoluble-so they have no osmotic effect in cells
8
Q
polysaccharides: glycogen
A
-glycogen is the main energy storage molecule in animals and its formed from many molecules joined together by 1,4 and 1,6 glycosidic bonds
-it has a large number of side branches meaning that energy can be released quickly
-moreover, its relatively large but compact molecules thus maximising the amount of energy it can store
9
Q
polysaccharides: starch
A
-starch is the primary energy store in plants and it is a mixture of two polysaccharides called amylose and amylopectin:
-amylose -> amylose is an unbranched chain of glucose molecules joined by 1,4 glycosidic bonds, as a result of this amylose is coiled and this it is a very compact molecule meaning it can store a lot of energy
-amylopectin -> amylopectin is branched and is made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds, due to the presence of many side branches it is rapidly digested by enzymes therefore energy is released quickly
-also, they are large molecules so they have no effect on water potential
10
Q
joining monosaccharides to form disaccharides and polysaccharides:
A
-monosaccharide monomers such as glucose and galactose can join tog through condensation reactions-reactions that joins 2 molecules together through the release of a small molecule (often water)
-the bond formed between 2 monosaccharides is known as a glycosidic bond and contains a single oxygen atom
-to break apart polysaccharides these glycosidic bonds have to be broken, this through a hydrolysis reaction where are water molecule is added, splitting a polysaccharide into 2 smaller molecules, or a disaccharides into 2 monosaccharides
11
Q
lipids:
A
-> lipids are biological molecules that have many different functions within an organism such as energy storage, organ protection, thermal insulation and making cell membrames
-they are non-polar molecules so insoluble in water, but soluble in organic solvents
-lipids can be saturated or unsaturated
12
Q
saturated and unsaturated lipids:
A
-saturated lipids (such as those found in animal fats)- saturated lipids don’t obtain any carbon-carbon double bonds
-unsaturated lipids (these can be found in plants)- unsaturated lipids contain carbon-carbon double bonds and melt at lower temperatures than saturated fats
-mono -> 1 carbon carbon double bond
-poly -> many carbon = carbon double bonds
13
Q
fatty acids and glycerol:
A
-3 fatty acids: COOH carboxyl group
-1 glycerol molecule: -OH
14
Q
forming triglycerides:
A
-triglycerides are one of the most important lipids
-are made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions
-there are many different types of fatty acids, they vary in chain length, presence and number of double bonds
-also, some triglycerides contain a mix of different fatty acids
-triglycerides are used as long term energy reserves in plant and animal cells
15
Q
ester bonds:
A
-condensation reactions
-between carboxyl group (COOH) + hydroxyl group (-OH)
-this is called esterification condensation reaction
-(making esters) -> forms triglycerides
16
Q
proteins:
A
-amino acids are the monomers from which proteins are made
-amino acids contain:
-an amino group- NH2
-a carboxylic acid group
-a variable R group which is carbon-containing chain
17
Q
peptide bonds:
A
-there are 20 different amino acids with different R groups
-amino acids are joined by peptide bonds formed in condensation reactions
-a dipeptide contains two amino acids and polypeptides contain three or more amino acids
18
Q
protein structure: primary structure
A
-> indicated the order of the amino acids
-formed by many amino acid + peptide bonds
19
Q
protein structure: secondary structure
A
-> is the shape that the chain of amino acids fold into-either alpha helix or beta pleated sheet
-the shape is determined by the hydrogen bonding between the peptide bonds
-amino acids interact with eachother
-the H and NH group is attracted to the O on the CO group
-the H is slightly positive and the O is slightly negative
-a hydrogen bond forms between these two atoms
20
Q
alpha helices + beta pleated sheets:
A
-the H-bonds that keep alpha helices together are vulnerable to fluctuations in pH + temperature
-this is how proteins get denatured: their structure is discripted
-hydrogen bonds hold adjacent primary chains together
21
Q
protein structure: tertiary structure
A
-> is the 3D shape of the protein, it can be globular or fibrous
-globular proteins, such as enzymes, are compact
-fibrous proteins, such as keratin, are long and thus can be used to form fibre
-the shape of the protein is determined by hydrogen, ionic and disulphide bonds between the R groups of amino acids
22
Q
protein structure: tertiary structure- disulfide bonds
A
-the amino acid cysteine contains sulfur, where two cysteines are found close to each other a covalent bond can form
23
Q
protein structure: tertiary structure-ionic bonds
A
-R-groups sometimes carry a charge, either +ve or -ve, where oppositely charged amino acids are found close to each other than ionic bond forms
24
Q
protein structure: tertiary structure-hydrogen bonds
A
-as in secondary structure, wherever slightly positively charged groups ate found close to slightly negatively charged groups hydrogen bonds
25
protein structure: tertiary structure- hydrophobic and hydrophilic bonds
-in a water-based environments, hydrophobic amino acids will be most stable if they are held together with water excluded
-hydrophilic amino acids tend to be found on the outside in globular proteins with hydrophobic amino acids in the centre
26
protein structure: quaternary structure
-> some proteins have a quaternary structure, this is when 2 or more polypeptide chains are joined together, sometimes with the addition of a non-protein prosthetic group
27
collagen:
-> is a fibrous protein of great strength due to presence of both hydrogen and covalent bonds in its structure
-collagen molecules wrap around each other and form fibrils which form strong collagen fibres
-collagen forms the structure of bonds, cartilage and connective tissue and is a main component of tendons which connect muscles to bones
28
haemoglobin:
-> is a water soluble globular protein which consists of two beta polypeptide chains,2 alpha polypeptide chains and 4 haem groups
-it carries oxygen in the blood as oxygen can bind to the haem (Fe2+) group, and oxygen is then released when required
-haemoglobin is made up of 4 polypeptide chains as well as 3 prosthetic groups, so it has a quaternary structure
29
formula for area:
length x height x sides
30
formula for volume:
length x width x height
31
why we need a transport system:
-diffusion in single-celled organisms can occur directly between the external environment and the cell, this is known as simple diffusion as it occurs only through the cell membrane
-exchange of substances, such as oxygen for these organisms occurs very quickly as they have a very large surface area: volume ratio
-for larger organisms, like us humans, we have low surface area: volume ratio, meaning diffusion would be too slow to supply all cells with the nutrients they need and this is why larger organisms have mass transport systems that supply all cells with vital substances
32
circulatory system:
-the mammalian circulatory system is comprised of the heart and three types of blood vessels: arteries, veins and capillaries
-each blood vessel is adapted to its role in the circulation of the blood
33
arteries:
-arteries carry oxygenated blood away from the heart
-this vessel has thick walls containing muscles and elastic that expand and recoil with each heartbeat to withstand the high pressure of the blood
-they have a relatively small lumen (hole in the centre through which the blood passes)
-arteries contain no valves
-its inner lining is folded to allow it to stretch
-arteries split into smaller blood vessels called arterioles which split into capillaries
-they are lined with smooth endothelium to reduce friction and ease flow of blood
34
capillaries:
-arterioles branch into these to supply cells with substances from the blood
-they are numerous and highly branched so have a large surface area
-their walls are one cell thick to allow quick diffusion
-very narrow diameter to reach close to every cell
35
veins:
-capillaries join back up to form these, so veins carry deoxygenated blood back to the heart
-carry blood a low pressure to have thin walls
-have a wide lumen to maximise blood flow to the heart
-have valves to prevent backflow (blood flowing in the wrong direction)
36
structure of the heart:
-the heart is comprised of 4 chambers: the left and right atria and the left and right ventricles
-the atria receive blood into the heart from the veins
-the ventricles pump blood out of the heart via the arteries to the lungs or the body
-between the ventricles and the atria are the atrioventricular valves which prevent blood flowing back from the ventricles and into the atria; between the ventricles and the arteries leaving the heart are the semilunar valves which prevent backflow of blood from the arteries into the ventricles
37
a double circulatory system:
-mammals are described as having a ‘double circulatory system’, this is because the blood flows through the heart twice in each circulation
-blood first enters the heart into the right atrium through the largest vein in the body- vena cava
-the first time it leaves the heart it travels from the right ventricle via the pulmonary artery to the lungs where it becomes oxygenated, the blood then returns to the heart via the pulmonary vein into the left atrium
-the second time the blood leaves the heart is from the left ventricle via the aorta, where blood now flows to the rest of the body
38
the cardiac cycle:
-the movement of blood through the heart is carefully controlled by the contracting and relaxing of heart muscles, the cardiac cycle has three stages as follows:
1. Atrial systole
2. Ventricular systole
3. Cardiac diastole
39
the cardiac cycle: atrial systole
-the atria contract and this forces the atrio-ventricular valves open and blood flows out of the atria and into the ventricles
-pressure in the atria is greater than in the ventricles, so blood is forced out
40
the cardiac cycle: ventricular systole
-the ventricles then contract, causing the atrio-ventricular valve to open and close and semi-lunar valves to open
-thus allowing blood to leave the left ventricle through the aorta and right ventricle through the pulmonary artery
41
the cardiac cycle: cardiac diastole
-the atria and ventricles relax, elastic recoil of the heart lowers the pressure inside the heart chambers and blood is drawn from the arteries and veins
-thus causing semilunar valves in the aorta and pulmonary arteries to close, preventing backflow of blood
42
transport of gases in the blood: haemoglobin
-haemoglobin is a water soluble globular proteins found in red blood cells, which consists of two beta polypeptide chains, 2 alpha polypeptide chains and 4 haem groups
-each of the 4 polypeptide chains is bound to a haem group (Fe2+) to which 1 oxygen molecule can bind
-this means each molecule of haemoglobin can carry 4 oxygen molecules
-the oxygen binds with haemoglobin to form oxyhaemoglobin, and can unbind when needed in respiring cells and tissues
43
transport of oxygen and carbon dioxide:
-the affinity of oxygen for haemoglobin (how easily oxygen loafs onto haemoglobin) varies depending on the partial pressure of oxygen, which is a measure of oxygen concentration
-therefore, as partial pressure increases, the affinity of Hb for oxygen increases
-this means that oxygen binds to Hb more readily
-this occurs in the lungs in the process known as loading
-during respiration, oxygen is used up therefore the partial pressure decreases, decreasing the affinity of oxygen for Hb
-as a result of that, oxygen is released from Hb in respiring tissues where it is needed; this is known as unloading
-as oxygen diffuses into respiring tissues for respiration, carbon dioxide diffuses out and into the capillaries
-here, the low partial pressure of oxygen environment, carbon dioxide binds to Hb to form carboxyhaemoglobin
-the deoxygenated blood returns to the lungs where carbon dioxide unloads from Hb, which binds to oxygen again
44
dissociation curves:
-dissociation curves illustrate the change in haemoglobin saturation as partial pressure changes
-the saturation of haemoglobin is affected by its affinity for oxygen, therefore in the case where partial pressure is high, Hb has high affinity for oxygen and is therefore highly saturated, and vice versa
45
factors resulting in different affinities: saturation
-saturation can also have an effect on affinity, as after binding to the first oxygen molecule, the affinity of Hb for oxygen increases due to a change in shape, this making it easier for the other oxygen molecules to bind
46
factors resulting in different affinities: fetal haemoglobin
-the haemoglobin present in foetuses has a different affinity for oxygen compared to adult haemoglobin, as it needs to be better at absorbing oxygen because by the time oxygen reaches the placenta, the oxygen saturation of the blood has decreased
-therefore, fetal haemoglobin must have a higher affinity for oxygen in order for the foetus to survive at low partial pressure
47
factors resulting in different affinities: the Bohr effect
-the affinity of Hb for oxygen is also affected by the partial pressure of carbon dioxide
-carbon dioxide is released by respiring cells, which require oxygen for the process to occur
-therefore, in the presence of carbon dioxide, the affinity of haemoglobin for oxygen decreases, thus causing it to be released
48
astherosclerosis:
-astherosclerosis is the hardening of arteries cause by the build up of fibrous plaque called an atheroma
-atheroma formation is the cause of many cardiovascular diseases and occurs as following:
1. The endothelium which lines the arteries is damaged, for instance by high cholesterol levels, smoking or high blood pressure
2. This increases the risk of blood clotting in the artery and leads to an inflammatory response causing white blood cells to move into the artery
3. Over time, white blood cell, cholesterol, calcium salts and fibres build up and harden leading to a plaque formation
4. The build up of fibrous plaque leads to narrowing of the artery and restricts blood flow thus increasing the blood pressure which in turn damages the endothelial lining and the process is repeated
49
blood clotting:
-blood clots are formed to minimise blood loss from damaged vessels, and also to prevent pathogens entering the bloodstream
-blood clots are important to preventing damage to the body, however when they form on the inside of blood vessels, they can restrict blood flow through the vessels and cause a blockade
-this is known as thrombosis and can cause cardiovascular disease, blood clots are formed as follows:
1. Platelets come into contact with a damaged blood vessel wall and change shape from flattened discs to spherical shapes with thin outward projections which form a temporary plug by clumping together
2. The platelets and damaged tissues release clotting factors such as thromboplastin which causes prothrombin to change to thrombin
3. This enzyme catalyses the conversion of fibrinogen to insoluble fibrin, whose strands form a mesh, trapping bundles of blood cells, more platelets attach to this, forming the clot
50
the effects of astherosclerosis on health: aneurysms
-weakened artery walls
-bulging of artery wall (may rupture)
-commonly occurs in the aorta
-potentially life-threatening if ruptured
51
the effects of astherosclerosis on health: raised blood pressure (hypertension)
-narrowed arteries restrict blood flow
-increased resistance to blood flow
-heart must work harder
-risk factor for other cardiovascular events (heart attacks, strokes)
52
the effects of astherosclerosis on health: heart disease
-Angina:
-reduces blood flow to the heart
-chest pain (especially during exertion)
-temporary, typically relieved by rest
-Myocardial infarction (heart attack):
-complete blockage of coronary artery
-heart muscle deprived of oxygen
-permanent damage to heart tissue if not treated quickly
-symptoms include sever chest pain, shortness of breath, sweating
53
the effects of astherosclerosis on health: stroke
-blocked or ruptured arteries in the brain
-ischemic stroke: blood clot obstructs blood flow to brain
-hemorrhagic stroke: burst blood vessel in the brain
-symptoms include sudden weakness, slurred speech, confusion, loss of coordination
-can lead to permanent disability or death
54
dietary antioxidants: (oxidative stress)
-oxidative stress is an imbalance of antioxidants and free radicals of oxygen in the body
-free radicals of oxygen are oxygen atoms with an uneven number of electrons, making it highly reactive and meaning it can cause damaging chains of chemical reactions in the body
-antioxidants can donate electrons to make oxygen radical stable, without making itself unstable
-it’s thought that this oxidative stress can contribute towards the cause of cardiovascular disease, so the intake of additional antioxidants in the diet should help prevent some cases of CVDs and at least lessen the risk
55
DCPIP: experiment
-volume of fluid needed to decolourise the solution
-6mg (example) divided by volume needed to turn colourless gives appoximate concentration of Vitamin C
-which we can compare to toher results
-need total colour change
56
blood cholesterol levels and CVD:
-cholesterol is transported in your body in high-density lipoproteins (HDLs) or low-density proteins (LDLs), they each have different effect on cholesterol levels and are found in different types of food
-there is a positive correlation between ingestion and saturated fats and an increase in cholesterol level
-since increased cholesterol levels cause a build-up of plaque on artery walls, there is a casual relationship between saturated fats (LDLs) and cardiovascular disease
57
high-density lipoproteins:
-transports cholesterol to the liver to be expelled
-reduces cholesterol levels
-the more of this you have in your body, the better
-formed from unsaturated fats and proteins
58
low-density lipoproteins:
-transports cholesterol to the arteries where it can build up and form plaque
-increases cholesterol levels
-the less you have of this in your body, the better
-formed from saturated fats and proteins
59
treatment of cardiovascular diseases: antihypertensives
-> these are drugs that are used to lower blood pressure
-pros: generally effective on most patients and inexpensive
-cons: different types of drugs have different side effects, although most aren’t severe and are irreversible
60
treatment of cardiovascular diseases: statins
-> these are a class of drugs used to lower cholesterol levels and so reduce the build-up of plaques on artery walls
-pros: mostly effective, also help relax blood vessels leading to a lower blood pressure, also helping to prevent CVD
-cons: can cause nausea, vomiting and aches in muscles and joints, as well as more severe but less common side effects such as diabetes, the side effects often go away over time
61
treatment of cardiovascular diseases: anticoagulants
-> these are drugs that help prevent blood clots
-pros: reduce the risk of internal blood clots that can sometimes cause thrombosis and reduce blood flow in the artery
-cons: can, like anticoagulants, also lead to excessive bleeding and haemorrhage due to slow clot formation
62
body mass index (BMI):
BMI = body mass kg/ (body height (m))^2
-the value generated can be compared to a charge which classifies you under the following:
-under 18.5 -> underweight
-18.5-25 -> normal
-25-30 -> overweight
-over 30 -> obese
63
waist to hip ratio (WHR):
-WHR is another way to view if someone is overweight and can also be used to view the risk of developing certain diseases
-you are classified as obese if as a male you have a value greater than 0.8 and as a female a value greater than 0.85
Waist size (cm)/ hip size (cm)
64
lipoproteins:
-fats are not water soluble and cannot be transported in the blood
-the liver creates lipoproteins to carry lipids
-they are like vessels- a submarine- that transports triglyceride to the tissue where it can be oxidised for energy during respiration, or stored
-once the fat has been ‘deposited’ lipopoteins return to the liver to be recycled
-protein and cholesterol molecules on the membrane allow uptake of lipoproteins into tissue
65
ldl:HDL
-more recent research has pointed to the balance of these lipoproteins in the blood and the risk of developing astherosclerosis
-genes have an influence on the ability to metabolise fats in a healthful way
-lower LDL:HDL ratio is a better indicator for reduction in aestherosclerosis and CVD
-higher LDL:HDL ratios are associated with an increased risk of CVD’s
66
exchange surfaces:
-multicellular organisms require gas exchange systems in order to obtain sufficient oxygen for respiring cells, and to expel the carbon dioxide created by these cells
-in order to maximise the rate of exchange of substances, gas exchange surface are adapted to have a:
-large surface area:volume ratio- the larger the ratio, the greater the surfacearea for the organism to carry out exchange, so a faster transfer of substances across the surface
-short diffusion pathway- a short distance for substance to move across means they move faster
-steep concentration gradient- a large difference in concentrations between 2 areas means diffusion of particles from an area high concentration to an area of lower concentration occurs faster
67
Fick’s Law:
-the rate of diffusion is also dependent on the main features
-this is shown by Fick’s law that states that the rate of diffusion is proportional to the surface area multiplied by difference in concentration, divided by the length of diffusion pathway
Rate of diffusion (a) surface area x concentration difference/distance
68
the mammalian lung:
-when we breathe, air enters the mouth, passes into the trachea which splits into 2 bronchi; one on the left side and one on the right side of the body
-each broncus branches out into smaller bronchioles which end in tiny air sacs called alveoli, where gas exchange takes place
-deoxygenated blood flows into the alveoli, where carbon dioxide diffuses out of the capillary, through the alveolar membrame and into the surrounding air, down a concentration gradient
-oxygen moves in the opposite direction from the surrounding air and into the blood steam, making the blood oxygenated
69
the mammalian lung: alveoli adaptations
-the extensive branching of vessels in the lungs means there are many alveoli-over 300 million in an average adult- this gives them a very large surface area which increases the rate of diffusion of oxygen into the blood, and carbon dioxide out of the blood
-the alveoli are adapted further, they have a rich blood supply from surrounding capillaries which mantains a steep concentration gradient between the blood in the capillaries and the air entering the lungs, which again increases the rate of diffusion
-alveoli also have a moist outer lining, allowing gases to dissolve and move across their membrame faster
-finally, alveoli have a wall of only one cell thick and pores in the endothelium, this creates a short distance for the gases to travel over so they can diffuse quickly
70
cell membrames: structure
-all cells and organelles are surrounded by a partially permeable membrame composed of a sea of phospholipids with protein molecules between the phospholipid molecules
-the main function of the membrame is controlling the movement of substances in and out if the cell/organelle
-however, it also contains receptors for other molecules, such as hormones, and enables adjacent cells to stick together
-the main structure of a membrame is the phospholipid bilayer-2 rows of phospholipids (lipids made from 1 molecule of glycerol, 1 phosphate group and 2 fatty acid chains)
-the phosphate groups are hydrophilic (water loving), so form the outside of the bilayer
-whereas fatty acid chains are hydrophobic (water hating), so lie in between the 2 rows of phosphate heads
-the fatty acid chains ae non-polar, allowing non-polar molecules like carbon dioxide to pass straight through the phospholipid bilayer
-while polar substance, like water, have to move though channel proteins, since they aren’t soluble in the fatty acid tails
-cholesterol molecules are also found in the bilayer, these give the membrame stability and reduce its fluidity
71
Fluid Mosaic Model:
-the fluid mosaic model is the name given to the model suggested for the structure of the cell membranes
-it is described as ‘fluid’ due to the fluidity of the phospholipid bilayer which allows all molecules to movel freely within it
-the cell membrame also contains a ‘mosaic’ of transport proteins, receptor proteins, enzymes, structural and recognition proteins of varying shapes and sizes
-cholesterol molecules are also found in the bilayer, these give the membrame stability and reduce its fluidity
-scientific models such as this one are based on data and results of investigations by scientists
-models like this may be update over time, the way the model of the atom was updated numerously, as new data and discoveries are made
72
transport of substances:
-the movement of molecules through cell membrane depends on the properties of the molecule (for instance its size and whether its polar or nonpolar) as well as the requirements of the cell
-movement can be passive (require no energy) or active (requires energy released from respiration)
73
transport of substances: diffusion
-> is the passive movement of molecules down a concentration gradient, from an area of high concentration to an area of lower concentration through a partially permeable membrame
-these are specific types of diffusion- simple diffusion, facilitated diffusion and osmosis
74
transport of substances: simple diffusion
-> is the passive movement of small, non-polar lipid soluble molecules, such as carbon dioxide and oxygen, from an area of high concentration to an area of low concentration
-the molecules move directly through the phospholipid bilayer
75
transport of substances: facilitated diffusion
-> requires a membrame protein to transport polar molecules, charged and water soluble molecules across the membrame
-since these molecules cannot pass through the non-polar inside of the bilayer
76
transport of substances: active transport
-> can transport all types of molecules through carrier proteins from an area of low concentration to an area of high concentration
-this process moves particles against the concentration, and so requires energy in the form of ATP
77
transport of substances: exocytosis + endocytosis
-> transport large particles
-the particles are enclosed in vesicles made from the cell surface membrane and transported into the cell/ organelle in endocytosis
-in exocytosis, vesicles containing large particles are fused with the membrane and leave the cell/organelle
78
osmosis: a special type of diffusion
-> is the net diffusion of water molecules from an area of higher water potential to an area of lower water potential, through a partially permeable membrane
-in the case of osmosis, ‘water potential’ is used to describe the relative concentration of water molecules
-water potential is the tendency of a solution to gain or lose water
-a high water potential means there is a low concentration of solute, in other words a high concentration of water
-pure water has the highest water potential possible
-water potential is measured in pascals, pure water has a value of 0 pascals and all other values are negative, as water potential becomes lower
79
osmosis: isotonic, hypetonic and hypotonic
isotonic: solutions have equal osmotic pressures, so there is not net water movement, and the size of the cell remains the same
-hypotonic: solutions have a lower osmotic pressure, so water will enter the cell, and the cell will swell
-hypertonic: solutions have a high osmotic pressure, so water will leave the cell, and the cell will shrink
80
membrame proteins:
-carrier proteins: can move particles through the membrame by both active transport and facilitated diffusion
-channel proteins: forms pores in the membrame for polar particles to move through by facilitated diffusion
-extrinsic proteins: a membrame protein that goes through only 1 layer of the bilayer
-intrinsic proteins: a membrame protein that goes through both layers of the bilayer
81
enzymes:
Enzymes are biological catalysts that increase the rate of reaction by lowering the activation energy (the energy needed for a reaction to
occur) of the reactions they catalyse, including both intracellular (within cells) and extracellular (outside the cells) reactions
-part of the enzyme is known as the active site, this is where the reaction with the substrate takes place
-since the enzymes are proteins, they have a very specific 3D shape due to the bonding in their tertiary structure
-this means enzymes have a specific and complementary shape to the substrate they bind to, meaning that only one type of substrate fits into the active site of the enzyme
-when the enzyme and substrate form a complex (an enzyme-substrate complex), the tertiary structure of the enzyme is altered so that the active site of the enzyme fits around the substrate
-this is called the induced fit model
-once an enzyme-substrate complex is formed and there is sufficient energy, the reaction can take place, often breaking down the substrate or combining 2 to build up larger molecules
82
nucleotides:
-both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are polymers of nucleotides which consist of:
1. A Penrose sugar - a 5 carbon sugar
2. A nitrogen contIning organic base
3. A phosphate group
-nucleotides join together by phosphodiester bonds formed in condensation reactions
-the phosphodiester bonds are formed between the phosphate groups and a carbon on the pentose sugar of adjacent nucleotides
83
Nucleotides: DNA
-the components of a DNA nucleotide are a pentose sugar called deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine
-adenine and guanine both have double ring structure and are classified as purine bases
84
Nucleotides: RNA
-the component of an RNA nucleotide are a pentose sugar called ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil
-thymine, uracil and cytosine all have single ring structure and are classified as pyramidine bases
85
Complementary base pairing:
--a DNA molecule is a double helix composed of 2 polynucleotides chains running antiparallel to each other, joined together by hydrogen bonds between the 2 strands
-2 hydrogen bonds form between the complementary bases adenine and thymine, and 3 hydrogen bonds form between the complementary bases cytosine and guanine
-this bonding is essential for DNA to maintain a stable structure, as it prevents the chemical bases being corrupted by other outside chemicals or forces
-the bonding is also what twists the strand into the double helix shape
-RNA is a single-stranded polynucleotide chain, so does not have hydrogen bonding between the bases within it, however its bases are still complementary to each other- cytosine and guanine, and adenine and uracil are complementary
86
DNA replication: and the process
-the semi-conservative replication of DNA ensures genetic continuity between generations of cells, meaning that genetic information is passed on from one generation from the next
-the process is described as ‘semi-conservative’ because each strand formed contains 1 new strand, and 1 original strand
-the steps of semiconservative replication of DNA are as follows:
1. The double helix unwinds and the enzyme DNA Helicase breaks the hydrogen bonds between the complementary bases, separating the two strands of DNA
2. One of the strand is used as the template and complementary base pairing occurs between the template strand and free nucleotides that attach to the exposed strands
3. The enzyme DNA polymerase moves along the strands, joining the adjacent nucleotides by forming phosphodiester bonds in condensation reactions
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Meselson and Stahl’s experiment:
2 scientists names Matthew Meselson and Franklin Stahl did an experiment to prove that DNA is replicated semi-conservatively, this is what they did:
1. They began by growing bacteria in a broth containing only one isotope of nitrogen- Nitrogen-15, a heavier isotope than the more abundant Nitrogen-14
-after allowing the bacteria to grow and take the heavy nitrogen into their DNA they isolated the DNA and centrifuged it; the DNA settles at a point equal to it’s density
2. The bacteria containing only ^15N DNA were transferred to a broth now only containing a ^14N medium
-since DNA replicates semi-conservatively, after the first replication of DNA, each double helix contained 1 ^14N strand, and 1 ^15 strand, so settled at a different point when centrifuged
-the scientists observed this was between the settling points of ^15N only DNA, and ^14N only DNA, so concluded the DNA must contain one strand of each
3. They then carried out a second replication of the DNA, still in the ^14N medium, the results of the centrifuge conformed the semi-conservative hypothesis still, with half of the DNA settling out at the ^14N only point, and half of the DNA settling with a combing ^14N and ^15N point
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The genetic code:
the order of nucleotide
bases on DNA makes up the genetic code which consist of triplets of bases; each triplet of bases codes for a particular amino acid and is known as a codon
-for instance, the codon GCA codes for the amino acid alanine
-in ribosomes during protein synthesis the amino acids are joined together by peptide bonds and form a polypeptide chain
-therefore, a gene is a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain
-however, not all of the genome codes for proteins-the non-coding sections of DNA are called introns and the coding regions are called exons
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Features of the genetic code:
-the genetic code is-overlapping meaning that each triplet is only read once and triplets don’t share any bases
-genetic code is also degenerate meaning that more than one triplet codes for the same amino acid, this reduces the number of mutations which are mistakes in the base sequence such as base deletion, insertion or substitution
-for instance, GCA, GCC, GCG, and GCU all code for the amino acid alanine
-the genetic code contains start and stop codons which either start or stop protein synthesis
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Protein synthesis:
-there are 2 stages which convert the sequence of bases on DNA into a polypeptide chain; the DNA must first be copied into mRNA (transcription) which then leaves the nucleus and travels to a ribosome
-this is where the RNA is read and translated into amino acids which are joined to make a polypeptide (translation)
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Protein synthesis: Transcription
-during transcription, a molecule of mRNA is made in the nucleus:
1. The enzyme RNA polymerase attaches to the DNA at the start of the gene (which is signified by a start codon), it breaks the hydrogen bonds between the complementary bases that hold the 2 strands together, this uncoils and separates the 2 strands so they are exposed
2. One of the DNA strands is used as a template to make the mRNA molecule, the template is called the antisense strand
3. RNA polymerase lines up free nucleotides which attach to the template strand by complementary base pairing; adjacent nucleotides are joined by phosphodiester bonds, thus forming a single-stranded molecule of mRNA
4. Once the RNA polymerase reaches a stop codon, the mRNA detaches from the template strand, it then moves out of the nucleus through a pore and attaches to a ribosome in the cytoplasm, which is the site of next stage of protein synthesis called translation
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Protein synthesis: Translation
-during translation, a polypeptide sequence is translated from the mRNA strand:
1. mRNA attaches to a ribosome and transfer RNA collect amino acids from the cytoplasm and carries them to the ribosome, tRNA is a single stranded molecules with an amino acid (Methionine) bind site at one end (so it can only carry one type of amino acid), and a triplet of bases the other (called an anticodon) which is complementary to a triplet of bases on the mRNA strand (the codon) produced during transcription
2. The tRNA molecule attaches itself to mRNA by complementary base pairing-within the ribosome two molecules of RNA attach to the mRNA strand at a time
3. The amino acids attaches to two the tRNA molecules join by forming a peptide bond; then the tRNA molecules detach themselves from the amino acids, leaving them behind as more amino acids attach to the chain
4. This process is repeated leading to the formation of a polypeptide chain until a stop codon is reached on mRNA, which ends the process of protein synthesis
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Types of RNA:
-mRNA (messenger): carries the information (sequence) to produce a protein from a gene
-rRNA (ribosomal): is part of ribosome, which are ribonucleoproteins (protein+DNA)
-tRNA (transfer): carries the amino acids
