Bio/Biochem Flashcards

Question

What is Sphingomyelin?

Answer 1

Sphingomyelin is a glycolipid with a sphingosine backbone in place of the glycerol that is found in phospholipids and glycoglycerolipids. Sphingomyelin clusters with cholesterol to make lipid rafts, which modulate membrane fluidity and serve as organized clusters for various signaling processes.

Answer 2

Glyceroglycolipids are a glycolipid type, which is a major class of membrane lipids. Glyceroglycolipids are similar to phospholipids in that they have a glycerol backbone and two fatty acid tails. However, glyceroglycolipids replace their phosphate group with a carbohydrate group.

Answer 3

Peripheral proteins form temporary bonds with the cell membrane, allowing them to detach and reattach at specific times, with specific signals. This allows cells to coordinate and communicate using networks of proteins and reactions. Peripheral proteins are found within the cytoplasm and are temporarily attached to integral proteins or are associated with lipid bilayer's peripheral regions. They tend to interact only briefly with the membrane before resuming their function in the cytoplasm. **This category includes some enzymes and hormones.** One example is aquaporin, the water transporter. The peripheral proteins can attach to the membrane surface by ionic interactions with an integral membrane protein (or another peripheral membrane protein) or by interaction with the polar head groups of the phospholipids.

Answer 4

Cholesterol helps prevent phospholipids from extreme stacking or motion: In cold temperatures, the hydrophobic tails of lipids will bunch together. Cholesterol with its four-ring structure that gives it a very different, bulky, rigid, and short shape in comparison to the long, skinny, flexible fatty acid tails physically obstructs the tight packing of lipid tails. Therefore, cholesterol promotes membrane fluidity at low temperatures. At high temperatures, the phospholipids move energetically increasing membrane fluidity. Cholesterol physically obstructs phospholipids from extreme motion with its large, bulky structure. In this way, cholesterol ensures membrane fluidity does not detrimentally increase.

Answer 5

No, while both glyceroglycolipids and sphingolipids have hydrophobic tails, glyceroglycolipids do not form lipid rafts with cholesterol. **ONLY** Special sphingolipid **sphingomyelin** clusters with cholesterol molecules to form structures known as “lipid rafts”, which modulate membrane fluidity and various signaling processes.

Answer 6

**Yes**, they are called **Cerebrosides** and **Gangliosides.** And again, you have your standard cell communication lipids, Glyceroglycolipids, which are amphipathic, modified with a carbohydrate group, and that they’re broadly involved in cell signaling and adhesion processes, in addition to being important plasma membrane components.

Answer 7

Glycoproteins are proteins attached to an oligosaccharide group. Many important proteins throughout the body are actually glycoproteins or are glycosylated. Examples include the major histocompatibility complex and the antigens of the ABO blood type system. Not surprisingly, membrane glycoproteins are often involved in cell recognition and communication processes.

Answer 8

**Lipid-anchored proteins** are covalently bound to single or multiple lipid molecules. This arrangement anchors the protein within the membrane, without having it actually touch the membrane itself. **G proteins** are intracellular membrane-bound structures that help coordinate the signaling cascade initiated by the G protein-coupled receptors.

Answer 9

Floppases move phospholipids from the inner leaflet to the outer leaflet. Flippases move phospholipids from the outer leaflet to the inner leaflet.

Answer 10

Yes, as temperature increases, membrane fluidity increases. Membrane fluidity makes some space for molecules to diffuse through the membrane, increasing diffusion. Increasing temperature is the simplest approach to help improve diffusion rates because an increase in temperature will cause the membrane to become more fluid.

Answer 11

Rigidity of phospholipids at low temperature is based on hydrophobic tails bunching up together. Cholesterol increases membrane fluidity by preventing the linear fatty acid tails from packing tightly.

Answer 12

Diffusion is the process of molecules moving from an area of higher concentration to an area of lower concentration until equilibrium is reached so the concentration of solute throughout the solution is even.

Answer 13

The osmosis equation is: π = iMRT 4 Osmoles, 1M Mg and 3 - 1MCl ions.

Answer 14

Osmolarity is like molarity, except that it takes into account ALL solute particles. Magnesium chloride will dissociate to form three ions - two chloride anions and one magnesium cation in solution. The osmolarity will be 2M MgCl2 x 3 particles/ MgCl2 molecule = 6 osmoles.

Answer 15

Facilitated diffusion is passive transport, as no ATP is used either directly or indirectly. This describes secondary active transport because ATP is consumed and the energy is stored as an ion concentration gradient for later use. Both osmosis and facilitated diffusion are driven by differing concentration gradients across a membrane.

Answer 16

Primary and Secondary An example of active transport is the sodium-potassium pump.

Answer 17

Yes. Secondary active transport is a combination of active and passive transport. The active transport generates a concentration gradient that powers the passive transport of something else. Antiporters move two solute types in opposite directions. One solute moves with its concentration gradient and the other moves against its own concentration gradient.

Answer 18

Properties of endosomes include: 1. Endosomes are bound to the plasma membrane on the intracellular side. 2. Endosomes identify receptors that should be sent back to the plasma membrane. 3. Endosomes are organelles.

Answer 19

Phagocytosis is the ingestion of solid particles. Pinocytosis is the ingestion of large quantities of liquids or solutes. Receptor-mediated endocytosis is the ingestion of specific molecules, like iron, from the extracellular environment.

Answer 20

Osmosis deals with the movement of solvent molecules, not solute molecules. Water is a solvent that can diffuse across the plasma membrane through aquaporins (channel proteins specific to water transport) via facilitated diffusion.

Answer 21

Primary active transport requires energy, which can be in the form of ATP hydrolysis, but can also be from other sources such as redox reaction or light. Therefore, ATP consumption is not a requirement of primary active transport.

Answer 22

Yes. In Primary Active Transport a protein channel is needed to carry out this function.

Answer 23

Proton pumps of the electron transport chain are powered by redox reactions, not ATP hydrolysis.

Answer 24

Secondary active transport is powered by concentration gradients that have been established by primary active transport.

Answer 25

Both symporters and antiporters are examples of secondary active transport, but only antiporters will always promote movement of molecules into the cell. Symporters and antiporters use secondary active transport, as they do not directly consume energy. Both allow molecules to move down their concentration gradients to harness their energy to power an unfavorable transport task. More specifically, the spontaneous transport of one substance (usually an ion) down its electrochemical or concentration gradient is coupled to the non-spontaneous transport of another substance against its gradient. Both symporters and antiporters can move molecules into the cell.

Answer 26

Specific molecules, like low-density lipoproteins, are taken in through receptor-mediated endocytosis.

Answer 27

Lysosomes are responsible for degrading ingested substances via endocytosis in order for the cell to repurpose the basic building blocks of the ingested material for other uses.

Answer 28

Late endosomes are responsible for the identification and transport of substances that have been ingested via endocytosis and need to be degraded by lysosomes. However, late endosomes are not responsible for the actual degradation themselves.

Answer 29

The primary difference between facilitated diffusion and passive diffusion is the presence of a protein channel with facilitated diffusion. Facilitated diffusion does not require any energy (either directly or indirectly) and nor does passive diffusion. Both rely on diffusion, which is the tendency of molecules to spread out and their concentrations throughout a solution to equilibrate. Facilitated diffusion is passive diffusion through a protein channel to helps very polar molecules cross the hydrophobic plasma membrane core.

Answer 30

The prokaryotic genome is a small, circular, double-stranded DNA genome.

Answer 31

In prokaryotes, the ETC is located in the cell membrane.

Answer 32

Ionizing radiation damages nucleic acids and leads to mutations. As viruses depend on intact nucleic acids for their genetic information, it is unlikely that CJD has a viral cause. Peptide bonds are less affected by ionizing radiation. One hallmark of prion proteins is their thermodynamic stability.

Answer 33

Tubes 2 and 4.

Answer 34

The bacteria are obligate (strict) aerobes that cannot grow without an abundant supply of oxygen. Tube B looks like the opposite of tube A. Bacteria grow at the bottom of tube B. Those are obligate anaerobes, which are killed by oxygen. Tube C shows heavy growth at the top of the tube and growth throughout the tube, a typical result with facultative anaerobes. Facultative anaerobes are organisms that thrive in the presence of oxygen but also grow in its absence by relying on fermentation or anaerobic respiration, if there is a suitable electron acceptor other than oxygen and the organism is able to perform anaerobic respiration. The aerotolerant anaerobes in tube D are indifferent to the presence of oxygen. They do not use oxygen because they usually have a fermentative metabolism, but they are not harmed by the presence of oxygen as obligate anaerobes are. Tube E on the right shows a “Goldilocks” culture. The oxygen level has to be just right for growth, not too much and not too little. These microaerophiles are bacteria that require a minimum level of oxygen for growth, about 1%–10%, well below the 21% found in the atmosphere.

Answer 35

The lytic cycle, which is also referred to as the "reproductive cycle" of the bacteriophage, is a six-stage cycle. The six stages are: attachment, penetration, transcription, biosynthesis, maturation, and lysis.

Answer 36

The lysogenic cycle is a method by which a virus can replicate its DNA using a host cell. Typically, viruses can undergo two types of DNA replication: the lysogenic cycle or the lytic cycle. In the lysogenic cycle, the DNA is only replicated, not translated into proteins.

Answer 37

A retrovirus consists of RNA that is later reverse-transcribed into DNA and then integrated into the host genome. From there, the host cell machinery transcribes that DNA into mRNA. Thus, the mRNA of the transcribed viral DNA should be identical to the actual viral genome.

Answer 38

4-8 base pairs, DNA, Palindromic with respect to the complement (i.e. TTGCAA) 4-8 base pairs - Restriction sites, palindromic sites are restriction enzymes cleave, are typically around four to eight base pairs long. DNA - Restriction sites, palindromic sites are restriction enzymes cleave, are found in double-stranded DNA. Palindromic - Restriction sites are palindromic with respect to the complement. These sequences are characterized by inverted repeats in which the 5' to 3' sequence on one strand is identical to the 5' to 3' sequence on the complementary strand.

Answer 39

Plasmids replicate independently of their bacterial chromosome. Therefore, the gene within the plasmid can be amplified to a larger degree than would otherwise be possible.

Answer 40

Steps for generating recombinant DNA are as follows: 1. Synthesize a gene sequence (or “insert”) with the proper restriction sites. 2. Digest the insert and whatever relevant vector components (such as a plasmid) with corresponding restriction enzymes, which cleave at the designed restriction sites. 3. Ligate the vector and the insert together with DNA ligase. 4. Insert plasmid into the bacteria to be replicated. 5. Finally, select for and isolate bacteria containing the plasmid of interest by some means (usually a reporter gene or by treatment with antibiotics).

Answer 41

Engineering plasmids with antibiotic resistance genes enable them to be separated on the basis of antibiotic resistance. When we treat a plate of bacteria with an antibiotic, only those containing the antibiotic resistance gene will survive. Those that contain this antibiotic resistance gene will also contain the gene of interest.

Answer 42

In eukaryotes, RNA polymerase II synthesizes heteronuclear RNA, or hnRNA, which is essentially mRNA.

Answer 43

Transcription is initiated at the promoter on DNA, whereas translation into protein is initiated at the start codon AUG on mRNA

Answer 44

3’-ATCGCTTA-5' The sense, or coding, DNA strand has a sequence identical to that of the RNA transcript, except that thymine is replaced by uracil in RNA. Both the sense strand and the RNA transcript are complementary to the antisense, or template, strand from which the RNA was transcribed. Therefore, the correct sequence is the same as that of the RNA molecule but with T in place of U.

Answer 45

It is catalyzed by polynucleotide adenyltransferase. It provides a binding site for nuclear export proteins. It protects the 3’ end of mRNA from degradation. A longer tail leads to a longer period of stability. The poly(A) tail facilitates binding to nuclear export proteins, which assist with mRNA translocation through pores in the nuclear membrane. The poly(A) tail protects mRNA from degradation in the cytosol as it migrates from the nucleus to ribosomes within the cytosol. 3-prime exonucleases are primarily responsible for dehydration of mRNA in the cytoplasm. The more adenine residues present at the end of the mRNA molecule, the better defense it has against these exonucleases.

Answer 46

Prokaryotes do not have introns or exons and therefore cannot undergo alternative splicing.

Answer 47

During alternative splicing, a complex known as the spliceosome binds to the pre-mRNA and forms a loop. Segments in the loop will be spliced from the mRNA sequence. Here, Segments B (an exon) and C (an intron) will be removed. Contrary to popular misconception, the removal of exons can occur during splicing. In fact, such removal is a primary reason why numerous mRNA transcripts can be generated from a single gene.

Answer 48

Proteins are always synthesized from the amino end (N) of the polypeptide to the carboxylate end (C).

Answer 49

The lac operon is a prokaryotic gene cluster that is under the control of a single promoter and operator: The repressor binds to the operator. RNA polymerase binds to the promoter. Allolactose binds to the repressor to cause it to dissociate. Finally, the CAP protein binds to the CAP binding site.

Answer 50

It involves a repressor and allolactose induces the expression of the structural genes. The lac operon is a prokaryotic operon that includes genes that encode proteins that metabolize lactose. The lac operon is under negative control, as it involves a repressor. The lac operon is inducible as lactose metabolism is induced (turned on) instead of turned off, by certain environmental conditions.

Answer 51

Tryptophan binds the repressor. The repressor binds the operator. The presence of tryptophan blocks the genes for its synthesis.

Answer 52

A mutation in the promoter sequence would prevent initiation of transcription entirely, resulting in a total lack of the relevant protein.

Answer 53

Pre-transcriptional factors include: Methylation (gene silencing), Acetylation (gene activating) and other modifications to DNA. Post-transcriptional factors include: Binding to miRNA MicroRNA is responsible for post-transcriptional silencing. These short, non-coding RNA molecules bind to mRNA, signaling its destruction or promoting degradation of its protective post-transcriptional modifications.

Answer 54

Nearly all cell types within an individual contain the same genome, with some minor differences due to somatic mutation. Rather, it is differential gene expression (from transcription factors, methylation, acetylation, etc) that results in cell morphology and function differences.

Answer 55

Silencers and enhancers are eukaryotic regulatory sequences that are bound by repressors and activators, respectively, to regulate the expression of target genes. RNA polymerase initially binds the promoter sequence before transcribing the target gene.

Answer 56

Messenger RNA (mRNA) is single-stranded RNA transcribed from DNA and is translated by ribosomes into protein. MicroRNA (miRNA) and small interfering RNA (siRNA) are single- and double-stranded RNA sequences, respectively, that target complementary mRNA sequences for destruction, in RNA silencing.

Answer 57

lac operon and trp operon

Answer 58

Uterus While the oocyte will eventually localize to the uterus, this occurs after fertilization in the Fallopian tubes.

Answer 59

An oocyte is an unfertilized female germ cell.

Answer 60

When a **blastocyst** normally implants in the uterine endometrium. Any other location of implantation, such as Fallopian tubes or the cervix, is considered to be an ectopic pregnancy.

Answer 61

Zygote, morulla, blastocyst, gastrula ## Footnote 1. The **zygote** forms after a fertilization event when the sperm and egg nuclei are combined to make one diploid zygote from the two haploid gametes. 2. The zygote undergoes cleavage division as it travels down the Fallopian tubes to the uterus. 3. After the 4th cleavage division, when the zygote is at the 16-cell stage, it is a **morula**. 4. The morula continues to divide and develops a fluid-filled cavity (a blastocoel). The outer cell layer surrounding the blastocoel is the trophoblast. At this point, the morula is now known as the blastocyst. 5. The **blastocyst** implants itself in the uterus, where the trophoblast will differentiate to form the placenta, and an inner cell mass at one pole of the blastocoel will undergo gastrulation: the formation of the 3 primary germ layers (endoderm, mesoderm, and ectoderm). 6. Once gastrulation begins, the blastocyst is a **gastrula**.

Answer 62

Neurulation is the embryonic event where the embryo forms a hollow neural tube from the neural plate: a rod of ectoderm cells forms the notochord (an embryonic midline structure that provides both mechanical and signaling cues to the embryo). Then, the formation of the notochord induces the formation of the neural crest just above it from ectoderm cells.

Answer 63

Vagina, cervix and uterus

Answer 64

The sperm burrows through the corona radiata and latches onto glycoproteins in the zona pellucida. This binding interaction **initiates the acrosomal reaction**. The sperm remains **bound to** the glycoproteins of the **zona pellucida** while it releases digestive enzymes to tunnel through the zona pellucida and permits entry of the sperm nucleus into the egg.

Answer 65

Ectoderm, endoderm, mesoderm

Answer 66

The blastocoel (a fluid-filled cavity in the blastula) forms during blastula development. This is a process that precedes gastrulation, the formation of three germ layers.

Answer 67

Enzymes in the energy payoff phase of glycolysis (in order): G3P dehydrogenase Phosphoglycerate kinase Phosphoglycerate mutase Enolase Pyruvate kinase The energy payoff phase begins with the conversion of G3P into 1,3-bisphosphoglycerate, catalyzed by G3P dehydrogenase. Next, phosphoglycerate kinase converts 1,3-bisphophoglycerate into 3-phosphoglycerate by transferring a phosphate group to generate a molecule of ATP. After that, phosphoglycerate mutase converts 3-phosphoglycerate into 2-phosphoglycerate, which is quickly turned into phosphoenolpyruvate by the enzyme enolase. Lastly, pyruvate kinase converts phosphoenolpyruvate into pyruvate, generating one more ATP.

Answer 68

Molecules that inhibit pyruvate kinase: ATP, Acetyl-CoA and Long chain fatty acids

Answer 69

Both prokaryotes and eukaryotes. Although ethanol fermentation is much more common among prokaryotes than eukaryotes, certain eukaryotes can perform these reactions. The most notable example is yeast, which are single-celled eukaryotes that produce ethanol through ethanol fermentation. They are used to generate fermented food products, like alcoholic beverages.

Answer 70

Yes, the first reaction of ethanol fermentation is a decarboxylation reaction. The enzyme pyruvate decarboxylase cleaves a carbon from pyruvate, releasing it as a molecule of CO2. Oxidation-reduction (redox) reactions involve electron transfer between two species. This description fits the second reaction of ethanol fermentation, in which alcohol dehydrogenase converts acetaldehyde into ethanol. Acetaldehyde gains electrons and gets reduced, while NADH loses electrons and becomes oxidized.

Answer 71

**Pyruvate decarboxylase** and **alcohol dehydrogenase** are associated w/ **Ethanol Fermentation.** **Lactic Acid Fermentation** consists of a single reaction: the conversion of pyruvate to lactic acid by the enzyme **lactate dehydrogenase**. In the process, NADH is oxidized to NAD+.

Answer 72

Replenishing glycogen lost in the liver. Liver cells are responsible for maintaining blood glucose levels within a narrow range. When blood glucose gets too low, they release glucose from storage. However, prolonged fasting and intense exercise deplete the liver’s glucose reserves. Liver cells must make new glucose through gluconeogenesis to replenish their glucose reserves and send glucose molecules out into the bloodstream. Liver cells quickly burn through their glycogen during periods of fasting and physical activity. They must carry out gluconeogenesis to generate glucose and replace the glycogen that was lost.

Answer 73

Substrates that are in glycolysis/gluconeogenesis that are reversible are: Glucose 6-phosphate, Fructose 1,6-bisphosphate and Phosphoenolpyruvate

Answer 74

Gluconeogenic substrates include: Glycine, Alanine, Glycerol and Lactate because they can all be converted into pyruvate.

Answer 75

Liver and kidney. Because liver cells regulate blood glucose levels and store most of the body’s extra glucose, they are also responsible for generating a lot of new glucose molecules through gluconeogenesis. The liver is not the only organ that regulates to blood glucose homeostasis. The kidneys reabsorb glucose from the urine and even create some of their own glucose through gluconeogenesis.

Answer 76

Molecules inhibiting fructose 1,6-bisphosphatase include: AMP and Fructose 2,6-bisphosphate

Answer 77

No, Gluconeogenesis does not occur in all body tissues like Glycolysis does. It is mainly confined to liver and kidney cells, which are in charge of blood glucose homeostasis.

Answer 78

Regulated reactions in gluconeogenesis: Fructose 1,6-bisphosphate + H2O → fructose 6-phosphate Oxaloacetate → phosphoenolpyruvate

Answer 79

ATP and ADP are reactants in glycolysis. ATP is a reactant in two steps of the energy investment phase: the conversion of glucose to glucose 6-phosphate and the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate. ADP is a reactant in two of the later reactions of glycolysis, during the energy payoff phase. In step 7, phosphoglycerate kinase converts 1,3-bisphosphoglycerate into 3-phosphoglycerate, which requires ADP in order to produce ATP. In step 10, the enzyme pyruvate kinase utilizes ADP to produce another molecule of ATP.

Answer 80

Every other reaction than reactions 1, 3 and 10.

Answer 81

The inner mitochondrial membrane is impermeable to almost everything. The only exceptions are water molecules, carbon dioxide, and oxygen.

Answer 82

Yes, mitochondria contain their own ribosomes, which interact with mitochondrial mRNA during mitochondrial protein synthesis

Answer 83

One turn of the citric acid cycle corresponds to the complete oxidation of one molecule of acetyl-CoA, which contains only two carbons. Therefore, we produce: 2 CO2, 1 GTP, 3 NADH and 1 FADH2 during one turn of the cycle

Answer 84

Steps 3, 4, and 10 of the CAC generate NADH. Three NADH are generated in one turn of the citric acid cycle through three key redox reactions all catalyzed by dehydrogenase enzymes. The first is the third step of the cycle, in which isocitrate is converted to alpha-ketoglutarate. In the subsequent step, the conversion of alpha-ketoglutarate to succinyl CoA generates another molecule of NADH. Lastly, NADH is produced in the final step of the citric acid cycle, in which malate is turned into oxaloacetate.

Answer 85

Step 5 Only one citric acid cycle reaction generates GTP, and that is the conversion of succinyl CoA to succinate, which is catalyzed by succinyl CoA synthetase. The high energy thioester bond of succinyl CoA is key to producing high energy GTP.

Answer 86

Step 6 In the next step, succinate dehydrogenase transforms succinate into fumarate, reducing a molecule of FAD to FADH2.

Answer 87

Acetyl-CoA is generated through the oxidative decarboxylation of pyruvate, which is a reaction that releases a molecule of CO2. Coenzyme A is added to the carbon skeleton during this process rather than removed, as this answer choice suggests.

Answer 88

ATP synthase does not function in proton pumping. It uses the proton gradient generated by the other complexes to create ATP.

Answer 89

The following molecules directly inhibit the first step of the Tricarboxylic Acid cycle: ATP, Citrate and Succinyl CoA

Answer 90

The molecules: NAD+ and Coenzyme A upregulate the pyruvate dehydrogenase complex. A high concentration of coenzyme A implies lower concentrations of acetyl-CoA, and therefore an energy deficit inside the cell. Coenzyme A upregulates pyruvate decarboxylation to promote aerobic energy production. NAD+ indicates that the cell needs more energy. When NAD+ builds up to sufficiently high levels, it promotes pyruvate decarboxylation via the PDC, since the aerobic processes that occur downstream of the PDC will convert NAD+ into NADH and allow the cell to generate more ATP.

Answer 91

To the matrix Since the citric acid cycle takes place in the matrix, all citric acid cycle enzymes are found in the mitochondrial matrix

Answer 92

Structural features a mitochondrion has are: A **double lipid bilayer**, Membrane invaginations called **cristae**, Special transport proteins called **porins** that allow ions to move into the mitochondrion (not permeable to protons) and a specialized low pH compartment called the **intermembrane space**

Answer 93

Yes. Oxidative phosphorylation refers to ATP production through the electron transport chain. The **ETC is only located on the inner mitochondrial membrane in eukaryotes.** In **aerobic prokaryotes**, the ETC complexes are embedded into the **inner layer of the plasma membrane** (e.g., the bilayer that faces the cytosol) and protons are pumped into the space between the two lipid bilayers.

Answer 94

Heavily regulated steps of aerobic metabolism are: Alpha-ketoglutarate + NAD+ → succinyl CoA + NADH + CO2. Pyruvate + CoA-SH + NAD+ → acetyl-CoA + CO2 + NADH Acetyl-CoA + Oxaloacetate → citrate + CoA-SH

Answer 95

Secreted signals which act locally on nearby cells and tissue, but do not act systemically through the blood, are paracrine signals. Juxtacrine signaling occurs when two cells are adjacent to one another and are connected by physical signals.

Answer 96

A traditional ligand-gated ion channel is activated when a signaling molecule from outside the cell binds to it. Signaling molecule 1 is a first messenger (a ligand that activates a receptor to produce intracellular signaling). Signaling molecule 2 should be the canonically accepted "second messenger" like Calcium or cAMP which can act in many ways depending on the context of the cell in which it is taken up.

Answer 97

Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. An RTK works through a multi-step process. First, the receptor’s active site binds to its ligand, leading to receptor dimerization, leading to RTK auto-phosphorylation, leading to substrate phosphorylation, and, finally, leading to downstream effector action.

Answer 98

Upon GPCR activation, an associated G-alpha protein swaps GDP for GTP and then activates further signaling molecules downstream. The G-alpha protein is a GTPase, an enzyme that hydrolyzes GTP to GDP by the addition of a water molecule. The G-alpha protein is only “inactivated” when it hydrolyzes GTP back to GDP. Therefore, if the GTPase activity was inhibited, the G-alpha protein would be permanently “on”. The effects of the GPCR would be constitutively active.

Answer 99

Seven hydrophobic regions; activates a trimeric GTPase; activates a signaling pathway specific to the GPCR | A GPCR has seven transmembrane passes through the hydrophobic cell membrane. A GPCR, once activated, activates a heterotrimer, inducing a G-alpha protein to swap GDP for GTP. The G-alpha protein then activates a downstream pathway specific to the GPCR in question – either the cAMP or IP3 second messenger pathways.

Answer 100

SDS (Sodium Dodecyl Sulfate) is an amphipathic detergent, containing both polar and nonpolar regions, that disrupts hydrophobic interactions in a protein, which results in disrupted protein folding.

Answer 101

Quaternary, Tertiary and Secondary protein structures are reversible. Certain denaturation methods are irreversible (like heat denaturation during cooking!)

Answer 102

Right-shift Decreased affinity for O2, increased partial CO2 pressure, increased pH, increased 2,3-BPG and increased temperature Left-shift Increased affinity for O2, decreased partial CO2 pressure, decreased pH, decreased 2,3-BPG and decreased temperature and increased Fetal Hemoglobin affinity for O2

Answer 103

Fetal hemoglobin has a lower affinity for 2,3-BPG because it must must draw its oxygen from maternal hemoglobin, which necessitates a slightly higher oxygen affinity. This is accomplished, in part, by a reduction in the binding of 2,3-BPG. Since 2,3-BPG normally decreases oxygen affinity, a reduction in the binding of this compound ultimately increases fetal hemoglobin’s affinity for oxygen. Cooperativity is unaffected because the same principles of oxygen delivery apply to the fetus as to the adult.

Answer 104

2,3-BPG reduces the affinity of hemoglobin for oxygen, which facilitates more effective oxygen delivery to the tissues. This corresponds to a rightward shift in the dissociation curve. In the presence of this compound, at a given partial pressure of oxygen, a comparatively low percentage of hemoglobin will be saturated with oxygen.

Answer 105

The T-state is the deoxy form of hemoglobin (meaning that it lacks an oxygen species) and is also known as "deoxyhemoglobin”. The R-state is the fully oxygenated form: "oxyhemoglobin." In the sequential mode of cooperativity (Koshland's hypothesis), the conformation state of the monomer changes as it binds to oxygen.

Answer 106

Red blood cells contain hemoglobin, contain glycoproteins on the cell surface, are destroyed in the spleen and do not contain a nucleus.

Answer 107

Systemic circulation starts when the left ventricle contracts. The blood travels through the aorta, follows by the arteries and arterioles, and arrives at the capillaries where gas and waste exchange occurs. The blood then enters the venous system and first encounters venules, followed by veins, and finally the vena cava.

Answer 108

Atherosclerosis is the build up of fatty deposits in the arterial circulatory system, most commonly the coronary arteries. The circulatory system consists of three independent systems that work together: the heart (cardiovascular), lungs (pulmonary), and arteries, veins, coronary and portal vessels (systemic). The system is responsible for the flow of blood, nutrients, oxygen and other gases, and as well as hormones to and from cells.

Answer 109

The SA node fires and sends the signal to the atria to fully contract. It also propagates a signal to the AV node, which then relays this signal to the bundle of His, and that signal then is passed through Purkinje fibers. The spreading of the impulse from the AV node is what triggers the ventricles to contract. SA node -\> Atria -\> AV node -\> Bundle of His -\> Purkinje fibers

Answer 110

The T-state is the deoxy form of hemoglobin (meaning that it lacks an oxygen species) and is also known as "deoxyhemoglobin”. The R-state is the fully oxygenated form: "oxyhemoglobin." In the sequential mode of cooperativity (Koshland's hypothesis), the conformation state of the monomer changes as it binds to oxygen.

Answer 111

Cells can be mutated by radical species, the presence of high-energy emission radioisotopes, or exposed to ultraviolet light, which both dimerizes adjacent pyrimidines and radicalizes oxygen molecules.

Answer 112

Mutagen-induced DNA mutations are not negative side effects of aging. Mutagen-induced are generally environmental agents that can damage our DNA and induce mutations. For example, exposing a person to UV light will induce DNA mutations. However, there is no reason to believe that a person is exposed to more mutagens as they age. Spontaneous DNA Mutations are mutations that result from natural biological processes such as errors in DNA repair. Spontaneous mutations increase as we age, because errors in processes such as DNA repair increase as we age.

Answer 113

A gain-of-function mutation is any mutation which causes a protein to have new or enhanced functionality. The definition of a loss-of-function mutation is any mutation which causes a protein to have reduced functionality.

Answer 114

A spermatogonium is the diploid precursor to haploid spermatids. In other words, spermatagonia undergo meiotic divisions to form haploid gametes, eventually divvying up their genetic material between 4 daughter gametes. If a translocation occurs in a spermatogonium and one chromosome ends up with one extra gene copy, while another chromosome ends up with one less, the resultant daughter gametes could eventually produce offspring with extra or fewer copies of genetic material. Offspring with extra or fewer copies of genes on their chromosomes may have altered gene expression, producing more or less mRNA, respectively.

Answer 115

Transposons are generally non-coding sequences of DNA which, through enzymatic action, can jump from location to location within the genome. When this jumping activity occurs from one chromosome to another, the resulting transposition is simply transposon genetic material being added to another chromsome with no other genetic material being exchanged. Thus, **transposition** can be described as **unidirectional**.

Answer 116

Mismatch repair activity ONLY repairs mutations caused by errors in replication whereas DNA repair processes (other than mismatch repair) will repair nonspontaneous mutations due to the action of mutagenic agents, such as UV light or free radicals.

Answer 117

Base excision repair processes are likely to occur after a mutagenic compound has been aded to a cell. Peroxide is a reactive oxygen species, a class of chemicals which contains oxygen and generates highly reactive free radicals. As such, peroxide is likely to damage DNA and one could reasonably predict that it induced base excision repair.

Answer 118

Base mismatch errors during transcription would lead to an incorrect mRNA transcript. A strand of mRNA exists only transiently, coding for its respective protein, before degrading. Unnoticed base mismatching during replication will cause permanent changes to the genetic code in a cell, irreversibily altering a cell's DNA.

Answer 119

The conversion of leucine to aspartic acid, without disrupting the protein's reading frame, requires 3 point mutations. UV light nonspecifically damages DNA by inducing pyrimidine dimerization, which is not the same kind of mutation as a missense mutation.

Answer 120

A mutagen is any physical or chemical agent from inside OR outside the body which increases the observed frequency of DNA Mutations.

Answer 121

Yes. Relative transcription of genes is limited by the number of copies of each gene. Aneuploidy is an abnormal number of chromosomes, an example of which is monosomy, or the deletion of an entire chromosome. Chromosomal deletions result in the loss of regions of genetic material along a chromosome. Therefore, both are likely to reduce gene copy number and reduce gene expressivity.

Answer 122

Steps of Action Potential (in order) 1) Neurotransmitter binds to dendritic receptor 2) Influx of specific ion 3) Generation of graded potential 4) Spatial or temporal summation

Answer 123

The superior colliculus is a paired structure consisting of two superior colluculi involved in the processing of visual information and production of visual reflexes.

Answer 124

The cerebellum is primarily involved in the smoothing and fine-tuning of motor movements and posture.

Answer 125

Both Broca’s area and Wernicke’s area are localized to the left, and not right, hemisphere of the brain. Broca’s area is localized to the left side of the frontal lobe, whereas Wernicke’s area is localized to the left side of the temporal lobe. Broca’s area is involved in speech production and Wernicke’s area is involved in language comprehension.

Answer 126

The hormone ACTH is produced by the anterior pituitary.

Answer 127

Endocrine gland regulator and Tropic hormone

Answer 128

Frontal lobe - higher level cognition Parietal lobe - sensory processing Temporal lobe - primary visual cortex Occipital lobe - language processing and memory

Answer 129

Pons, Midbrain and Medulla Oblongata

Answer 130

Autonomics Ganglia are intermediate junctions between the central nervous system and target organs. Autonomic ganglia serve as intermediates for the neural impulse of the central nervous system.

Answer 131

Somatosensation is processed at the primary somatosensory cortex, located on the postcentral gyrus in the parietal lobe.

Answer 132

The visual pathway passes through the superior colliculus and the lateral geniculate body of the thalamus before arriving at the occipital lobe.

Answer 133

The auditory pathway passess through the similar named medial geniculate body and inferior colliculus, before being processed in the temporal lobe.

Answer 134

Astrocytes transport nutrients, such as glucose, and contribute to forming the blood brain barrier.

Answer 135

Ependymal cells secrete and circulate cerebrospinal fluid, which lubricates and protects the central nervous system.

Answer 136

**Graded potentials** can refer to both excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). Enough graded potentials must accumulate to push the membrane potential past a certain depolarization threshold in order to generate an action potential. However, not all graded potentials cause depolarization. EPSPs cause depolarization and will help push the membrane potential towards the threshold, but IPSPs cause hyperpolarization and will push the membrane potential farther away from the threshold.

Answer 137

The inner ear contains the semicircular canals, which are responsible for sensing rotational acceleration and it contains the vestibule, which is responsible for sensing linear acceleration.

Answer 138

Photoreceptors, horizontal cells, bipolar cells, amacrine cells and ganglion cells

Answer 139

**Sound waves cause the hair cells to move around in the endolymph**, and that **swaying movement of the stereocilia** opens up ion channels that let small **positively-charged ions flow into the cell**. This, in turn, triggers an influx of calcium ions through voltage-gated calcium channels. This **Ca2+ influx** then causes the **release of neurotransmitters** at the other end of the cell, beginning the transmission of neural signals. These **signals are transmitted through the vestibulocochlear nerve,** which is also sometimes referred to as the auditory nerve. **Auditory signals are passed through several different structures in the brain, including the medial geniculate nucleus in the thalamus**. Finally, these **signals are processed by the auditory cortex** in the temporal lobe.

Answer 140

The organ of Corti is divided into several layers, with a flexible structure called the basilar membrane on the bottom, hair cells suspended in endolymph in the middle, and a more rigid structure known as the tectorial membrane on top.

Answer 141

The basic job of the vestibule is to sense linear acceleration. In turn, it contains two sub-structures: the utricle, which detects motion in the horizontal plane, and the saccule, which detects motion in the vertical plane. These structures contain tiny little calcium carbonate (CaCO3) specks called otoliths, which help stimulate the hair cells.

Answer 142

Information about taste is first processed in the taste center of the thalamus, and then sent to the gustatory cortex. Smells are first processed in the olfactory bulb in the front of the brain and are then passed along to the olfactory tract. After information on smells is processed by the olfactory tract, it is processed by other parts of the brain, including the limbic system, which is involved in emotion. This helps explain why certain smells can be powerfully evocative of certain places, people, and times in our lives.

Answer 143

The most abundant leukocytes are neutrophils, which make up about 60% of all leukocytes. After neutrophils, the next most abundant class of white blood cells are lymphocytes, which account for about 30% of white blood cells. Monocytes make up about 5% of the leukocytes.

Answer 144

Yes, in a healthy person

Answer 145

Macrophages and Dendritic Cells

Answer 146

Macrophages can be thought of as the all-purpose garbage trucks of the immune system. They phagocytose almost anything, including tumor cells, foreign substances, microbes, and cellular debris. They are found in almost all body tissues and constantly on patrol for things that need to be destroyed.

Answer 147

The lymphatic system contains hundreds, not thousands, of lymph nodes.

Answer 148

No, Anaphylaxis is a severe systemic reaction that can lead to swelling in the throat and difficulty breathing following exposure to an allergen. In autoimmunity, there is a different type of T-cell involved than in allergies. In an autoimmune response, tissue destruction occurs.

Answer 149

Host tissue is the target of the immune system with autoimmune diseases.

Answer 150

Because of bone marrow’s essential function in leukocyte synthesis, diseases that attack the marrow, such as leukemia or other cancers of the blood, compromise the immune system and increase the risk of infection.

Answer 151

No autoimmune reaction is happening. This suggests that the patient’s own immune cells are not displaying a reaction to the cells of the thyroid which provides evidence against autoimmunity.

Answer 152

The renal corpuscle is an element of the nephron. It functions in blood filtration. It is directly connected to the renal tubule.

Answer 153

It is a component of the renal corpuscle. It is located inside Bowman’s capsule. Hydrostatic pressure within the glomerulus promotes solute filtration.

Answer 154

The PCT facilitates reabsorption of metabolically useful solutes such as glucose, amino acids, vitamins, and certain ions. During reabsorption, these molecules are removed from the filtrate within the renal tubule and reintroduced into the bloodstream.

Answer 155

The Descending Loop of Henle is in close contact with blood vessels called vasa recta. It concentrates filtrate passing through the renal tubule. It utilizes the osmotic gradient established by the ascending limb.

Answer 156

Water is reabsorbed in the collecting duct, which reduces filtrate volume and ultimately increases its osmolarity.

Answer 157

Vasopressin, also called antidiuretic hormone (ADH), stimulates water reabsorption in the collecting duct. Aldosterone promotes sodium ion reabsorption within the distal convoluted tubule and in the collecting duct. Parathyroid hormone acts on cells of the distal convoluted tubules to increase calcium ion reabsorption.

Answer 158

Protons will be secreted into the renal tubule to increase plasma pH.

Answer 159

Reabsorption within the renal tubule refers to the reuptake of metabolically valuable small molecules that were filtered out of the bloodstream in the renal corpuscle. These ions, vitamins, and nutrients pass out of the renal tubule and into the surrounding peritubular capillaries to reenter the bloodstream.

Answer 160

Blood pressure, Blood osmolarity, pH balance and Nitrogenous wastes

Answer 161

Vasopression (ADH) and aldosterone Vasopressin, also known as antidiuretic hormone (ADH), increases blood pressure by increasing water reabsorption in the collecting duct. It promotes the insertion of water channels called aquaporins into the membranes of collecting duct cells, which allows water to flow back into the bloodstream along its osmotic gradient. Aldosterone increases blood pressure indirectly. It increases sodium uptake in the distal convoluted tubule and collecting duct, which, in the presence of ADH, promotes water reabsorption.

Answer 162

Increased sodium levels and high blood pressure Renin is released by the juxtaglomerular cells of the kidneys in response to low blood pressure and/or low plasma sodium. It acts within the renin-angiotensin-aldosterone axis, which ultimately results in aldosterone production. Aldosterone increases sodium reabsorption in the distal convoluted tubule and collecting duct of the nephron. In the presence of ADH, this promotes water reabsorption. Therefore, renin overexpression would cause water retention, which would result in high blood pressure. Because renin promotes aldosterone release, and aldosterone increases sodium reabsorption in the nephron, this patient would likely have too much sodium in his or her bloodstream.

Answer 163

In the **collecting duct**, large amounts of water can be reabsorbed due to the action of **vasopressin (ADH)**, which promotes the expression of aquaporins on the membranes of collecting duct cells. Water reabsorption significantly increases filtrate osmolarity, and it is transformed into urine.

Answer 164

In the proximal convoluted tubule, water, ions and metabolically valuable molecules are reabsorbed (such as vitamins, amino acids, and glucose) and waste products are secreted.

Answer 165

The physical or chemical barriers used by the innate immune system are: mucous, skin and lysozymes.

Answer 166

Typical immunoglobulins contain 4 protein subunits: 2 light chains and 2 heavy chains.

Answer 167

T cells only mobilize an immune response if the MHC-I antigen complexes are abnormal. Viral or Tumor.

Answer 168

Plasma and memory B cells are components of the humoral adaptive immune system, which involves the release of antibodies into the bloodstream.

Answer 169

Dendritic cells are a class of antigen presenting cells that help activate T cells.

Answer 170

Lymphocytes include both T and B cells, which drive the acquired (adaptive) immune system.

Answer 171

For the antibody titer, the synthetic varicella antigen is immobilized on a solid surface and the patient’s blood sample is added. If the patient has no previous exposure to varicella, the patient will have no antibodies specific to varicella in his blood. The test result will be negative, and the doctor would vaccinate the patient.

Answer 172

Intermediate filaments are composed of multiple protein types.

Answer 173

Replacement of ADP with ATP causes a conformational shift that propels the kinesin forward. Kinesin movement begins with ATP binding to the lead head group. This binding promotes a conformational change that swings the tailing head group toward the + end of the microtubles, thus propelling kinesin forward.

Answer 174

Dynein helps with moving **organelles** and **phospholipids** more interior within the cell. Long Explanation: Both kinesins and dyneins can transport phospholipids. The motor protein used depends on where the phospholipid is headed. If it’s bound for the plasma membrane, a kinesin would carry out its transport. If the phospholipid is intended for a vesicle or membrane-bound organelle that is closer to the center of the cell relative to where it is synthesized, then a dynein will take the job. Moving organelles from peripheral locations to more central regions and help position them stably within the cytoplasm. Specific Examples: Transport of newly synthesized phospholipids. Cytoplasmic positioning of the Golgi apparatus.

Answer 175

The key difference between kinesins and dyneins is the direction of movement.

Answer 176

Gap junctions are created by connexin proteins, which create small pores between cells to allow the exchange of solutes between them.

Answer 177

In response to an infection, specialized immune cells release cytokines, which promote selectin production in epithelial cells near the infected site. Selectins protrude from the plasma membrane, trapping leukocytes moving through blood vessels to divert them toward the infected site.

Answer 178

Cadherins help connect cells to other cells through adherens junctions and desmosomes.

Answer 179

Integrins bind cells to their extracellular matrix by connecting cytoskeletal filaments inside the cell to matrix proteins outside the cell.

Answer 180

Antibodies are: Antibodies are glycoproteins. Antibodies are part of the humoral immune response. Antibody isotypes are differentiated by the constant domain of their heavy chains. Antibody specificity is achieved through random mutations.

Answer 181

Normal functions of antibodies include: **pathogen identification** and **neutralization of viruses.**

Answer 182

Keratin is a polymer of alpha helical proteins. Intermediate filaments like keratin are created from various protein subunits that contain alpha helical sections, which look a bit like corkscrews. These domains allow monomers to curl around each to form bundles.

Answer 183

IgA is found in mucous membranes of the gut, respiratory tract, and genital tract. It is specialized to fight pathogens on the front lines, so to speak, and has special features that protect it from proteolytic enzymes and microbes found in mucous membranes.

Answer 184

IgD is expressed on the surface of naïve B cells, which are B cells that have not yet been exposed to an antigen. When an IgD binds to an antigen, it helps activate its B cell.

Answer 185

IgE mediates allergic and parasitic responses in infected and inflamed tissue. When an IgE antibody encounters its antigen, it stimulates immune cells to release histamine, which dilates capillaries and helps recruit other immune cells to the area.

Answer 186

G-actin units polymerize end-to-end in the cytosol to form the polymer F-actin. A single microfilament typically consists of two F-actin strands. Actin polymerization takes place in the cytosol. G-actin subunits polymerize in a linear fashion, with one subunit adding sequentially to the next. Microfilaments usually contain two strands of F-actin that wrap around each other horizontally.

Answer 187

Each heavy chain contains three different domains: the constant domain, variable domain, and hypervariable domain. The constant domain is the same for antibodies of the same class, whereas the variable and hypervariable regions can be slightly to significantly different.

Answer 188

Tight junctions are extremely close linkages between two cells and prevent solute diffusion. However, they are **not composed of cadherin**. There are **roughly 40 specialized proteins** that come together to create a tight junction.

Answer 189

You can think of adherens junctions as “all purpose” anchoring junctions, since they are very common in most tissues. Desmosomes are a bit more specific because they interact with the cell’s intermediate filaments rather than actin filaments. As a result, they are a bit stronger than adherens junctions and tend to be most common in cells that have to withstand a lot of force, like cardiac muscle and bladder cells.

Answer 190

The concentration of actin or tubulin subunits in different areas of the cell regulate microfilament and microtubule dynamics.

Answer 191

All carbohydrates (except for certain notable exceptions such as deoxysugars) share the **same** **empirical formula**, Cm(H2O)n, where m is the number of carbons and n is the number of molecules of water. Starch is a polysaccharide and glucose (shown) is a monosaccharide, meaning that both share this formula.

Answer 192

Ribose is a five carbon aldose, otherwise known as an aldopentose. D-Ribose is an easy and useful structure to memorize and be able to recognize on the MCAT, because all of its hydroxyl groups point to the right.

Answer 193

Galactose and glucose monomers can be linked to form the disaccharide lactose. The beta-glycosidic bond between the two monomers is created between the 1 position carbon of galactose, and the 4 position of glucose.

Answer 194

Human skeletal muscle does store glycogen and break it down during activity, but it uses the resultant glucose itself. Secondly, the liver is the primary storage site of glycogen polymers which results in increased blood glucose after breakdown.

Answer 195

Glycogen contains many **more alpha-1,6** bonds than amylopectin. This gives glycogen a greater degree of branching than amylopectin, allowing it to better serve its purpose as a storage molecule.

Answer 196

Peptidoglycan composes the cell wall outside of the cell membrane of bacteria, not the cell membrane itself.

Answer 197

Ketohexose. Fructose has a ketone group, and is therefore a ketose. It also has six carbons, and is thus a hexose.

Answer 198

The anomeric carbon, carbon-1 (bearing an aldehyde group in its straight chain form), can be attacked by a hydroxyl group in order to form a ring structure. In the ring form of D-glucose, carbon-1 will participate in glycosidic linkages to other sugars.

Answer 199

The anomeric carbon of a monosaccharide is the **carbon** at which a **carbonyl functional group is located**. On some sugars, such as aldoses like glucose, this is at the C-1 position. On other sugars, such as ketoses like fructose, this is at the C-2 position.

Answer 200

Glycogen - Alpha-1,4 bonds with a high frequency of alpha-1,6 branches Amylopectin - Alpha-1,4 bonds with a low frequency of alpha-1,6 branches Amylose - Beta-1,4 bonds Cellulose - Alpha-1,4 bonds Both glycogen and amylopectin contain alpha-1,4 bonds between each and every glucose monomer in their chain. However, glycogen contains many more alpha-1,6 bonds than amylopectin. This gives glycogen a greater degree of branching than amylopectin, allowing it to better serve its purpose as a storage molecule. Amylopectin and amylose are the two polymers making up starch. Amylose is long chains of glucose connected by alpha-1,4 bonds. Cellulose is a carbohydrate polymer found in plants, made up of beta-1,4 bonds.

Answer 201

Muscle, Muscle Bundle, Fascicle, Muscle Fiber, Myofibril, Sarcomere

Answer 202

Acetylcholine binds the postsynaptic receptor Influx of sodium ions from the extracellular environment Release of calcium from the sarcoplasmic reticulum Conformational change of tropomyosin Binding of myosin to Actin

Answer 203

Once ATP is bound to the myosin head it can be hydrolyzed (by myosin), moving it in the cocked position. Once this occurs, calcium ions bind to troponin within the tropomyosin complex, revealing the myosin binding sites on actin. Bound myosin then releases the inorganic phosphate, initiating the power stroke. The myosin stays bound to the actin filament until a new ATP molecule binds to it, releasing it from actin.

Answer 204

The time it takes for one contraction/relaxation cycle to occur in a muscle fiber.

Answer 205

Prolonged muscle contractions due to hyperstimulation of the nicotinic acetylcholine receptors.

Answer 206

**Hair** are composed of **epithelial cells** being pushed outward by a dividing lower layer, and as they get further from the nutrient supply, they die and are keratinized. The **follicle** itself, however, is located physically in the **dermis**, where it is protected from bacterial infections.

Answer 207

Striated muscle carries out Thermoregulation, Movement, Circulation and Digestion

Answer 208

Skeletal myoctes are the only type of myocyte that is multinucleate. Cardiomyocyte and Smooth Myocyte are uninucleate.

Answer 209

Binding of calcium ions to troponin is regulated by intracellular levels of calcium, which is in turn regulated by action potentials initiated by acetylcholine binding its receptor on the myocytes surface.

Answer 210

Functions of skin include: **Waste Excretion**, **Thermoregulation**, **Protection** and **Sensation**

Answer 211

Glands in the mouth produce saliva, which contains an enzyme that kills bacteria. Saliva contains lysozyme, which catalyzes the destruction of bacterial cell walls.

Answer 212

Villi are finger-like projections of the small intestine’s epithelial surface, and each villus contains many enterocytes. Each enterocyte contains many microvilli. Enterocytes are the epithelial cells that make up the small intestine. Because villi are tiny folds of the small intestine’s epithelial surface, each villus is composed of hundreds of enterocytes. Microvilli are microscopic hair-like extensions of each enterocyte’s cell membrane.

Answer 213

Fatty acids, Amino acids and Monosaccharides Disaccharides get broken up into Monosaccharides before entering the small intestine. Enterocytes secrete enzymes called disaccharidases that cleave disaccharides, generating monosaccharides, which are much easier to absorb.

Answer 214

CCK stimulates the release of bile from the gallbladder and digestive enzymes from the pancreas. Secretin is a hormone that stimulates the release of Bicarbonate which neutralizes chyme entering the duodenum.

Answer 215

Secondary active transport couples the movement of an ion down its concentration gradient with the movement of a solute against its gradient. First, a sodium-potassium pump uses energy to generate an electrochemical gradient that maintains a low sodium concentration inside the cell. Although this “active transport” step does not directly involve glucose, it is a key preparatory step for glucose transport. Because the concentration of sodium is much higher outside of the cell, it easily flows back into the cell through a sodium-glucose symporter protein.

Answer 216

Salivary amylase generates disaccharides. Pepsin generates peptides. Lingual lipase generates fatty acids. Disaccharides generate monosaccharides. Pancreatic proteases generate amino acids.

Answer 217

Fatty acids do not immediately enter circulation after absorption. After they are absorbed by enterocytes, they are packaged into chylomicrons and shunted into lacteals. Lacteals are small lymphatic vessels that drain into larger lymphatic vessels, which eventually empty into the bloodstream.

Answer 218

Because **fatty acids** are small and hydrophobic, they can **diffuse** directly through the plasma membranes of enterocytes. Some **monosaccharides** are absorbed via **secondary active transport** and others through **facilitated diffusion**. Sugars cannot passively diffuse through cell membranes. Like monosaccharides, **amino acids** are absorbed via **secondary active transport** rather than passive diffusion.

Answer 219

The only major macromolecule that is digested in the stomach is protein. Chief cells in the stomach secrete a proenzyme called pepsinogen, which is cleaved by gastric acid, forming active pepsin. Pepsin breaks down proteins into smaller fragments called peptides.

Answer 220

The liver receives blood-borne compounds via the hepatic portal system, synthesizes and secretes bile and metabolizes pharmaceutical agents.

Answer 221

Insulin-responsive cells in response have the secretory vesicles containing GLUT4 transporters in their membranes fuse with the cell plasma membrane. GLUT4 transporters are stationed in the membrane of secretory vesicles waiting for their signal, and in response to insulin, these vesicles fuse with the plasma membrane, allowing glucose to move into the cell from the bloodstream.

Answer 222

Glucose is brought into the cell via facilitated diffusion through GLUT4 transport channels. Facilitated diffusion differs from simple diffusion in that some sort of transport channel is used whereas simple diffusion is completely unassisted transport across a membrane.

Answer 223

Type 1 diabetes is associated with an autoimmune disease. Types 1 and 2 are associated with mutated, non-functioning insulin. Type 2 is associated with insulin resistance. Both type 1 and type 2 diabetes manifest through high blood glucose levels, and are associated with insulin dysfunction. Type 1 diabetes is an autoimmune condition in which the body’s own immune system attacks and destroys the pancreatic beta cells responsible for producing insulin. Type 2 diabetes instead involves insulin resistance. Neither type of diabetes involves defects of the insulin molecule itself.

Answer 224

Glucagon is a **peptide hormone composed** of **amino acids**. Glucagon is **synthesized** by special cells in the pancreas known as pancreatic **alpha cells**. Glucagon is secreted when there is too little glucose in the blood. On a technical level, it actually **responds** to **low insulin concentrations** in the blood, which tell the alpha cells that blood glucose is low. Not surprisingly, then, high insulin concentrations inhibit glucagon production and release.

Answer 225

1. Activation of PKA 2. Activation of Hormone-Sensitive Lipases 3. Lipases Hydrolyze Triglycerides 4. Free Fatty Acids Released into the Bloodstream Activation of PKA, hormone-sensitive lipases activated, lipases hydrolyze triglycerides, and, finally, free fatty acids released into the bloodstream. Glucagon activates protein kinase A, which then activates hormone-sensitive lipases in adipose tissue. These lipases, in turn, hydrolyze triglycerides to release free fatty acids and glycerol into the bloodstream.

Answer 226

- high intracellular ATP concentration - potassium buildup that creates a drop in the cell membrane potential - high intracellular calcium concentration

Answer 227

About 30 minutes after eating, your glucose concentrations will be high. High blood glucose concentrations stimulate insulin release from beta pancreatic cells, so insulin levels should also be high. Insulin inhibits glucagon production and release so we would expect glucagon levels to be very low. Insulin also promotes anabolic processes centered around uptake of excess glucose from the bloodstream and converting it to glycogen or triglycerides for energy storage to be used later in a time of need.

Answer 228

Compounds classified as lipids are prostaglandins and terpenes. Prostaglandins are a subclass of eicosanoids, which are a broad family of signaling lipids involved in many key physiological processes. Prostaglandins mediate inflammatory pathways. Terpenes are a special class of lipids that are made from isoprene, which is a 5-carbon branched structure with two unsaturations.

Answer 229

Waxes consist of a mixture of fatty acid esters formed from long chain alcohols, aromatic compounds, and other diverse functional groups. The easiest way to recognize the structure above as a wax is through process of elimination. It is clearly a fatty acid derivative but does not have the correct functional groups to qualify as a phospholipid, sphingolipid, or triglyceride.

Answer 230

Sphingolipids are signaling lipids derived from sphingosine, which is an amine alcohol group. The sphingolipid depicted is a ceramide: the simplest class of sphingolipids.

Answer 231

**D vitamins** are lipid-soluble vitamins derived from cholesterol. In biological systems, UV light lyses one of cholesterol’s 4 fused rings to produce one of several precursor molecules for the five D vitamins.

Answer 232

Although **waxes** do contain many diverse functional groups, they are not cholesterol derivatives. Instead, they are **derived** from **long chain fatty acids**.

Answer 233

The molecules that are found in a triacylglycerol are fatty acid(s) and a glycerol backbone. Triglycerides are esters composed of **three fatty acids** connected to a molecule of **glycerol**.

Answer 234

Omega notation is unusual in that it counts carbons from the non-carbonyl end of the fatty acid. Omega-3 fatty acids always contain a double bond between C3 and C4 from the non-carbonyl end.

Answer 235

A newly synthesized chylomicron would start in the intestinal epithelium, followed by lacteals, followed by lymphatic vessels, followed by adipose tissue, followed by liver tissue. After a meal, dietary lipids are absorbed by epithelial cells on the brush border of the small intestine. Inside these cells, they are packaged into chylomicrons, which contain amphipathic apolipoproteins and are rich in trigylcerides. Fully formed chylomicrons enter lacteals, which are small vessels that drain into the lymphatic system. From the lymphatic system, they enter various body tissues, including adipose tissue, to deliver fatty acids. Once stripped of most of their cargo, chylomicrons are scavenged by other lipoproteins and returned to the liver, where their remains can be recycled.