AAMC 2 - Bio/Biochem

Question 1

Do purines have a two-ring structure?

Answer 1

Yes.

Purines (like adenine & guanine) contain a fused two-ring structure.

Question 2

Do pyrimidines have a two-ring structure?

Answer 2

No.

Pyrimidines (like thymine and cytosine) are made of a single ring structure.

Question 3

Describe the structure or purines and pyrimidines, respectively.

Answer 3

Purines: Composed of a fused two-ring structure. Examples include Adenine and Guanine.

Pyrimidines: Composed of a single ring structure. Examples include Thymine and Cytosine.

Question 4

What is the only amino acid containing a sulfhydryl group?

Answer 4

Cysteine is the only amino acid that contains a sulfhydryl group (thiol and sulfonyl are alternative names).

Note: methionine contains a sulfur but it is NOT an -SH group. It is a sulfur bond by two carbons.

Question 5

A large carbohydrate is tagged with a fluorescent marker and placed in the extracellular environment around a macrophage. The macrophage ingests the carbohydrate via phagocytosis. Which cellular structure is most likely to be fluorescently labeled upon viewing with a light microscope soon after phagocytosis? Explain the process used by the structure you choose.

A. Nucleus

B. Golgi apparatus

C. Lysosome

D. Endoplasmic reticulum

Answer 5

C. Lysosome

The answer to this question is C because:

1. when a macrophage ingests foreign material, the material initially becomes trapped in a phagosome.
2. The phagosome then fuses with a lysosome to form a phagolysosome.
3. Inside the phagolysosome, enzymes digest the foreign object.

Of the cell structures listed, the labeled carbohydrate is most likely to be microscopically visualized within a lysosome (phagolysosome).

Question 6

Inhibition of phosphofructokinase-1 by ATP is an example of:

I. allosteric regulation.

II. feedback inhibition.

III. competitive inhibition.

A. I only

B. III only

C. I and II only

D. II and III only

Answer 6

C. I and II only

The answer to this question is C because ATP, the end product of glycolysis, downregulates through feedback inhibition the activity of phosphofructokinase-1 by binding to a regulatory site other than the active site of the enzyme (allosteric regulation). In contrast, competitive inhibition involves competition for binding to the active site.

Question 7

Can an allosteric regulation be classified as competitive inhibition at the same time?

Answer 7

No.

By definition, allosteric regulation is inhibition by binding somewhere other than the active site.

Question 8

What do you know about a protein or molecule if the isoelectric point is 9?

Answer 8

A molecule with an isoelectric point of 9 will be positively charged at physiological pH

Question 9

Does folding into tertiary structure occur in the cytoplasm?

Answer 9

No.

Although the hydrophobic effect is greatly associated with protein folding, we know that proteins are folded in the rough endoplasmic reticulum.

Question 10

Where are secretory proteins synthesized?

Answer 10

In the rough endoplasmic reticulum

Question 11

β-catenin (a protein that activates transcription factors for certain genes) most likely has:

A. multiple subunits.

B. very few disulfide bonds.

C. a nuclear localization sequence.

D. a high proportion of surface-exposed nonpolar residues.

Answer 11

C. a nuclear localization sequence.

β-catenin activates transcription factors for target genes. As transcription factors are found in the nucleus, β-catenin must enter the nucleus.

Proteins that are translocated into the nucleus usually contain a nuclear localization sequence.

Question 12

What is ubiquitination?

Answer 12

Ubiquitination targets a protein for degradation by a proteasome.

Question 13

Under what condition will disulfide bonds be broken?

Answer 13

Disulfide bonds will be broken under reducing conditions (low pH)

Question 14

Under what conditions will disulfide bonds be formed between cysteine residues?

Answer 14

Cysteine residues will form disulfide bonds under oxidizing conditions (high pH)

Question 15

The enzyme encoded by the tdh2 gene (glyceraldehyde-3-phosphate dehydrogenase (GAPDH)) catalyzes the reversible conversion of:

A. 3-phosphoglycerate to 1,3-bisphosphoglycerate.

B. glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.

C. fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate.

D. 2-phosphoglycerate to 3-phosphoglycerate.

Answer 15

B. glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.

This is step 5 of glycolysis.

Question 16

What is the best experimental method to analyze the effect of tdh2 gene deletion on the rate of histone acetylation? Comparing histone acetylation in wild-type and Δtdh2 cells by:

A. Western blot

B. Southern blot

C. Northern blot

D. RT-PCR

Answer 16

A. Western blot

Posttranslational modification of proteins such as histone acetylation is analyzed by Western blotting.

Question 17

Posttranslational modification of proteins such as histone acetylation is analyzed by ______ blotting.

Answer 17

Posttranslational modification of proteins such as histone acetylation is analyzed by Western blotting.

Question 18

Histone acetylation and methylation are examples of what kind of modification?

Answer 18

Posttranslational modification.

These can be analyzed using western blotting.

Question 19

How can a researcher analyze a sample to see if post-translation modifications have occurred?

Answer 19

Western Blotting

Question 20

What are the primary myelin-forming cells in the peripheral nervous system?

A. Microglia

B. Astrocytes

C. Schwann cells

D. Oligodendrocytes

Answer 20

C. Schwann cells

Schwann cells produce myelin in the peripheral nervous system

In the central nervous system, oligodendrocytes produce myelin.

Question 21

_________ support and brace the neurons and anchor them to their nutrient supply lines. They also play an important role in making exchanges between capillaries and neurons.

Answer 21

Astrocytes support and brace the neurons and anchor them to their nutrient supply lines. They also play an important role in making exchanges between capillaries and neurons.

Question 22

________ cells monitor and maintain the health of neurons by detecting injuries to the neuron.

Answer 22

Microglial cells monitor and maintain the health of neurons by detecting injuries to the neuron.

Question 23

Osmotic pressure Π is given by the relation:

Π = iMRT

where i is the van’t Hoff factor, M is the concentration of solute, R is the gas constant, and T is the temperature. The osmotic pressure of sea water is approximately 24 atm at 25°C. What is the approximate concentration of salt in sea water (approximated by NaCl with i = 2)? (Note: Use R = 0.08 L•atm/mol•K.)

A. 0.25 M

B. 0.50 M

C. 0.75 M

D. 1.0 M

Answer 23

B. 0.50 M

The answer to this question is B since algebraic manipulation of the relation gives

M = Π/iRT

= 24 atm / (2 × 0.08 L•atm/mol•K × 300 K)

= 24 / (2 × 24) mol/L

= 0.5 M.

Question 24

A prion is best described as an infectious:

A. prokaryote.

B. transposon.

C. protein.

D. virus.

Answer 24

C. protein

A prion is an abnormally folded protein that induces a normally folded version of the protein to also adopt the abnormal structure, which is often deleterious.

Question 25

Define:

Prions

Answer 25

Prions are infectious proteins.

They are misfolded proteins that cause other proteins to become misfolded, with implications for cellular function.

Creutzfeldt-Jakob disease (human form of “mad cow disease”), fatal familial insomnia, and kuru (transmitted by cannibalism) are all caused by prions

Question 26

Define:

Viroids

Answer 26

Viroids are small infectious particles found in plants that can silence gene expression by binding to specific RNA sequences

Question 27

Assume that S. typhi immediately enters the bloodstream from the small intestine. Of the following, which would be the first major organ that bloodborne S. typhi would encounter?

A. Stomach

B. Pancreas

C. Large intestine

D. Liver

Answer 27

D. Liver

The answer to this question is D because blood from the small intestine is transported first to the liver, which regulates nutrient distribution and removes toxins from the blood.

Question 28

Which molecule is NOT formed during the citric acid cycle?

A. Malate

B. Succinate

C. α-Ketoglutarate

D. Phosphoenolpyruvate

Answer 28

D. Phosphoenolpyruvate

The answer to this question is D because phosphoenolpyruvate is a product of glycolysis, not the citric acid cycle.

Question 29

Under anaerobic conditions, how many net molecules of ATP are produced by the consumption of 5 moles of glucose?

A. 3 × 10²⁴

B. 6 × 10²⁴

C. 9 × 10²⁴

D. 1.2 × 10²⁵

Answer 29

B. 6 × 10²⁴

Under anaerobic conditions, 2 moles of ATP are produced from each mole of glucose. Thus, 10 moles of ATP would be generated from 5 moles of glucose.

Since there are 6 × 10²³ molecules per mole, 10 moles of ATP is equal to 6 × 10²⁴ molecules.

Question 30

In humans, eggs and sperm are most similar with respect to:

A. cell size.

B. genome size.

C. the time required for development.

D. the numbers produced by a single individual.

Answer 30

B. genome size.

The answer to this question is B because both eggs and sperm contain a haploid number of chromosomes and therefore they are most similar with respect to their genome size.

Question 31

In humans, the characteristic tissue of which of the following organs is NOT derived from mesoderm?

A. Brain

B. Heart

C. Kidney

D. Skeletal muscle

Answer 31

A. Brain

Question 32

Binding to the _______ insinuates we’re affecting synthesis at the transcriptional, or mRNA, level.

Answer 32

Binding to the promoter insinuates we’re affecting synthesis at the transcriptional, or mRNA, level.

Question 33

Where in the human male reproductive system do the gametes become motile and capable of fertilization?

A. Testis

B. Urethra

C. Epididymis

D. Prostate gland

Answer 33

C. Epididymis

Question 34

Which of the following associations between a hormone and its category is INCORRECT?

• *A.** Aldosterone—mineralocorticoid
• *B.** Testosterone—cortical sex hormone
• *C.** ADH—mineralocorticoid
• *D**. Cortisone—glucocorticoid

Answer 34

C
Unlike the other hormones listed here, ADH is not secreted by the adrenal cortex and is therefore not a –corticoid. Rather, ADH is a peptide hormone produced by the hypothalamus and released by the posterior pituitary that promotes water reabsorption. The other associations are all correct.

Question 35

Which of the following hormones directly stimulates a target tissue that is NOT an endocrine organ?

• *A.** ACTH
• *B.** TSH
• *C.** LH
• *D.** GH

Answer 35

D
A hormone that directly stimulates a non-endocrine target tissue is referred to as a direct hormone.

Glancing at the answer choices, we notice that all of the hormones are secreted by the anterior pituitary gland. The direct hormones secreted by the anterior pituitary are prolactin, endorphins, and growth hormone (GH). All of the other answer choices are tropic hormones.

The tropic hormones of the anterior pituitary include follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), and thyroid-stimulating hormone (TSH).

Question 36

Which of the following statements concerning growth hormone is NOT true?

• *A.** Overproduction of growth hormone in adults results in acromegaly.
• *B.** It promotes growth of bone and muscle.
• *C.** It is produced by the hypothalamus but secreted by the pituitary.
• *D.** A childhood deficiency in growth hormone results in dwarfism.

Answer 36

C
Growth hormone is a direct hormone secreted by the anterior pituitary. Among its many functions, GH promotes growth of bone and muscle, eliminating (B).

An overproduction of growth hormone in children results in gigantism, whereas in adults it results in acromegaly (enlargement of the small bones in the extremities and of certain facial bones, such as the jaw), eliminating (A).

On the other hand, a childhood deficiency of growth hormone results in dwarfism, eliminating (D).

GH is synthesized and secreted in the anterior pituitary; (C) describes antidiuretic hormone and oxytocin, not GH.

Question 37

Which of the following hormones is NOT derived from cholesterol?

• *A.** Aldosterone
• *B.** Estrogen
• *C.** Oxytocin
• *D.** Progesterone

Answer 37

C
Steroid hormones are derived from cholesterol. Many of their names end with –one, –ol, or –oid, and they include the hormones of the adrenal cortex and gonads. Aldosterone is a mineralocorticoid from the adrenal cortex, while estrogen and progesterone are sex hormones from the ovaries, eliminating (A), (B), and (D).

Oxytocin is a peptide hormone and is thus not derived from cholesterol.

Peptide and amino acid–derivative hormones often end with –in or –ine.

Question 38

Which of the following is true regarding pancreatic somatostatin?

• *A.** Its secretion is increased by low blood glucose.
• *B.** It is always inhibitory.
• *C.** It is regulated by cortisol levels.
• *D.** It stimulates insulin and glucagon secretion.

Answer 38

B
Pancreatic somatostatin secretion is increased by high blood glucose or amino acid levels, leading to decreased insulin and glucagon secretion, eliminating (A) and (D). Somatostatin is thus always an inhibitory hormone, confirming (B).

The stimuli for somatostatin release include high blood glucose or amino acids, as mentioned above, as well as high levels of certain gastrointestinal hormones —- but not cortisol, eliminating (C).

Question 39

Destruction of all β-cells in the pancreas would cause:

• *A.** glucagon secretion to stop and an increase in blood glucose concentration.
• *B.** glucagon secretion to stop and a decrease in blood glucose concentration.
• *C.** insulin secretion to stop and an increase in blood glucose concentration.
• *D.** insulin secretion to stop and a decrease in blood glucose concentration.

Answer 39

C
β-cells are responsible for insulin production. The function of insulin is to lower blood glucose levels by promoting the influx of glucose into cells and by stimulating anabolic processes, such as glycogenesis or fat and protein synthesis. Thus, destruction of the β-cells would result in a cessation of insulin production, which would lead to hyperglycemia, or high blood glucose concentration.

Question 40

A scientist discovers a new hormone that is relatively large in size and triggers the conversion of ATP to cAMP. Which of the following best describes the type of hormone that was discovered?

• *A.** Amino acid–derivative hormone
• *B.** Peptide hormone
• *C.** Steroid hormone
• *D.** Tropic hormone

Answer 40

B
The question stem indicates that the newly discovered hormone functions as a first messenger, stimulating the conversion of ATP to cAMP; cAMP functions as a second messenger, triggering a signaling cascade in the cell. Hormones that act via second messengers and are relatively large in size (short peptides or complex polypeptides) are peptide hormones.

This hormone could be a tropic hormone, but it is also entirely possible for it to be a direct hormone; thus, (D) can be eliminated.

Question 41

Oxytocin and antidiuretic hormone are:

• *A.** peptide hormones produced and released by the pituitary.
• *B.** steroid hormones produced and released by the pituitary.
• *C.** peptide hormones produced by the hypothalamus and released by the pituitary.
• *D.** steroid hormones produced by the hypothalamus and released by the pituitary.

Answer 41

C
Both oxytocin and vasopressin (another name for antidiuretic hormone) end with the suffix –in; this should hint that they are peptide or amino acid–derivative hormones. These two hormones are both synthesized by the hypothalamus, but released by the posterior pituitary.

Remember that the posterior pituitary does not actually synthesize any hormones itself; rather, it contains the axons that originate in cells in the hypothalamus and is the site of release for these hormones.

Question 42

Excessive levels of dopamine in the brain are associated with psychosis. Accordingly, many antipsychotic medications block dopamine receptors. Which of the following effects may be seen in an individual taking antipsychotics?

• *A.** Increased secretion of growth hormone
• *B.** Decreased secretion of growth hormone
• *C.** Increased secretion of prolactin
• *D.** Decreased secretion of prolactin

Answer 42

C
Dopamine is used in a number of neurological systems; most relevant to the endocrine system is the fact that dopamine secretion prevents prolactin release. Thus, an individual taking medications that block dopamine receptors would lose this inhibition on prolactin release and have elevated prolactin levels.

Question 43

A genotypically female infant is born with ambiguous genitalia. Soon after birth, she suffers from hyponatremia, or low blood concentrations of sodium. Which endocrine organ is most likely to be affected?

• *A.** Hypothalamus
• *B.** Pituitary
• *C.** Kidneys
• *D.** Adrenal cortex

Answer 43

D
The question stem states that an infant who is genotypically female is born with ambiguous genitalia, meaning that the genitalia do not appear to be specifically female or specifically male. In a genotypic female, this indicates that she was exposed to androgens during the fetal period. In addition, she is also losing sodium, causing hyponatremia. This indicates that she has two defects. First, she has excess androgens. Second, she is lacking in aldosterone, a hormone required for proper reuptake of sodium in the kidneys. Both of these hormones are synthesized in the adrenal cortex, making (D) the correct answer.

Note that neither of these hormones is regulated by the hypothalamic–pituitary–adrenal axis, eliminating (A) and (B).

Question 44

According to the cross-bridge model of muscle contraction, the muscles stiffen after death because ATP is unavailable to bind and directly release:

A. ADP from the actin head.

B. ADP from the myosin head.

C. the actin head from the myosin filament.

D. the myosin head from the actin filament.

Answer 44

D. the myosin head from the actin filament.

The answer to this question is D because during normal muscle contraction, ATP is required to break the bonds between the actin filament and the myosin head. After death, no new ATP is generated, so the myosin head cannot be released from the actin filament, resulting in stiffening of muscles.

Question 45

A homodimeric protein was found to migrate through SDS polyacrylamide gel electrophoresis (SDS-PAGE) with a mobility that matched that of a 45-kDa standard. What change in the experiment would increase the chances of observing the mobility expected for the 22.5-kDa monomer?

A. Increasing the gel running time

B. Adding a reducing agent

C. Using a higher voltage

D. Removing the SDS

Answer 45

B. Adding a reducing agent

The answer to this question is B because adding a reducing agent would eliminate any disulfide bridges and allow the monomers to run separately–thus leading to a migration expected for the 22.5-kDa protein.

Question 46

True or false:

I**n vivo, reactions that have positive ΔGº values cannot proceed forward without an external source of energy.

Answer 46

This statement is false.

Reactions with positive ΔGº values are nonspontaneous under standard conditions. However, they can sometimes occur spontaneously inside cells (e.g., under nonstandard conditions) when the ratio of products to reactants is sufficiently small. This is an important strategy that cells use to drive nonspontaneous reactions forward.

Question 47

Do exergonic reactions require work done on the reaction system at any point?

Answer 47

Exergonic reactions generate energy that can be used to do work. They do not consume energy, so they do not require external work.

Question 48

Define:

Gibbs Free Energy

Answer 48

Gibbs free energy is the amount of energy available in a system which can be used to do work

Question 49

True or False:

Reaction conditions can affect both the magnitude and sign of ΔG

Answer 49

True

ΔG = ΔG^o + RTln(Q)

The free energy change under any set of conditions is the sum of the standard free energy change and RTlnQ, where R is the gas constant, T is absolute temperature and Q represents the reaction quotient ( a ratio of product concentration to reactant concentration, raised to their respective stoichiometric powers).

Question 50

True or false:

For any given reversible chemical reaction (A ↔ B), the endergonic reaction will always have a higher activation energy barrier than the exergonic reverse reaction.

Answer 50

This statement is true.

Generally speaking, all reactions require at least a little activation energy because the transition state is at a higher energy level than the reactants and products. However, for a given chemical process, the endergonic reaction will require more activation energy than the exergonic reverse reaction because the activation energy of an endergonic process is the sum of the energy difference between the products and reactants and the activation energy of the exergonic reaction.

Question 51

Tautomerization can include conversion between:

I. ketone and enol

II. aldehyde and enol

III. enamine and imine

IV. enamine and imide

Answer 51

I, II, and III

Question 52

True or false:

Actin is an ATPase that hydrolyzes its bound ATP.

Answer 52

This statement is true.

ATP-G-actin binds preferrentially to the positive end of an F-actin filament. Subsequently, F-actin catalyzes hydrolysis of its ATP to ADP and inorganic phosphate. Since ATPases are enzymes that hydrolyze ATP (break it down into ADP and inorganic phosphate, releasing energy), actin is technically an ATPase.

Question 53

A single microtubule is composed of how many protofilaments?

Answer 53

13 long, linear protofilaments composed of tubulin dimers come together to form a hollow microtubule.

Question 54

True or False:

Microtubules are ATP-ases

Answer 54

FALSE.

Tubulins are GTP-ases.

Question 55

True or False:

Actin filaments contribute to cell-cell adhesion

Answer 55

False.

Cell-cell adhesion is a major role of intermediate filaments, not actin filaments.

Question 56

What is a major difference in the rigidity of microfilaments and intermediate filaments?

Answer 56

Unlike microfilaments, which are structurally rigid, intermediate filaments are extremely flexible and can be stretched to several times their resting length.

Question 57

True or false:

Most biomolecules travel through the cytosol by diffusion.

Answer 57

This statement is false.

Diffusion is incredibly slow and does not provide a driving source to move molecules in a specific direction. In addition, many biomolecules (such as mRNA) are rapidly degraded when unprotected in the cytosol. Instead, most biomolecules are trafficked along cytoskeletal filaments by motor proteins. This method of transit is much more efficient and specifically directed than diffusion.

Question 58

Integrins contribute in a way that no other cell adhesion molecules (CAMs) can. What is this contribution?

Answer 58

Cell signaling

Integrins modulate many important signaling pathways that function in processes like cell division, differentiation, and apoptosis.

Question 59

How do selectins play a role in the immune response?

Answer 59

Epithelial cells express selectins to trap leukocytes traveling in the bloodstream and divert them to infected tissue.

If selectin expression is reduced, leukocytes recruitment would diminish.

Question 60

True or false:

Tight junctions are less permeable to solutes than are lipid bilayers.

Answer 60

This statement is true.

Tight junctions link cells together very tightly to prevent movement of solutes between them. Cells linked by many tight junctions become a nearly impassable barrier.

For example, the blood brain barrier is made up by tight junctions, and it is harder to pass through than a plasma membrane (which is a lipid bilayer).

Question 61

Describe the major process and function of selectins

Answer 61

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.

Question 62

Explain the role of cadherins and through what junctions they function

Answer 62

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

Question 63

Explain the role of integrins

Answer 63

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

Integrins modulate many important signaling pathways that function in processes like cell division, differentiation, and apoptosis.

Question 64

Desmosomes are different from adherens junctions in that they:

Answer 64

Interact with intermediate filaments

Desmosomes are very similar to adherens junctions except that they connect one cell’s intermediate filaments to the cytoskeleton of another cell or to the extracellular matrix.

Adherens junctions interact with actin filaments rather than intermediate filaments.

Question 65

B cells employ immunoglobulin class switching to change an antibody’s isotype class. This process involves:

Answer 65

Modifying the antibody’s constant domain.

In class switching, B cells change the production of one antibody isotype to another with a modified constant domain, the bottommost region of the antibody that interacts with other host proteins. For example, an IgA antibody is secreted mainly in mucous membranes. If the immune system wants to eliminate its target pathogen in other areas of the body, it might modify production into an IgG isotype, which is more broadly expressed.

Question 66

Antibody isotypes are differentiated at what portion of the structure?

Answer 66

Different Ig isotypes serve different roles in the adaptive immune system. They are distinguished by the constant domain region of their heavy chains.

Question 67

True or False:

Antibodies are glycoproteins

Answer 67

True

Since antibodies are proteins with attached carbohydrate components, they are considered glycoproteins.

Question 68

True or false:

Antibodies are always secreted as Ig monomers.

Answer 68

This statement is false.

Antibodies are certainly released as monomers, but can also be secreted as dimers, tetramers, and pentamers. To form these polymers, individual Ig units are linked through their constant domains.

Question 69

True or false:

The polymerization of G-actin is accompanied by the hydrolysis of ATP.

Answer 69

This statement is true.

G-actin monomers hydrolyze ATP as they add to a growing F-actin strand. This results in a transient “ATP cap” at one end of a microfilament and a less stable “ADP cap” at the other end.

Question 70

What does an IgD antibody do?

Answer 70

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.

Question 71

What motor protein is associated with motility of eukaryotic flagella?

Answer 71

Axonemal dyneins generate the sliding motion between microtubules that is necessary for the movement of eukaryotic cilia and flagella.

Question 72

Cadherins form what two cell junctions?

Answer 72

Desmosomes and Adherens

Desmosomes are made of cadherins. In this type of anchoring junction, cadherins connect a cells’ intermediate filaments to other cells.

Like desmosomes, adherens junctions are made of cadherin. Here, cadherins interact with cytoskeletal actin filaments rather than intermediate filaments.

Question 73

True or false:

The hypervariable region of an Ig heavy chain must be modified during class switching.

Answer 73

This statement is false.

An antibody’s hypervariable regions are extremely specific and define which antigen it targets. When an antibody undergoes class switching, a B cell changes production to a different Ig isotype with modified constant regions of its heavy chains, not its hypervariable regions.

Question 74

True or False:

A preparative purification tends to result in a smaller amount of protein than an analytical purification.

Answer 74

This statement is false.

A preparative purification is employed when a researcher wishes to have a large amount of the desired protein, while an analytical purification is used when a researcher desires a small, very pure protein extract for qualitative analysis.

Question 75

True or false:

An electrophoresis apparatus is an example of a galvanic cell.

Answer 75

This statement is false.

An electrophoresis apparatus is an example of an electrolytic cell, as it has a positively-charged anode, a negatively-charged cathode, and applies current to drive a non-spontaneous reaction.

Question 76

The Beer-Lambert law describes the relationship between what two properties?

Answer 76

Solute concentration and absorbance of light.

They display a directly proportional relationship

Question 77

What are the functions of HDL and LDL, respectively?

Answer 77

HDL delivers cholesterol to the liver

LDL delivers cholesterol to the body tissues

Question 78

True or false:

A trans unsaturated fatty acid has a melt temperature more similar to a cis unsaturated fatty acid than to a saturated fatty acid of the same chain length.

Answer 78

This statement is false.

Fatty acids that contain a trans double bond are incredibly stackable, much like saturated fatty acids. Due to this structural feature, both trans and saturated fatty acids tend to be solid at room temperature.

Since cis double bonds introduce a kink in the fatty acid chain that disrupts intermolecular forces, cis fatty acids tend to have much lower melting points and are typically liquids at room temperature.

Question 79

True or false:

Saponification converts triglycerides into glycerol and fatty acid salts under alkaline conditions.

Answer 79

This statement is true.

During saponification, a strong base like sodium hydroxide cleaves the ester bonds in triglycerides, generating glycerol and fatty acids. Because the carboxylic acid groups on the fatty acids are deprotonated under basic conditions, they associate with sodium ions in solution and are called fatty acid salts.

Question 80

What class of vitamins are derived from cholersterol?

Answer 80

D vitamins.

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

Question 81

True or false:

Waxes are cholesterol derivatives that contain many diverse functional groups, including esters, aromatic ring systems, and alcohols.

Answer 81

This statement is false.

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

Question 82

True or false:

Naturally occurring unsaturated fatty acids tend to have lower melting and boiling points than saturated fatty acids of comparable chain length.

Answer 82

This statement is true.

Most naturally occurring unsaturated fatty acids contain cis double bonds. Cis bonds introduce a bend or kink into the hydrocarbon chain, which prevents chain stacking. This reduces the intermolecular forces between fatty acids, lowering melting and boiling point. Saturated fatty acids tend to have higher melting and boiling points because they can pack together more tightly.

Question 83

Which of the following lipoproteins has the highest lipid to protein ratio?

A. HDL

B. LDL

C. IDL

D. VLDL

Answer 83

D. VLDL

VLDL stands for “very low-density lipoprotein.” A lipoprotein with a higher protein content is more dense; VLDL is especially rich in lipids resulting in a very low density.

Question 84

True or false:

trans fatty acids are more likely to be solid at room temperature than cis fatty acids.

Answer 84

This statement is true.

Melting and boiling point are determined by intermolecular forces. Fatty acids that contain trans-double bonds are more stackable than fatty acids that contain cis double bonds, which introduce a kink into the chain. Therefore, trans fats are likely to be solid at room temperature.

Question 85

What organ produces the proteins albumin and clotting factors?

Answer 85

The liver produces albumin and clotting factors

Question 86

What peptide hormone stimulates the release of both bile and pancreatic juices and also acts in the brain, where it promotes satiety?

Answer 86

Cholecystokinin (CKK)

Cholecystokinin (CKK) is a peptide hormone that stimulates the release of both bile and pancreatic juices and also acts in the brain, where it promotes satiety.

Question 87

Describe the role of somatostatin

Answer 87

Somatostatin is the main inhibitory hormone in the digestive system. It inhibits all of the major pro-digestion hormones (gastrin, CCK and secretin), slows stomach emptying, and prevents the release of growth hormone, insulin, and glucagon.

Question 88

5 moles of glucose are added to a vial of yeast cells. All appropriate enzymes and coenzymes are present. How many moles of product will be generated?

A. 2 moles of ethanol, 2 moles of CO₂

B. 5 moles of ethanol, 10 moles of CO₂

C. 10 moles of ethanol, 5 moles of CO₂

D. 10 moles of ethanol, 10 moles of CO₂

Answer 88

D. 10 moles of ethanol, 10 moles of CO₂

1 glucose molecule yields 2 ethanol and 2 CO₂ molecules, so following these stoichiometric coefficients shows that 5 moles of glucose would yield 10 moles of each product.

Question 89

Which of the following molecules is most likely to be filtered into the Bowman’s capsule in the kidneys?

A. Leukocytes

B. Plasma proteins

C. Vitamin C

D. Polysaccharides

Answer 89

C. Vitamin C

Vitamin C is water-soluble and is excreted in the urine.

Cells (such as leukocytes), plasma proteins, and chains of carbohydrates are all too large to make it into the Bowman’s capsule and are not excreted in the urine.

Question 90

All of the following are similarities between DNA and RNA EXCEPT:

A. the capacity to hydrogen bond.

B. the ability to catalyze certain biochemical reactions.

C. the role of encoding genetic information.

D. the direction of their synthesis.

Answer 90

B. the ability to catalyze certain biochemical reactions.

Ribozymes are RNA molecules that are capable of catalyzing biochemical reactions, including RNA and DNA ligation and peptide bond formation.

DNA molecules are NOT able to function as enzymes.

Question 91

Can DNA molecules function as enzymes?

Answer 91

No.

But RNA (ribozymes) can.

Question 92

How might failed synapsis affect the daughter cells produced by meiosis?

A. It would create two nonidentical daughter cells rather than two identical ones.

B. It would inevitably lead to the destruction and apoptosis of the daughter cells.

C. Synapsis occurs during mitosis, not meiosis; therefore, it would not affect the daughter cells at all.

D. It could create abnormalities through inversion, translocation, or nondisjunction, disrupting the genetic information of the gamete.

Answer 92

D. It could create abnormalities through inversion, translocation, or nondisjunction, disrupting the genetic information of the gamete.

D is correct. During synapsis, homologous chromosomes pair up together and undergo crossing over. Failure to correctly complete synapsis could be caused by an inversion, translocation, or nondisjunction. The gamete might undergo apoptosis due to being genetically inviable; it could also, however, continue on to complete meiosis. Several genetic diseases in humans are caused by failed synapsis.