AAMC FL 4: Biology/Biochemistry || with Error-free
Solutions.
Most cytochrome P450 enzymes alter the activity of drugs by: correct answers Cytochrome P450
acts as monooxygenases, where an oxygen atom is inserted into a substrate (the drug of interest),
thereby resulting in the oxidation of the substrate.
During phosphorylation of STAT5b proteins,phosphate groups are exchanged for what atoms on
tyrosine residues? correct answers The passage notes that JAK2 is a tyrosine kinase. Tyrosine
has a nucleophilic hydroxyl group that attacks the terminal phosphate group (γ-PO32-) on ATP,
resulting in the exchange of the hydrogen atom of a hydroxyl group for a phosphate group of
ATP.
Given that antibiotics like erythromycin are metabolized by estrogen-sensitive P450 enzymes
within the liver, which graph best predicts the expected relative half-life of erythromycin in adult
males versus adult females? correct answers This is the only graph that correctly illustrates a
quicker metabolism—or shorter half-life—of erythromycin in females. Given the continuous
presence of GH in females, the cytochrome P450 enzymes are up-regulated, resulting in more
rapid metabolism of certain drugs (like erythromycin). As a result, the half-life of erythromycin
is expected to be lower in females (in other words, it would take less time to metabolize the drug
due to the greater presence of P450 enzymes).
A defining characteristic of proteins that act as transcription factors (such as STAT5b) is that
they: correct answers The defining characteristic of a transcription factor is that it has a DNA-
binding domain that allows it to bind to regulatory nucleic acid sequences in a gene to alter
transcription.
Based on the passage, ACC2 is most likely compartmentalized to: correct answers ACC2 is
involved in fatty acid oxidation, which takes place in the mitochondria.
Based on the passage, as compared to a wild-type mouse, an Acc2-/-/Cpt1-/- double knockout
mouse is most likely to exhibit: correct answers decreased fatty acid oxidation.
CPT1 is an essential enzyme in the carnitine shuttle, transporting fatty acids into the
mitochondria for oxidization. The absence of CPT1 would prevent the transport of fatty acids
into the mitochondria for oxidization, irrespective of the presence or absence of ACC2.
During the ACC1- or ACC2-catalyzed formation of malonyl-CoA, what is the structure of the
functional group added to acetyl-CoA? correct answers According to the passage, ACC1 is a
carboxylase and will convert acetyl-CoA to malonyl-CoA through the addition of a carboxyl
group to acetyl-CoA.
The researchers want to generate a mutant mouse strain that expresses a constantly active variant
of ACC2 by replacing the amino acid at position 212 with a different residue. Which residue is
the best choice as a replacement? correct answers According to the passage, AMPK inactivates
, ACC2 through phosphorylation of the residue at position 212. To create a constitutively active
variant, the residue at position 212 should be substituted with a residue that cannot be
phosphorylated. Of all the amino acids listed, only alanine cannot be phosphorylated.
Bacteriophages were labeled with radioactive phosphorous (32P) and sulfur (35S). The labeled
bacteriophages were then allowed to infect their host cells. At the end of the experiment, the 32P
label was found only inside the host cells and the 35S label was found only outside the host cells.
This experiment shows that: correct answers 32P and 35S incorporate into DNA and proteins,
respectively. Thus, the results of the experiment indicate that only the bacteriophage DNA enters
the cell, not proteins.
Which statement describes ATP consumption and production during the preparatory and payoff
phases of glycolysis, respectively? correct answers Two ATP molecules are consumed in the
preparatory phase during two phosphorylation events. The first reaction converts glucose to
glucose-6-phosphate, and the second reaction converts fructose-6-phosphate to fructose 1,6-
biphosphate. In the payoff phase, four ATP molecules are produced. The first two ATP
molecules are produced in the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, and
another two ATP molecules are produced in the conversion of phosphoenolpyruvate to pyruvate.
As blood passes through actively contracting skeletal muscle tissue, the affinity of hemoglobin
for oxygen in the muscle tissue: correct answers Affinity would decrease with a decrease in
plasma pH, and during prolonged exercise, anaerobic respiration would decrease the plasma pH.
A researcher measures the concentration of CO2(aq) in a solution at equilibrium. Which
additional quantity must be measured in order to calculate the Henry's Law constant kH for the
gas? correct answers The Henry's Law constant kH relates the solubility of a gas S to the
pressure of that gas Pg above the solution and is written as S = kH•Pg. Therefore, in addition to
the concentration of CO2(aq) in a solution at equilibrium, the partial pressure of the gas Pg must
be measured.
Which of the following hypotheses best accounts for the differences in the level of circulating
ghrelin in individuals who are obese with no underlying condition and this level in individuals
who are lean? correct answers Ghrelin secretion is suppressed in individuals who are obese
because their bodies have greater energy stores than do the bodies of individuals who are lean.
Obese individuals have more energy stores than lean individual. For this reason, the levels of
ghrelin, which increases appetite, are lower in obese individuals.
Based on the passage, what can be determined about the composition of the mRNA that encodes
the protein from which ghrelin is cleaved?
It is composed of: correct answers Each amino acid is coded by 3 nucleotides; thus, 84
nucleotides are needed to code for the 28-amino-acid peptide ghrelin. To this number, the triplet
that codes for the STOP codon needs to be added. Therefore, 87 is the minimum number of
nucleotides for the 28-amino-acid peptide ghrelin. However, the passage indicates that ghrelin is
cleaved from a longer peptide chain. For this reason, the total number of nucleotides is higher
than 87.
