AAMC 4 Bio question with complete solution 2023/2024

AAMC 4 Bio question with complete solution 2023/2024Most cytochrome P450 enzymes alter the activity of drugs by: - correct answer oxidizing them *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. - MISSED - was between reduced and oxidized; remember it is a monoxygenase During phosphorylation of STAT5b proteins, phosphate groups are exchanged for what atoms on tyrosine residues? - correct answer Hydrogen atoms of hydroxyl groups -MISSED *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. * I read the question wrong, i thought it was asking what the phosphate groups would attach to being the oxygen bc of nucleophilic attack but its asking what it replaces which leaves the hydrogen. 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 answer A. *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). - MISSED..IM SO SILLY i knew this but missed the estrogen -sensitive part in the question A defining characteristic of proteins that act as transcription factors (such as STAT5b) is that they: - correct answer contain a DNA binding domain. *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 answer mitochondria * 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 answer 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. * tricky During the ACC1- or ACC2-catalyzed formation of malonyl-CoA, what is the structure of the functional group added to acetyl-CoA? - correct answer c. *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 answer alanine *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 answer only DNA, not protein, can enter the host cell. *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 answer Two ATP molecules consumed, four ATP molecules produced *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 answer decreases as a result of a decrease in plasma pH. *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 answer Partial pressure of the gas *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. GUESSED RIGHT 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 answer 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 answer more than 87 nucleotides - MISSED *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. **SILLY MISTAKE OMG i misread..i cant even explain why i chose a 28 x 3= 84 +3 (stop codon) + rest of peptide > 87 Hormone replacement therapy is often given to children who have Prader-Willi syndrome once they have reached the hyperphagic stage. Based on the passage, the most likely reason for this therapy would be to prevent: - correct answer short stature -MISSED *Prader-Willi syndrome is characterized by growth hormone deficiency. Thus, hormone replacement therapy will prevent short stature. *shouldve gotten this right- in passage Eating suppresses ghrelin secretion. However, this suppression does not appear to be caused by the presence of food in the stomach or duodenum, nor by stomach distension. Given this, which of the following physiological conditions is likely to suppress ghrelin secretion following a meal? - correct answer Increased levels of circulating insulin * The levels of circulating insulin will increase after a meal due to an increase in blood glucose levels. Assume that a certain individual has no underlying metabolic disorder and has a normal ghrelin response. Given this, what would most likely happen to this individual's fasting level of circulating ghrelin if the individual were to first gain, then lose, a significant amount of weight by natural methods? - correct answer decrease as the individual gained weight, then increase as the individual lost weight. *Because of a feedback mechanism, the levels of circulating ghrelin are the opposite of the amount of weight gained. They are low when the individual gains weight and high when the individual loses weight. Based on the passage, which subunit of PTx is LEAST suitable for generation of vaccine against B. pertussis? - correct answer S1 *When choosing an antigen for vaccine production, there are two aspects to consider: immunogenicity and toxicity. S1 has the ADP ribosyl transferase activity responsible for toxicity of PTx and therefore is least suitable for vaccine production. ** all the other subunits were part of the component that binds to the cell surface Erythromycin interferes with protein synthesis by binding to which ribosomal subunit? - correct answer 50S *Based on the passage, erythromycin inhibits bacterial protein synthesis by binding to the 23S rRNA component of the large subunit of the bacterial ribosome. The large subunit of the bacterial ribosome has a sedimentation coefficient of 50 Svedberg (S). (20S for small; 70S for intact) Substituting the residue at position 54 of BvgA with which amino acid will LEAST likely prevent the expression of the PTx operon? - correct answer Glutamate *The passage notes that the residue at position 54 of BvgA is an aspartate (D54). As glutamate and aspartate both carry a negative charge at physiological pH, a substitution of glutamate for an aspartate is the most conservative and least likely to affect the BvgA promoter binding and the expression of the PTx operon. Binding of erythromycin to the large subunit of the bacterial ribosome most likely blocks the transfer of the tRNA bound at: - correct answer the A site to the P site of the ribosome. *The passage notes that binding of erythromycin to the 23S rRNA component of the large subunit of the bacterial ribosome interferes with aminoacyl transferase function, preventing tRNA transfer between the tRNA sites of the ribosome. During protein translation, aminoacyl transferase functions to transfer the tRNA originally bound at the A (amino acid) site to the P (peptide) site and later to the E (exit) site of the ribosome. This option follows this order of transfer. Which compound is predicted to mimic the effect of exercise in undifferentiated muscle cells in vivo? - correct answer An antagonist of TNF-α signaling - MISSED *The passage notes that MYOD1 upregulates muscle cell differentiation by induction of Cdkn1a levels. Figure 1 shows that CTS, a simulator of exercise, upregulates MYOD1 mRNA levels, inferring that it is a positive regulator of muscle cell differentiation. The figure also shows that TNF-α downregulates the MYOD1 mRNA levels, inferring that it is a negative regulator of muscle cell differentiation. Therefore, it can be predicted that an antagonist of TNF-α (a negative regulator muscle cell differentiation) would mimic the effect of exercise (a positive regulator of muscle cell differentiation). Which Lineweaver-Burk plot best illustrates the enzymatic kinetics of NOS in the presence (+I) or absence of (-I) of L-NAME? - correct answer B *The passage states that L-NAME is a competitive inhibitor of NOS activity. This option illustrates a Lineweaver-Burk plot corresponding to competitive inhibition. Which experiment can be used to investigate the transcriptional regulation of the Cdkn1a protein? - correct answer Assessing Cdkn1a mRNA levels by RT-PCR - MISSED *As the question is focused on the transcriptional regulation, it is logical to assess the mRNA levels as opposed to protein levels. RT-PCR is a molecular technique that measures mRNA levels of specific protein. * MISREAD- i thought it was referring to the protein and missed the "transcriptional regulation" aspect that clearly refers to mRNA At physiological pH, what is the net charge of the nuclear localization sequence described in the passage? - correct answer 0 *Based on the passage, the sequence of the nuclear localization sequence of MYOD1 is NDAFEITKRC. At physiological pH, the nuclear localization sequence of MYOD1 (NDAFEITKRC) contains three positively charged amino acids (K, R, and the N-terminal amino acid) and three negatively charged amino acids (D, E, and the C-terminal amino acid). Therefore, the net charge of this sequence at physiological pH is zero. Which conclusion can be drawn from the data presented in Figure 1? In myoblast cells: - correct answer a biomechanical stimulus reverses the effects of inflammatory cytokines. *Based on data shown in Figure 1, inflammatory cytokines (TNF-α) reduce MYOD1 mRNA levels (comparing the third column with first column). Treating cells with biomechanical stimuli (CTS) reverses the effects of inflammatory cytokines (TNF-α). This reversal is shown by comparing the fourth column with the third one. The nuclear localization sequence of MYOD1 contains how many potential phosphorylation sites? - correct answer one - MISSED *There are three amino acids that are phosphorylated in eukaryotes: serine (S), threonine (T), and tyrosine (Y). The nuclear localization sequence of MYOD1 (NDAFEITKRC) contains one threonine (T) that can potentially Which technique separates proteins independently of their charge? - correct answer Gel filtration chromatography - MISSED * Gel filtration chromatography separates protein only on the basis of their size. * silly mistake.. i knew this - gels trap the small molecules and the big ones elute first !!Native PAGE is used to separate molecules based on their electrophoretic mobility, relying on length, conformation, and charge. A peptide consisting of nine amino acids was partially hydrolysed. Three different tripeptides were isolated. None of the tripeptides share a common amino acid. Based on the data, what is the total number of possible structures possible for the full-length peptide? - correct answer 6 - MISSED * If the sequences were ABC, DEF, and GHI, they can only be joined in 6 different possible ways to make a nonapeptide. Each of the tripeptides can appear in the first position and can combine in two possible ways with the other two tripeptides: 3 × 2 x 1 = 6. * trickk question A woman with cystic fibrosis considers having children with an asymptomatic man who is heterozygous for the cystic fibrosis allele. What is probability of having a child with cystic fibrosis? - correct answer 50% * A heterozygous genotype that results in an asymptomatic phenotype implies that the disorder is due to a recessive allele. Therefore, a homozygous individual and a heterozygous individual have 50% probability of having a child with the disorder. Which of the following statements best applies to the inactive X chromosome in mammalian females? - correct answer It is one of the last chromosomes to replicate. * guessed right Which of the following explains why increasing the initial concentration of pyruvate will cause an increase in the equilibrium concentration of acetylphosphate? - correct answer Le chateliers principle * Based on Reaction 1, pyruvate and acetylphosphate are the reactant and product of the reaction, respectively. Le Châtelier's principle states that increasing the concentration of a reactant (pyruvate) will increase the concentration of a product (acetylphospate) at equilibrium. What is the equilibrium constant expression for Reaction 1? - correct answer [Acetylphosphate][CO2][H2O2]/[Pyruvate][Pi][O2] *The equilibrium constant expression can be formulated by the Law of Mass Action: [products]/[reactants] with each component raised to a power equal to their stoichiometric coefficient. Water, as liquid and solvent, does not appear in the expression. The negative control used in Experiment 1 was most likely: - correct answer unconditioned media with AECs. *A negative control is the one that is performed in the conditions that are not expected to give positive results. Thus, unconditioned media will need to be used. As antibodies are highly specific, if 53BP1 and γH2AX are detected in the negative control, this means that AEC are present. Which experiment would best link the result of experiments 1 and 2 to show that S. pneumoniae can cause apoptosis of host cells by contributing to DSBs? - correct answer Measure levels of H2O2 produced by each strain. *Experiment 1 suggests that secreted factors from S. pneumoniae strains cause DSBs. Experiment 2 suggests that exposure to H2O2 induces apoptosis. An experiment that links the results obtained from these two independent experiments would be to confirm that the S. pneumoniae strains produce H2O2. The information in the passage best supports the hypothesis that which of the following defects accounts for excessive eating by people who have bulimia? - correct answer Decreased release of CCK in response to food * The passage states that scientists think that a defect in CCK secretion is the cause of bulimia nervosa. In the absence of CCK, there is no negative feedback that can give the sensation of satiety. Which of the following events does the release of CCK likely trigger? - correct answer Contraction of muscle in wall of gallbladder and relaxation of hepatopancreatic sphincter - MISSED * The passage states that in the presence of CCK, more bile is released. For this to happen, the smooth muscles around the gall bladder will have to contract, and the hepatopancreatic sphincter will have to relax. * SILLY mistake i know a sphincter has to relax in order for contents to flow out of it i think i associated the sphincter with the pancreatic juices that come out but thats wrong Which graph best illustrates the change in food consumption that would result from CCK treatment of rats? - correct answer c. *The passage notes that CCK triggers satiety centers within the brain upon ingestion of food and thereby induces a sensation indicating that enough food has been eaten. This graph shows that the CCK-treated rats eat less than the control rats. By stimulating secretion of peptidases from the pancreas into the duodenum, CCK facilitates the digestion of: - correct answer protein On the day of the experiment, the subjects drank about 1 L of water on average and excreted about 400 mL of urine. The most likely explanation for the difference between water intake and urine excretion is that: - correct answer water was excreted via the skin and the lungs. - MISSED * Extra water is normally excreted through skin and lungs. The skin excretes water through the process of transpiration, and the lungs use water to humidify the air that enters the body. - silly mistake i thought it went to the blood volume bc hydration increases bp but the middle graph indicates blood vol not changing also 600mL is too large of a number to go into the blood The osmolarity of urine in these subjects was 958 milliosmoles/L, compared with an average blood osmolarity of 284 milliosmoles/L. The higher osmolarity of urine suggests that: - correct answer the kidneys are acting to conserve water. *An increase in water conservation would result in higher urine osmolarity and lower blood osmolarity. In a different experiment, healthy human volunteers received an intravenous infusion of 100 mL of hyperosmotic NaCl solution, which induced thirst and a desire to drink. In this experiment, thirst probably was stimulated via: - correct answer osmoreceptors, as a result of increased blood osmolarity after the infusion. *Osmoreceptors are activated by the increase in osmolarity of the blood. This process triggers the sensation of thirst. Which of the following responses could maintain cardiac output under dehydration conditions that reduce blood volume? - correct answer An increase in heart rate *The heart rate is the number of heart contractions per minute. An increase in heart rate would maintain the cardiac output in dehydration conditions.