AAMC MCAT Exam 4| QUESTIONS & ANSWERS| ALREADY PASSED| VERIFIED & UPDATED

Most cytochrome P450 enzymes alter the activity of drugs by: A. phosphorylating them. B. dephosphorylating them. C. oxidizing them. D. reducing them. - ANSWER C. oxidizing them. cytochrome p450 acts as monooxygenase, where an oxygen atom is inseted into substrate, thereby resulting in oxidation of substrate. 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? - ANSWER A This is the only graph that correctly illustrates a quicker metabolism—or shorter halflife—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). 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? A. Tyrosine B. Serine C. Alanine D. Threonine - ANSWER C. 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. Phosphorylation= tyrosine, serine, and threonine 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: A. bacteriophages consist only of DNA and protein. B. only DNA, not protein, can enter the host cell. C. only protein, not DNA, can enter the host cell. D.