MCAT Prep 2021 questions and answers all correct

MCAT Prep 2021 Gluceogenesis Correct Answer: metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates, used to maintain blood glucose levels Which of the following situations would NOT stimulate gluconeogenesis? A. High glucagon levels B. High levels of AMP C. High levels of citrate D. High levels of acetyl-CoA Correct Answer: B. Wouldn't be A because glucagon is released when blood glucose levels are low and drives pathways toward gluconeogenesis to keep blood glucose levels stable Wouldn't be C or D because high levels of citrate and acetyl-CoA indicate that the Krebs cycle is active and does not need more precursors, so will shift the cell away from glycolysis and toward gluconeogenesis. Think of it as taking these biosynthetic precursors and stashing them for future use. They aren't needed if the Krebs cycle is operating at capacity When is gluceogenesis stimulated? Correct Answer: When energy charge is high and glycolytic and Krebs cycle intermediates are high. If energy is low, and/or Krebs cycle intermediates are low, then glycolysis will be stimulated What do high levels of AMP show? Correct Answer: Indicate that energy charge is low and that ATP needs to be made. AMP inhibits the enzyme fructose-1,6-bisphosphatase, keeping levels of fructose-1,6-bisphosphate high and driving the cell towards glycolysis Proteins are macromolecules formed by joining together individual amino acids. Which of the following is true? A. Protein synthesis proceeds in the N--C direction, joining the carboxyl group carbon of the first amino acid to the amino group nitrogen of the second amino acid. B. Protein synthesis proceeds in the NC direction, joining the amino group nitrogen of the first amino acid to the carboxyl group carbon of the second amino acid. C. Protein synthesis proceeds in the CN direction, joining the carboxyl group carbon of the first amino acid to the amino group nitrogen of the second amino acid. D. Protein synthesis proceeds in the CN direction, joining the amino group nitrogen of the first amino acid to the carboxyl group carbon of the second amino acid. Correct Answer: A. In prokaryotic cellular respiration, which of the following processes occur in the cytoplasm? I. Glycolysis II. Pyruvate decarboxylation (via the PDC) III. Krebs cycle A. I only B. I and II only C. II and III only D. I, II, and III Correct Answer: D. Since prokaryotes (bacteria) lack cellular organelles, all of cellular respiration takes place in the cytoplasm. Electron transport occurs across the cell membrane. Statements I, II, and III are all true. Where does cellular respiration occur in prokaryotes? Correct Answer: Cytoplasm In the translation of a fifty-amino acid peptide, which of the following steps requires the greatest overall amount of energy? A. tRNA loading B. Initiation C. Translocation D. Termination Correct Answer: A. The most energy-intensive process in translation involves the attachment of amino acids to their corresponding tRNAs, also known as tRNA loading. What is termination in translation and transcription? Correct Answer: Termination involves the binding of a release factor to a stop codon and does not directly require any energy A non-competitive inhibitor: I. binds to an allosteric site. II. reduces the Vmax of a reaction. III. can be overcome by adding more substrate. A. I only B. I and II only C. II and III only D. I, II, and III Correct Answer: B. Where do non-competitive inhibitors bind to? And what do they prevent? Correct Answer: Allosteric sites and prevent enzyme from catalyzing the reaction Does a non-competitive inhibitor reduce the Vmax of a reaction? Correct Answer: Yes, it lowers the enzyme concentration and that lowers the Vmax Can non-competitive inhibition be overcome by adding more substrate? Correct Answer: No, this only happens in competitive inhibition where the inhibitor and substrate both bind to the active site. Which of the following alterations to the lac operon in E. coli would negatively impact the cell's ability to utilize lactose as an energy source? A. A single amino acid substitution in the repressor's lactose binding site, preventing lactose binding B. A single nucleotide mutation in the operator, blocking repressor association C. A mutation in the DNA binding site of the repressor, markedly reducing its ability to bind to DNA D. A mutation resulting in the constitutive expression of the repressor Correct Answer: A. Any alteration that would decrease the expression of the genes necessary for lactose transport and breakdown would negatively impact the cell's ability to utilize lactose as an energy source. If the lactose binding site on the repressor could no longer bind lactose, the repressor would be able to bind to the operator region on DNA, but the presence of lactose would no longer cause dissociation of the repressor, and transcription of the necessary genes would not occur (choice A is correct). If a mutation occurred in the operator which prevented repressor binding, transcription of the lac operon genes would always occur (choice B is wrong). Similarly, a mutation in the DNA binding site of the repressor that prevented it from binding to DNA would lead to constitutive gene expression (choice C is wrong). Increased expression of the repressor itself would not necessarily decrease transcription of the lac operon genes, assuming that the regulation of the repressor by lactose is not affected (choice D is wrong). A reaction with a negative ΔG is: A. spontaneous and has a rapid rate. B. non-spontaneous and has a slow rate. C. spontaneous and may or may not have a rapid rate. D. non-spontaneous and may or may not have a rapid rate. Correct Answer: C.