MCAT Biology Diagnostic Exam 1A Questions and Answers

MCAT Biology Diagnostic Exam 1A Questions and Answers Define spontaneous reaction - Correct Answer️️ -exergonic Vmax is determined by - Correct Answer️️ -enzyme concentration What type of reaction most commonly creates polymers from macromolecules - Correct Answer️️ -dehydration synthesis Most common process by which enzyme activity is regulated - Correct Answer️️ - negative feedback loop In cellular respiration, what acts as the final electron acceptor if O2 is not available - Correct Answer️️ -pyruvate How many net ATPs are produced when a prokaryotic cell fully oxidizes one molecule of glucose? - Correct Answer️️ -32 Which of the following situations would NOT stimulate gluconeogenesis? -High glucagon levels -High levels of AMP -High levels of citrate -High levels of acetyl-CoA - Correct Answer️️ -High levels of AMP B. Gluconeogenesis will be stimulated 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. High levels of AMP 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 (choice B would not stimulate gluconeogenesis and is the correct answer choice). 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 (choices C and D would stimulate gluconeogenesis and can be eliminated). Glucagon is released when blood glucose levels are low and drives pathways toward gluconeogenesis to keep blood glucose levels stable (choice A would stimulate gluconeogenesis and can be eliminated). Proteins are macromolecules formed by joining together individual amino acids. Which of the following is true? A) Protein synthesis proceeds in the NC 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 Answer️️ -A. Protein synthesis proceeds in the NC direction; the next amino acid in the sequence is added to the free carboxy terminus of the growing peptide (choices C and D are wrong). The carbon of the carboxyl group on the first amino acid (or on the polypeptide) is joined to the nitrogen of the amino group on the incoming amino acid (choice A is correct and choice B is wrong). In prokaryotic cellular respiration, which of the following processes occur in the cytoplasm? Glycolysis Pyruvate decarboxylation (via the PDC) Krebs cycle A) I only B) I and II only C) II and III only D) I, II, and III - Correct Answer️️ -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. 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 Answer️️ -A. The most energy-intensive process in translation involves the attachment of amino acids to their corresponding tRNAs, also known as tRNA loading (or tRNA charging, or amino acid activation). This requires two high- energy phosphate bonds per aa-tRNA pair (choice A is correct). Initiation requires only 1 GTP (choice B is wrong). Elongation includes A-site binding and translocation (for amino acid number two and onwards); one GTP is hydrolyzed to bring an aa-tRNA into the A site, and one GTP is required for translocation (choice C is wrong). Termination involves the binding of a release factor to a stop codon and does not directly require any energy (choice D is wrong). In this example, it would require 100 ATP to charge a sufficient number of tRNAs to generate the peptide, 1 GTP for initiation, 49 GT