Prepare for MCAT Biochemistry with these practice questions and answers. This covers enzymes, metabolism, molecular biology, and biochemical pathways.
Q: a) by decreasing the E(a), enzymes increase both the reaction rate and the total amount of product formed
Answer: Which of the following best describes the function of enzymes?a) by decreasing the E(a), enzymes increase both the reaction rate and the total amount of product formedb) by making the ∆G of the reaction more negative, enzymes increase the amount of product formed per unit timec) by decreasing the energy of the transition state, enzymes increase the amount of product formed per unit timed) by making the ∆G of the reaction more positive, enzymes increase the total amount of product formed
Q: a) C₄H₆O₅
Answer: Malate dehydrogenase is a key enzyme in TCA cycle, which catalyzes the following reaction, which is unfavorable under standard conditions:C₄H₆O₅ + NAD⁺→C₄H₄O₅ + NADH + H⁺Which of the following corresponds to the compound that is most likely to be oxidized under standard conditions?a) C₄H₆O₅b) NAD+c) C₄H₄O₅d) NADH
Q: b) 3 only
Answer: All of the following are examples of oxidation-reduction reactions EXCEPT:1. C₃H₇O₆P + NAD⁺ + P₁→C₃H₈O₁₀P₂ + NADH + H⁺2. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O3. C₆H₁₄O₁₂P₂ → 2C₃H₇O₆Pa) 2 onlyb) 3 onlyc) 1 and 2 onlyd) 1 and 3 only
Q: a) the pKa will decrease due to favorable ionic interactions between the deprotonated Glu and Lys residues
Answer: An acidic Glu residue in a protein (neutral in its protonated form) has pKa value of 2.3 in the wild-type protein and is found near a neutral Ile residue. What will be the effect of the pKa of the Glu residue if a mutation substitutes a positively charged Lys residue for the Ile residue?a) the pKa will decrease due to favorable ionic interactions between the deprotonated Glu and Lys residuesb) the pKa will decrease due to unfavorable ionic interactions between the deprotonated Glu and Lysc) the pKa will increase due to favorable ionic interactions between the deprotonated Glu and Lys residuesd) the pKa will increase due to unfavorable ionic interactions between the deprotonated Glu and Lys residues
Q: c) Lys > Cys > Glu
Answer: Which of the following best orders the relative basicity of the side chains of Glu (pKa=4.1), Cys (pKa=8.3), and Lys (pKa=10.8)a) Cys > Glu > Lysb) Lys > Glu > Cysc) Lys > Cys > Glud) Glu > Cys > Lys
Q: c) it would decrease
Answer: The cells in your body are constantly undergoing cellular respiration, producing CO2 as a byproduct. What would happen to the pH of your blood if you were to hold your breath?a) it would increaseb) it would be the samec) it would decreased) it cannot be determined with the information provided
Q: d) the effect on ∆G cannot be determined without additional information
Answer: If a mutation changed an Arg residue in the protein interior to a Leu residue, what would be the likely effect on the ∆G of protein folding?a) ∆G would become more positiveb) ∆G would become more negativec) ∆G would remain unchangedd) the effect on ∆G cannot be determined without additional information
Q: b) Yes because the net effect would be a loss of active enzyme available for the reaction
Answer: Some inhibitors bind irreversibly to enzymes by covalent attachment. Would the kinetics seen under these conditions be similar to those seen with a reversible noncompetitive inhibitor?a) Yes because it would reduce the K(m) of the reactionb) Yes because the net effect would be a loss of active enzyme available for the reactionc) No because if enough substrate binds to the active site the reaction will reach Vmaxd) No because K(m) will increase and Vmax will stay the same, similar to competitive inhibition
Q: b) a protease
Answer: Some enzymes can modify their substrate, and by this means, regulate its activity. In many instances, these modifications are not permanent since other enzymes can reverse them. Which of the following category of enzymes will irreversibly modify their substrate?a) a kinaseb) a proteasec) a phosphatased) an acetylase
Q: b) increasing the temperature of the enzyme’s surroundings
Answer: Which of the following would have the LEAST effect on the ability of an enzyme to bind its substrate?a) placing an enzyme that optimally functions at pH 7 in a pH 5 solutionb) increasing the temperature of the enzyme’s surroundingsc) mutating the Glu and Asp residues in the active site to Lys and Hisd) changing the substrate from tripeptide to a disaccharide
Q: b) linearly
Answer: For a given enzyme concentration at a low substrate concentration, how does reaction rate change as the substrate concentration increases?a) logarithmicallyb) linearlyc) exponentiallyd) indirectly
Q: d) hemoglobin must consist of multiple protein subunits, whereas myoglobin may or may not consist of multiple protein subunits
Answer: Both hemoglobin and myoglobin are proteins that carry oxygen in the human body. Hemoglobin exhibits cooperativity and is found in red blood cells, whereas myoglobin is not cooperative and is found in muscle cells. Which of the following is likely true regarding these oxygen-carrying proteins?a) the O2 saturation curve will be sigmoidal for myoglobin, but no hemoglobinb) hemoglobin has a lower binding affinity for oxygen than myoglobinc) hemoglobin is used to tightly bind oxygen in the body, while myoglobin is used to deliver oxygen to body cellsd) hemoglobin must consist of multiple protein subunits, whereas myoglobin may or may not consist of multiple protein subunits
Q: a) it will be a series of lines that intersect along the y-axis
Answer: Which of the following will be true of the Lineweaver-Burk plot of an enzyme in the presence of increasing concentrations of a competitive inhibitor?a) it will be a series of lines that intersect along the y-axisb) it will be a series of lines that intersect along the x-axisc) it will be a series of parallel linesd) it will be a series of lines that will intersect, but neither on the y-axis or x-axis
Q: a) glycolysis
Answer: In eukaryotes, the ultimate yield of ATP from NADH is lower when the NADH is produced by:a) glycolysisb) pyruvate dehydrogenase complex (PDC)c) the Krebs Cycled) electron transport and oxidative phosphorylation
Q: c) glycogen contains alpha 1-6 branches every 8-12 monomers, whereas amylose contains alpha 1-6 branches every 12-20 monomers
Answer: Glycogen is a polysaccharide of glucose molecules with alpha 1→4 connections and alpha 1→6 branches. Amylose, a glucose-storing polysaccharide in plants, contains identical linkages, yet is hydrolyzed more slowly than glycogen, Which of the following explains this difference?a) Glycogen adopts a tighter conformation than amylose does in vivob) plant digestive enzymes are specific to Beta linkages and therefore digest the alpha linkages in amylose at a decreased ratec) glycogen contains alpha 1-6 branches every 8-12 monomers, whereas amylose contains alpha 1-6 branches every 12-20 monomersd) amylose’s alpha 1-6 branches require more energy to hydrolyze than those present in glucose
Q: d) overexpression of pyruvate carboxylase
Answer: Which of the following changes would lead to a long-term increase in intracellular glucose levels in liver cells?a) decreased production of glycogen phosphorylaseb) type 1 diabetes mellitus, caused by destruction of the beta cells of the pancreasc) expression of an overactive isoform of the pyruvate dehydrogenase complex (PDC)d) overexpression of pyruvate carboxylase
Q: b) electron transport at the inner mitochondrial membrane would cease
Answer: Salicylic acid (aspirin), if taken in excess, may act as an uncoupling agent. Uncoupling agents increase the permeability of the inner mitochondrial membrane, resulting in the dissipation of the proton gradient. Which of the following would most likely be true in the presence of an uncoupling agent?a) electron transport at the inner mitochondrial membrane would ceaseb) the energy from the proton-motive force would likely be dissipated as heat rather than in producing ATP from ADPc) H+ ions would flow through the inner membrane into the intermembrane spaced) there would be an increase in biosynthesis
Q: c) the pentose phosphate pathway is most active during the M phase of the cell cycle
Answer: Which of the following is FALSE regarding the pentose phosphate pathway?a) a decrease in the NADPH: NADP+ ratio will active the pentose phosphate pathwayb) the pentose phosphate pathway would be upregulated during fatty acid synthesisc) the pentose phosphate pathway is most active during the M phase of the cell cycled) a decrease in the pentose phosphate pathway activity may cause hemolytic anemia (premature destruction of red blood cells)
Q: b) elevated insulin levels deactivate glycogen phosphorylase and activate glycogen synthase
Answer: Glycogen metabolism is regulated by different hormones that activate reciprocal pathways. After several hours of fasting, a person eats a large meal. Which of the following statements is correct?a) elevated glucagon levels deactivate glycogen phosphorylase and active glycogen synthesisb) elevated insulin levels deactivate glycogen phosphorylase and activate glycogen synthasec) elevated glucagon levels activate glycogen phosphorylase and deactivate glycogen synthased) elevated insulin levels activate glycogen phosphorylase and deactivate glycogen synthase
Q: b) NADPH
Answer: Which of the following is a product of the pentose phosphate pathway?a) NADHb) NADPHc) succinyl-CoAd) fructose-6-phosphate
Q: b) carbohydrates exist in a more oxidized state, while lipids are more reduced
Answer: Which property of lipids contributes most to their higher energy density per carbon in comparison to carbohydrates?a) lipids can contain more double bonds in existing carbon chains than carbohydrates can in cyclic structuresb) carbohydrates exist in a more oxidized state, while lipids are more reducedc) carbohydrates are absorbed more easily than lipids by the digestive systemd) lipids can contribute more isoprenes to the Krebs cycle than carbohydrates
Q: c) 3
Answer: Artemisinin, a drug used as part of a multi-valent approach to treating malaria, is a sesquiterpene now being produced in yeast. The biosynthesis of sesquiterpenes requires how many isoprene units?a) 1b) 2c) 3d) 4
Q: b) 2 only
Answer: Fatty acid synthesis requires all of the following EXCEPT:1. ACP2. ADP3. NADPHa) 1 onlyb) 2 onlyc) 1 and 3 onlyd) 2 and 3 only
Q: d) unsaturated fatty acids
Answer: An inhibitor of isomerases in fatty acid oxidation would most hinder the catabolism of:a) terpenesb) saturated fatty acidsc) phospholipidsd) unsaturated fatty acids
Q: c) melting temperature
Answer: Increasing the amount of cholesterol in a plasma membrane would lead to an increase in:a) permeabilityb) atherosclerotic plaquesc) melting temperatured) freezing temperature
Q: c) 15 FADH2 & 31 NADH
Answer: Stearic acid is a 16-carbon saturated fatty acid. Including those made in the Krebs cycle, how many NADH and FADH2 would be produced by the complete oxidation of stearic acid?a) 15 FADH2 & 15 NADHb) 16 FADH2 & 16 NADHc) 15 FADH2 & 31 NADHd) 16 FADH2 & 32 NADH
Q: b) building an octamer of histones into a nucleosome using gyrase
Answer: Packing a eukaryotic genome involves all of the following structures or steps EXCEPT:a) wrapping linear portions of DNA around histone proteinsb) building an octamer of histones into a nucleosome using gyrasec) providing flexibility by leaving linker DNA between nucleosomes of approximately 80 base pairsd) condensing nucleosomes into chromatin
Q: d) it creates greater stability in the molecule
Answer: Why is the 2′ OH group removed from ribose in order to form the monosaccharide component of DNA?a) it ensures proper purine-purine pairingb) it converts a nucleoside into a nucleotidec) it sets up a phosphodiester bondd) it creates greater stability in the molecule
Q: a) pyrimidines hydrogen bond to purines, and a strand in its 5′ to 3′ orientation is paired with a strand in a 3′ to 5′ orientation
Answer: The DNA double helix is described as being both complementary and antiparallel. What characteristics of the polynucleotide generate these properties, respectively?a) pyrimidines hydrogen bond to purines, and a strand in its 5′ to 3′ orientation is paired with a strand in a 3′ to 5′ orientationb) the bases used on each strand are the same to facilitate hydrogen bonding, and a strand in its 5′ to 3′ orientation can pair with another strand in either the 5′ to 3′ or 3′ to 5′ orientationc) the greater the G-C content of a single DNA strand, the greater the degree of complementarity between strands, A-T content determines antiparallel orientationd) the number of base pairs per turn of helix establishes both
Q: a) acrocentric
Answer: Linked chromatids that are composed of extended q (long) arms with minimal p (short) arms would be best described as:a) acrocentricb) metacentricc) telocentricd) submetacentric
Q: c) G-C
Answer: Which DNA base pair requires the most energy to break?a) A-Tb) C-Ac) G-Cd) U-A
Q: b) it has a sequence containing introns and exons
Answer: What is the defining characteristic of heterogeneous nuclear RNA (hnRNA)?a) it has a methylated guanine cap on the 5′ endb) it has a sequence containing introns and exonsc) it contains uracild) it has a poly A sequence on the 3′ end
Q: b) to protect the ends of the chromosomes from damage due to incomplete replication
Answer: Telomeres are guanine-rich caps on the ends of each chromosome. Which of the following is the most likely function of a telomere?a) high guanine content stabilizes parental strands to prevent excess tension during DNA unwindingb) to protect the ends of the chromosomes from damage due to incomplete replicationc) to provide a site for helicase attachmentd) to seal the gaps left by Okazaki fragments in the lagging strand