CHEM 1005 Midterm Questions with 100% Verified Correct Answers Changes in the physiological variables listed below can alter the affinity of hemoglobin for oxygen.Which of the following will lower the affinity of hemoglobin for oxygen? - Correct Answer Increase in 2,3 bisphosphoglycerate (BPG) A decreased affinity will increase the rate of oxygen delivery to the tissues. This will occur when pH is low, there is an increase in CO2, protons or 2,3 BPG. The other scenarios (a, c, d) will all increase the affinity for O2.Which of the following proteins is likely to have quaternary structure? - Correct Answer A multimeric protein that contains multiple peptide chains Primary structure is the largely unfolded strand of amino acids, while β- sheets and α-helices are examples of secondary structures. How these structures interact would be an example of tertiary structure. Quaternary structure is a characteristic of interactions between several individual polypeptide chains.Chymotrypsin is a protease that cleaves peptide bonds. It is characterized as which of the following classes of enzymes? - Correct Answer Hydrolases Review the 6 classes of enzymes. Peptide bonds are cleaved and water is released in the reaction.How do most enzymes reduce the activation energy needed to move a reaction forward? - Correct Answer Providing an active site most complementary the transition state In the induced fit model, the active site is more homologous to the transition state of the reaction and this reduces the activation energy of the transition.An enzyme has a mutation within the substrate binding site that reduces the binding of the coenzyme needed for covalent catalysis. Which of the following is likely to result as a consequence of this mutation? - Correct Answer The enzyme will not be able to form the transition state complex Loss of coenzyme binding will result in inability to form the transition substrate enzyme complex. 1 / 3
α-helices and β-sheets are primarily stabilized by which of the following interactions? - Correct Answer Hydrogen bonding All secondary structures are stabilized through hydrogen bonding. The other forces participate in stabilizing tertiary and quaternary structures.Movement of ammonia from an amino acid to an α-keto acid involves a family of enzymes best categorized as which of the following? - Correct Answer Transferases Amino transferases are commonly used in the movement of ammonia and use the covalent catalysis "ping-pong method".An α-helical arrangement of amino acids is considered to be what level of protein structure? - Correct Answer Secondary structure of the protein β- sheets and α-helices are examples of secondary structures. How these structures interact would be an example of tertiary structure.A 28-year-old male is recently diagnosed with HIV. As part of his treatment he is prescribed Nevirapine which interferes with retroviral reverse transcriptase enzyme. Using the graph below, which of the following best describes the impact of this drug on its target? - Correct Answer It reduces the catalytic activity of the enzyme.There is no change in Km with the addition of the drug (as illustrated by the lines originating on X axis at the same point). There is a change in Vmax as illustrated by the divergence of the lines as they cross the X axis. This could be indicative of a noncompetitive inhibitor.The following represents a series of reactions. As levels of B increase, this will decrease the conversion of S3 to B. Which of the following best describes this type of regulation in a biosynthetic pathway? - Correct Answer Feedback inhibition Feedback inhibition in biosynthetic pathways can be simple or complex. The above example is a simple illustration of feedback inhibition. When levels of B increase this will negatively impact the production of B allowing substrate (S2) to be diverted A.Which of the following is an example of enzyme regulation through covalent modification? - Correct Answer Phosphorylation of muscle glycogen phosphorylase. 2 / 3
Phosphorylation is a common covalent modification that can have various impacts on activity.The association of DNA and histones can be modified by histone acetylation. A decrease in histone acetylation will have which of the following impacts on the association of DNA and histones? -
Correct Answer Increase DNA: histone association.
Histones can be modified by methylation, acetylation and ADP-ribosylation. Acetylation of histones decreases the positive charge on them and reduces the DNA:histone interaction. As the level of
acetylation decreases, the DNA:histone interactions will increase.
Which of the following best describes an enzyme inhibitor that increases the Km but does not change the Vmax? - Correct Answer A competitive inhibitor.This is the definition of a competitive inhibitor. The addition of a competitive inhibitor can be overcome by the addition of additional substrate therefore Vmax can be achieved but the affinity for the substrate is reduced.Use the figure below to compare the activities of glucokinase and hexokinase. Based on this information, which of the following is a true statement? - Correct Answer Glucokinase has a higher Km than hexokinase..As illustrated by the graph, hexokinase is able to reach Vmax at a much lower glucose concentration than glucokinase. Km is defined at ½ the substrate concentration needed to reach Vmax therefore if you compare the glucose concentration needed to reach Vmax in each case, glucokinase will have a much greater Km when compared to hexokinase.An example of enzyme activation by cleavage is best illustrated by which of the following? - Correct Answer Activation of chymotrypsinogen to chymotrypsin.Synthesis of enzymes as proenzymes is positive in the case of digestive enzymes such as chymotrypsin. This enzyme will only be active when cleaved under the required circumstances.An enzyme is participating in a general acid-base catalysis reaction with an optimal reaction pH of
6.0. If acid is added to the environment reducing the pH to 3, what is the likely impact to the rate of
reaction? - Correct Answer The rate of the reaction is likely to decrease as the pH is out of optimal catalytic range.
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