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5 Cards in this Set
- Front
- Back
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Which of the following describes a characteristic feature of an enzyme that obeys Michaelis-Menten kinetics? A. The enzyme velocity is at one-half the maximal rate when 100% of the enzyme molecules contain bound substrate. B. The enzyme velocity is at one-half the maximal rate when 50% of the enzyme molecules contain bound substrate. C. The enzyme velocity is at its maximal rate when 50% of the enzyme molecules contain bound s ubstrate. D. The enzyme velocity is at its maximal rate when all of the substrate molecules in solution are bound by the enzyme. E. The velocity of the reaction is independent of the concentration of enzyme. |
B. The enzyme velocity is at one-half the maximal rate when 50% of the enzyme molecules contain bound substrate.
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The pancreatic glucokinase of a patient with MODY had a mutation replacing a leucine with a proline. The result was that the Km for glucose was decreased from a normal value of 6 mM to a value of 2.2 mM, and the Vmax was changed from 93 U/mg protein to 0.2 U/mg protein. Which of the following best describes the patient’s glucokinase compared with the normal enzyme? A. The patient’s enzyme requires a lower concentration of glucose to reach ½Vmax. B. The patient’s enzyme is faster than the normal enzyme at concentrations of glucose 2.2 mM. C. The patient’s enzyme is faster than the normal enzyme at concentrations of glucose 2.2 mM. D. At near-saturating glucose concentration, the patient would need 90 to 100 times more enzyme than normal to achieve normal rates of glucose phosphorylation. E. As blood glucose levels increase after a meal from a fasting value of 5 mM to 10 mM, the rate of the patient’s enzyme will increase more than the rate of the normal enzyme. |
A. The patient’s enzyme requires a lower concentration of glucose to reach ½Vmax.
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Methanol (CH3OH) is converted by alcohol dehydrogenases to formaldehyde (CH2O), a compound that is highly toxic to humans. Patients who have ingested toxic levels of methanol are sometimes treated with ethanol (CH3CH2OH) to inhibit methanol oxidation by alcohol dehydrogenase. Which of the following statements provides the best rationale for this treatment? A. Ethanol is a structural analog of methanol and might therefore be an effective noncompetitive inhibitor. B. Ethanol is a structural analog of methanol that can be expected to compete with methanol for its binding site on the enzyme. C. Ethanol can be expected to alter the Vmax of alcohol dehydrogenase for the oxidation of methanol to formaldehyde. D. Ethanol is an effective inhibitor of methanol oxidation regardless of the concentration of m ethanol. E. Ethanol can be expected to inhibit the enzyme by binding to the formaldehyde-binding site on the enzyme, even though it cannot bind at the substratebinding site for methanol. |
B. Ethanol is a structural analog of methanol that can be expected to compete with methanol for its binding site on the enzyme.
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An allosteric enzyme has the following kinetic properties: a Vmax of 25 U/mg enzyme, and a Km,app of 1.0 mM. These kinetic parameters were then measured in the presence of an allosteric activator. Which one of the following would best describe the findings of that experiment? A. A Vmax of 25 U/mg enzyme, and a Km,app of 0.2 mM. B. A Vmax of 15 U/mg enzyme, with a Km,app of 2.0 mM. C. A Vmax of 25 U/mg enzyme, with a Km,app of 2.0 mM. D. A Vmax of 50 U/mg enzyme, with a Km,app of 5.0 mM. E. A Vmax of 50 U/mg enzyme, with a Km,app of 10.0 mM |
A. A Vmax of 25 U/mg enzyme, and a Km,app of 0.2 mM.
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A rate-limiting enzyme catalyzes the first step in the conversion of a toxic metabolite to a urinary excretion product. Which of the following mechanisms for regulat A. The product of the pathway should be an allosteric inhibitor of the rate-limiting enzyme. B. The product of the pathway should act through gene transcription to decrease synthesis of the enzyme. C. The toxin should act through gene transcription to increase synthesis of the enzyme. D. The enzyme should have a high Km for the toxin. E. The toxin allosterically activates the last enzyme in the pathway. |
C. The toxin should act through gene transcription to increase synthesis of the enzyme
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