MULTIPLE CHOICE
1. In regard to the expression of enzyme activity, a katal is:
a. a unit that describes the amount of substrate in moles converted to product in 1 minute.
b. a unit that describes the amount of enzy
...
MULTIPLE CHOICE
1. In regard to the expression of enzyme activity, a katal is:
a. a unit that describes the amount of substrate in moles converted to product in 1 minute.
b. a unit that describes the amount of enzyme that is consumed in 1 minute.
c. a unit that describes the amount of enzyme that will catalyze a mole of substrate in 1 second.
d. the substrate concentration at which the enzyme yields half the maximum velocity of the reaction.
2. When a coenzyme binds to an enzyme, the enzyme portion of the resulting molecule is referred to as the:
a. activator.
b. holoenzyme.
c. apoenzyme.
d. prosthetic group.
3. Which one of the following is a correct statement describing a property of an enzyme?
a. Enzyme activity is not altered by heat denaturation.
b. Enzymes affect the rate of a chemical reaction by being altered to fit into the active site of a substrate.
c. Enzymes are protein catalysts that decrease the activation energy of a chemical reaction.
d. Enzymes contain a site to which the product binds during an enzymatic reaction.
4. Statin drugs lower cholesterol by competitive inhibition of the cholesterol-synthesizing enzyme HMG-CoA reductase. A competitive inhibitor binds:
a. the enzyme at a site other than the active center, thereby decreasing the Vmax of the reaction.
b. to the active center of the enzyme, with no effect on the Vmax of the reaction.
c. to the entire enzyme-substrate complex, thereby decreasing the Km.
d. to the active center of the enzyme, thereby causing the Km to increase.
5. How does pH alter an enzymatic reaction rate?
a. By affecting key amino acids in the enzyme protein at the active center and other sites
b. By causing thermal inactivation through reconfiguration of the prosthetic group
c. By promoting the formation of the most active state of the enzyme
d. By decreasing the Km needed for maximum velocity to be reached
6. Regarding enzyme kinetics, the substrate concentration at which the reaction velocity is equal to 0.5 Vmax is referred to as:
a. Km.
b. Vmax association constant.
c. 1/.
d. first order concentration.
ANS: A
Km, the Michaelis-Menten constant, is the experimentally determined substrate concentration at which v = 0.5 Vmax.
DIF: 1 REF: Page 224-225 OBJ: 1 | 10
7. Zero-order kinetics occurs during the beginning of an enzyme-catalyzed reaction when a substrate concentration is high and the rate of the reaction is _____ on the _____ concentration.
a. dependent; substrate
b. dependent; coenzyme
c. independent; substrate
d. independent; enzyme
8. True isoenzymes, which are multiple forms of an enzyme that possesses the ability to catalyze an enzyme’s characteristic reaction, are formed by:
a. alteration of a carbohydrate side chain.
b. the existence of more than one gene locus coding for the structure of the enzyme protein.
c. association with other proteins and cofactors.
d. changes in the phosphorylation pattern of associated proteins.
9. During embryonic and fetal development, changes in isoenzyme distribution patterns are common. These changes are thought to result from:
a. mutation-driven gene expression that reoccurs in adult malignancies.
b. altered production due to a genetic defect.
c. increased production and secretion from all undifferentiated proliferating cells.
d. differential expression and changes in the relative activities of gene loci within developing cells.
10. Regarding enzyme kinetics, the Michaelis-Menten plot of the relationship between reaction velocity and substrate concentration is correctly expressed as which one of the following formulae?
a. = Vmax[S]/Km + [S]
b. = Km[S]/Vmax + [S]
c. = Vmax + [S]/Km[S]
d. = Km + [S]/Vmax[S]
11. Activators increase the rates of enzyme-catalyzed reactions. In some cases, these activators interact with the nonenzymatic component of the reaction such as the substrate. However, in most cases the activator:
a. acts as an uncompetitive inhibitor by binding to the product.
b. binds to the enzyme similar to the enzyme/substrate combination.
c. alters the enzyme’s chemical properties to produce an altered product.
d. destroys enzyme activity by denaturing the protein.
12. In a continuous-monitoring assessment of an enzyme reaction rate, which one of the following is the preferable measurement?
a. Measurement of the decreasing concentration of substrate
b. Measurement of the increasing concentration of product
c. Direct measurement of enzyme protein
d. Calculation of Km and Vmax
13. When determining the activity of an enzyme in serum as in a bisubstrate reaction, measurement of two different substances can be made. One measurement determines the decrease in substrate concentration acted upon by the enzyme and the other:
a. analyzes the disappearance of enzyme used in the reaction.
b. measures the increase in the concentration of a second substrate.
c. measures the increase in the concentration of the second product formed.
d. measures the amount of enzyme/substrate complex formed.
14. In the reciprocal plot pictured below, the solid line indicates a normal enzyme reaction with no inhibition, and the dotted line indicates a decrease in Vmax and no change in Km. This plot is an example of which type of inhibition?
a. Competitive
b. Noncompetitive
c. Uncompetitive
d. The type of inhibition cannot be determined with this information.
15. The reciprocal plot pictured below indicates a decrease in Vmax and a decrease in Km. The solid line indicates a normal enzymatic reaction. What type of enzymatic inhibition is this?
a. Competitive
b. Noncompetitive
c. Uncompetitive
d. The type of inhibition cannot be determined with this information.
16. Regarding measurement of a property related to substrate concentration such as fluorescence production, the assay that, although more technically demanding, theoretically provides the most accurate measurement of enzyme activity is the:
a. fixed-time assay.
b. equilibrium method.
c. discontinuous-monitoring assay.
d. two-point kinetic method.
17. An example of a posttranslational modification of an enzyme that produces an enzyme isoform would be:
a. association of different types of subunits in various combinations in an oligomer.
b. modification of genes at different loci.
c. alteration of carbohydrate side chains.
d. the existence of different allelic genes.
18. Immobilized enzymes are used analytically in various electrochemical techniques. The use of an ion-selective electrode that is coated with an enzyme that produces ions when placed in a substrate solution is a type of:
a. potentiometric measurement.
b. immunoassay.
c. equilibrium method.
d. consecutive enzymatic reaction.
19. Any condition, such as extreme temperature or extremes of pH, which changes the shape of the enzyme protein structure generally causes loss of enzymatic activity. This is referred to as:
a. activation.
b. inhibition.
c. denaturation.
d. optimization.
20. In regard to factors that govern the rate of an enzymatic reaction, first-order reaction kinetics occur at that part of the reaction during which the rate of the reaction is:
a. directly proportional to the substrate concentration.
b. proportional to the concentration of the enzyme present.
c. independent of either the enzyme or substrate concentration.
d. dependent upon the pH and temperature of the system.
21. The use of several enzymatic reactions linked together to provide a means of measuring the activity of the first enzyme or the concentration of the initial substrate is referred to as a(n):
a. equilibrium reaction.
b. consecutive enzymatic reaction.
c. self-indicating reaction.
d. enzyme immunoassay.
22. The interaction of the amino acid side chains with the arrangement of the -helices and -sheets to form a three-dimensional protein structure is called the _____ structure of the protein.
a. primary
b. secondary
c. tertiary
d. quaternary
23. All enzymes are classified to one of six classes based on the reaction they catalyze. Based on this classification, creatine kinase is a member of which one of the following enzyme classes?
a. Hydrolase
b. Oxidoreductase
c. Ligase
d. Transferase
24. Varying different factors and studying their effects on an enzymatic reaction rate in the assessment of most favorable reaction conditions for an enzyme assay is referred to as:
a. optimization.
b. standardization.
c. quality control.
d. variable control.
TRUE/FALSE
1. In an enzyme immunoassay such as ELISA, the specificity of the labeled enzyme is the most important aspect of the measurement.
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