GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Enzymes
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #21 : Enzymes
You have an enzyme solution and you add an inhibitor molecule and observe a marked decrease in enzyme activity. You increase the substrate concentration but this does not lead to any observable increase in enzyme activity. What can you conclude about your inhibitor?
That it binds the enzyme's active site
That is it an inorganic inhibitor
That it is a competitive inhibitor
That it is a noncompetitive inhibitor
That it is a kinase
That it is a noncompetitive inhibitor
Noncompetitive inhibitors bind to enzymes away from the active site (allosteric) and distort it, reducing its affinity for substrate. Since they do not directly compete with substrate for enzyme binding, increasing the substrate concentration in the presence of a noncompetitive inhibitor will have no affect. While enzyme inhibitors include both organic and inorganic molecules, there is not enough information in the question stem to conclude the chemical classification of the inhibitor.
Example Question #1 : Help With Other Regulatory Mechanisms
How do competitive inhibitors affect enzyme efficiency?
Lower the maximum rate of the enzymatic reaction
Raise the maximum rate of the enzymatic reaction
Lower the Michaelis constant
Raise the Michaelis constant
Raise the Michaelis constant
Competitive inhibitors can be overpowered by introducing excess substrate, so they do not affect the maximum rate of the enzyme. They do, however, make it so that more substrate is required in order to get the enzyme working at half of its maximum rate. As a result, competitive inhibitors act by raising the Michaelis constant of enzymes.
Example Question #2 : Help With Other Regulatory Mechanisms
How does a noncomeptitive inhibitor affect an enzyme?
Lowers the Michaelis constant of the enzyme
Raises the maximum rate of the enzymatic reaction
Raises the Michaelis constant of the enzyme
Lowers the maximum rate of the enzymatic reaction
Lowers the maximum rate of the enzymatic reaction
A noncompetitive inhibitor acts to decrease how fast the enzyme can act on substrates. It accomplishes this by lowering the maximum rate at which it can create products. Noncompetitive inhibitors do not alter the enzyme's Michaelis constant.
Example Question #64 : Biochemistry
How is pepsinogen activated in the stomach?
It is activated by the temperature change in the stomach lumen
It is phosphorylated by another enzyme
Cofactors bind to the enzyme, increasing its efficiency
A portion is cleaved, activating the enzyme
A portion is cleaved, activating the enzyme
Once in the stomach lumen, pepsinogen finds itself in a very acidic environment. The acidic environment cleaves an amino acid sequence from pepsinogen, turning it into the active enzyme pepsin. This type of activation causes pepsin to only activate in the stomach lumen where it is needed.
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