GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Help with Other Regulatory Mechanisms
How is pepsinogen activated in the stomach?
A portion is cleaved, activating the enzyme
It is phosphorylated by another enzyme
It is activated by the temperature change in the stomach lumen
Cofactors bind to the enzyme, increasing its efficiency
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.
How does a noncomeptitive inhibitor affect an enzyme?
Lowers the maximum rate of the enzymatic reaction
Raises the maximum rate of the enzymatic reaction
Raises the Michaelis constant of the enzyme
Lowers the Michaelis constant of the enzyme
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.
How do competitive inhibitors affect enzyme efficiency?
Raise the Michaelis constant
Lower the Michaelis constant
Raise the maximum rate of the enzymatic reaction
Lower the maximum rate of the enzymatic reaction
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.