Whether or not an enzyme is present and active within a cell depends on

A) if the gene for the enzyme has been turned on and the enzyme made.
B) if the enzyme has been activated or inactivated.
C) whether an inhibitor is bound to the enzyme.
D) whether the necessary cofactor is present.
E) All of the answer choices could affect enzyme activity.

All of the listed factors can affect enzyme activity. The presence or absence of the enzyme itself is determined by whether the gene for the enzyme has been turned on and the enzyme synthesized. Once the enzyme is present, it may require activation (or inactivation) before it can function. Additionally, an inhibitor molecule may bind to the enzyme and prevent it from working, or a necessary cofactor may be absent and prevent the enzyme from catalyzing its reaction.