The vast array of metabolic reactions do not all occur in the cell at the same rate. Metabolic reactions can be regulated through control of the activities of the enzymes that catalyze these reactions. An important type of regulation of enzyme activity is feedback inhibition, in which the final product of a biosynthetic pathway feeds back and inhibits the first enzyme unique to that pathway.
Covalent modification is a regulatory mechanism for temporarily inactivating a specific enzyme.
Section 7.3 Positive regulators of transcription are called activator proteins. They bind to activator binding sites on the DNA and stimulate transcription by RNA polymerase. Activator protein activity, like repressor protein activity, is modified by effectors. For positive control of enzyme induction, the effector promotes the binding of the activator protein and thus stimulates mRNA synthesis. Compare and contrast the activities of an activator protein and a repressor protein.