The phosphorylation of proteins by ATP
A) is catalyzed by enzymes known as "protein kinases."
B) always stimulates the activity of an enzyme.
C) is catalyzed by adenyl cyclase.
D) always takes place in the cytoplasm.
E) is catalyzed by G proteins.

Question

Quizplus · Accepted Answer

The process of phosphorylation, in which a phosphate group is added to a protein molecule, is catalyzed by enzymes known as protein kinases.

Answer: B
 The effect of phosphorylation on protein activity is context-dependent and can either stimulate or inhibit enzyme activity, depending on the specific protein and the location of the phosphorylation site.

Answer: C, D, and E are incorrect
 Adenyl cyclase is not involved in protein phosphorylation, and the process can occur in various cellular compartments, not just the cytoplasm. G proteins also do not catalyze protein phosphorylation, although they can play a role in activating or inhibiting protein kinases.

The Phosphorylation of Proteins by ATP