Final answer:
Kinases are the enzymes that add a phosphate group to a switch protein, a process that is crucial in the regulation of cellular functions.
Step-by-step explanation:
The enzymes that add a phosphate group to a switch protein are called kinases. These enzymes facilitate the transfer of a phosphate group from ATP to specific amino acids in a protein, such as serine, threonine, or tyrosine, replacing their hydroxyl groups with a phosphate group (PO43-). This process, known as phosphorylation, often leads to a change in the protein's shape that can activate or deactivate its function. It is a critical mechanism in cellular signaling pathways that regulate various cellular processes. On the other hand, the enzymes that remove a phosphate group (dephosphorylation) are called phosphatases, G-proteins are involved in signal transduction but are not directly responsible for adding phosphate groups, and GTPases hydrolyze GTP to GDP and phosphate, involved in energy transfer and signal transduction but again not in phosphorylation of proteins.