Question

Answer ALL questions please. ALL QUESTIONS

1) Protein kinase A (PKA) is a family of enzymes that are part of cell signal systems, and their effect is to phosphorylate proteins, altering their activity. As an example, PKA can phosphorylate the enzyme acetyl- CoA carboxylase, causing it to activate. The ?G for this phosphorylation is +4.2 kcal/mol. How is ATP used to phosphorylate this enzyme, and how does phosphorylation affect enzyme activity?

Answer 1

Protein kinase A is a protein that is dependent on cyclic AMP and is deactivated without it. When cAMP binds to a regulatory subunit, a conformational change occurs. This mens that catalytic subunit becomes active and is no longer inhibited. The protein can now phosphorylate other proteins by removing a phosphate from ATP, and adding it to a serine or threonine residue on the target protein which in turn leads to cellular response. ATP supplies the phosphate for the phosphorylation.

The phosphorylation results in changes in activity of substrate. In case of direct protein phosphorylation, PKA either increases or decreases enzymatic activity. In case of protein synthesis, it alters transcription and therefore synthesis of proteins.