Final answer:
The function of a protein kinase is to phosphorylate proteins, which can activate or inactivate them, depending on the protein and the context within the cell. This action is essential for regulating various cellular processes including metabolism, gene expression, and signal transduction.
Step-by-step explanation:
The function of a protein kinase is to transfer phosphate groups from ATP (adenosine triphosphate) to specific proteins, a process known as phosphorylation. This modification can change the protein's function by altering its shape or charge, often resulting in activation or inactivation, depending on the context within the cell's signaling pathways. For example, cyclic AMP (cAMP) activates a type of protein kinase known as cAMP-dependent kinase, which in turn phosphorylates various target proteins influencing cellular metabolism, gene transcription, and other critical processes.
A specific instance of protein kinase action involves Protein Kinase C (PKC), which is activated by diacyl glycerol (DAG) and Calcium ions (Ca2+). PKC then phosphorylates serine and threonine residues on certain proteins within the cell, affecting their activity. This process can regulate a multitude of cellular functions, such as changes in metabolism, gene expression, and cellular communication.