AP BIOLOGY

Detailed explanation-1: -The protein kinases belong to the great family of kinases and are responsible for the mechanism of phosphorylation. They are activated by phosphorylation which in turn activates a cascade of events leading to the phosphorylation of different amino acids (3).

Detailed explanation-2: -Protein kinases (PTKs) are enzymes that regulate the biological activity of proteins by phosphorylation of specific amino acids with ATP as the source of phosphate, thereby inducing a conformational change from an inactive to an active form of the protein.

Detailed explanation-3: -In many cases, the enzyme being phosphorylated is itself a kinase. The classical example is that protein kinase A phosphorylates the enzyme phosphorylase kinase, which, in turn, phosphorylates glycogen phorphorylase, which leads to breakdown of glycogen in liver and muscle.

Detailed explanation-4: -Protein kinases and phosphatases are enzymes catalysing the transfer of phosphate between their substrates. A protein kinase catalyses the transfer of -phosphate from ATP (or GTP) to its protein substrates while a protein phosphatase catalyses the transfer of the phosphate from a phosphoprotein to a water molecule.

Detailed explanation-5: -The role of a protein kinase is to transfer the -phosphate of magnesium adenosine triphosphate (MgATP) to other proteins. PKA phosphorylates serine and threonine residues; the tyrosine hydroxyl group is phosphorylated by a different enzyme.