AP BIOLOGY

Detailed explanation-1: -Many proteins in the cell are regulated by phosphorylation, the addition of a phosphate group. A family of enzymes called kinases adds phosphate groups to a protein substrate. Kinases phosphorylate their targets by transferring the terminal phosphate group of ATP (or GTP) to its substrate.

Detailed explanation-2: -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-3: -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-4: -The addition of a phosphate (PO43-) molecule to a non-polar R group of an amino acid residue can turn a hydrophobic portion of a protein into a polar and extremely hydrophilic portion of a molecule.

Detailed explanation-5: -Phosphorylation regulates protein function and cell signaling by causing conformational changes in the phosphorylated protein. These changes can affect the protein in two ways. First, conformational changes regulate the catalytic activity of the protein.