The transfer of a phosphate group to a molecule or organic compound is called phosphorylation. The process of phosphorylation occurs in regards to proteins, such as to stimulate or decrease an enzyme's function, as well as to assist in the movement of proteins to different areas of a cell.
When phosphorylation occurs, a phosphate group is added to a protein via its amino acid side chain. The addition of the phosphate greatly impacts the protein — it may change the charge of the protein and the shape, which ultimately affects its function. Additionally, phosphorylation is stimulated by enzymes that speed up the process of adding a phosphate group to an amino acid chain. For example, this commonly occurs when the enzymes known as kinases, catalyze the phosphorylation of adenonside triphosphate, or ATP, a high energy molecule needed to power a cell.
Phosphorylation is also responsible for the ability of proteins to bind to an amino acid. The process activates binding sites on a protein, from which phosphorylated amino acids are able to attach. Binding by phosphorylation is important to a cell's function, as it assist in movement, metabolism and reproduction. The process is also reversible and is known as dephosphorylation, in which the protein will revert back to its original state.