Question

Self-assessment questions |107 4. What methods might be used to identify those parts of especially in the regulation of enzymes in metabolic pathways such as glycolysis. Usually, the amino acid that is phosphorylated is one of serine, threonine tyrosine or histidine. Explain why addition of a phosphate group to one of these amino acids can have a significant effect on the activity of a protein. a transmembrane protein that are exposed on the outer surface of the plasma membrane of an animal cell? 5. The MAP kinase cascade is an example ofa biochemical pathway in which phosphorylation is used to change the activity of a protein. Phosphorylation is also used to regulate protein activity in other contexts,
Number 5

Answer 1

5.

It changes the conformation and/or function of the molecule.

Phosphorylation is the addition of a phosphate group (PO₄³⁻) to a molecule, usually a protein. Phosphate has significant mass and charge, therefore it can change the folding (conformation) of the protein it attaches to.

Changing the conformation of a protein also affects it's function; most significantly in enzymes. When enzymes change conformation, their ability to bind their substrates alters. Phosphorylation can stimulate or inhibit the function of the molecule it attaches to and is therefore an essential control mechanism for the cell.

Such a conformational change is often stimulatory, but can also be inhibitory.