Question

How does a phosphorylation cascade work? What does it do to the original signal?

Answer 1

The attachment of the phosphoryl group to any molecule is called its phosphorylation. The cascade is a sequence of amplification chain reactions where the product of one reaction activates the reactant of the next reaction. The activated enzyme inactivates the inactivated enzyme, and so on.

Complete answer:
Phosphorylation is the biochemical process that occurs by the addition of the phosphoryl group to the organic compound. Its reverse process is dephosphorylation. These two processes are extensively used in many biological mechanisms. It occurs at the site of damaged DNA and in various metabolic and signaling pathways.

A phosphorylation cascade is used for the transduction or transmission of signals. It has three major steps- reception, transduction, and response. It is a sequence of reactions that results in the phosphorylation of different proteins. One enzyme phosphorylates the other in this chain reaction. The transmission of messages of hormones follows this process. The hormone binds to the receptor molecule present on the extracellular matrix of the cell surface. This binding causes a conformational change in the receptor molecule. This causes the activation of the receptor molecule by the addition of the phosphoryl group. The activated receptors trigger the initiation or activation of other secondary messengers or proteins by adding the phosphoryl group to them. These activated messengers will activate thousands of proteins that remain in this state for a longer time. They connect the cell surface to the nucleus through this cascade mechanism. The result is the gene expression in the cell or changes occurring in the cells during the cascade.

Kinases are the class of enzymes that follow this process. This cascade mechanism amplifies the original signal received by the cell surface many times by activating the protein molecules and the secondary messengers in the cell. They remain in the active stage for a longer time and thus can process more molecules. At each step, the number of activated molecules increases by many folds and thus producing a larger cellular response with few signaling molecules. So, by this process, the pathway amplifies the original signal and thus leads to the activation of many target molecules by one ligand or receptor. It also improves the signal.
An important example of this pathway is the Mitogen-Activated Protein Kinase. They use the enzyme kinase and help in cellular growth and cell division.

Note: Phosphorylation cascade plays other significant features as well. It integrates the multiple signal inputs into a single output. The kinase and phosphatases mediate an on/off switch that provides reversibility. The hyperactivity or malfunction of this process can also lead to various diseases like cancer or the development of tumors.