What is the significance of phosphorylation?

Phosphorylation has crucial roles in the regulation of different cellular processes such as cell cycle, apoptosis, growth, and signal transduction pathways. Phosphorylation regulates protein function by inducing conformational alterations in phosphorylated proteins, leading to their activation or inactivation. Thus, phosphorylation may modulate enzymatic activity, and influence protein localization within cells by adding or removing phosphate groups. During signal transduction, phosphorylation acts as a molecular switch which transmits signals from the cell surface to the intracellular components. Activation of cell surface receptors generates a cascade of phosphorylation events, which induces the signal through a series of phosphorylation-dependent protein-protein interactions. Phosphorylation has a significant role in the regulation of the cell cycle, controlling transition between different phases and ensuring proper cell division. Phosphorylation of specific proteins during the cell cycle regulates DNA replication, and chromosome segregation. Gene expression can also be modulated by phosphorylation, by influencing the activity of transcription factors. Phosphorylation can regulate DNA-binding affinity, and thus affect their ability to activate or repress target genes.