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In molecular biology, post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes , which translate mRNA into polypeptide chains , which may then change to form the mature protein product.
Protein phosphorylation is a reversible post-translational modification of proteins. In eukaryotes, protein phosphorylation functions in cell signaling, gene expression, and differentiation. It is also involved in DNA replication during the cell cycle, and the mechanisms that cope with stress-induced replication blocks.
Histone post-translational modifications modify the chromatin structure. The most commonly associated histone phosphorylation occurs during cellular responses to DNA damage, when phosphorylated histone H2A separates large chromatin domains around the site of DNA breakage. [6]
Post-translational modifications can incorporate more complex, large molecules into the folded protein structure. One common example of this is glycosylation, the addition of a polysaccharide molecule, which is widely considered to be most common post-translational modification. [16]
Transcriptional modification or co-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene to produce a mature, functional RNA molecule that can then leave the nucleus and perform any of a variety of different functions in the cell. [1]
Protein phosphorylation is the most abundant post-translational modification in eukaryotes. Phosphorylation can occur on serine , threonine and tyrosine side chains (in other words, on their residues) through phosphoester bond formation, on histidine , lysine and arginine through phosphoramidate bonds , and on aspartic acid and glutamic acid ...
Acetylation is an important modification of proteins in cell biology; and proteomics studies have identified thousands of acetylated mammalian proteins. [1] [2] [3] Acetylation occurs as a co-translational and post-translational modification of proteins, for example, histones, p53, and tubulins.
O-glycosylation is a post-translational modification that occurs after the protein has been synthesised. In eukaryotes , it occurs in the endoplasmic reticulum , Golgi apparatus and occasionally in the cytoplasm ; in prokaryotes , it occurs in the cytoplasm. [ 1 ]