Briefly discuss two mechanisms of post-translation modification of protein synthesis.

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Most of the newly synthesized proteins are not functional. After attaining a three dimensional structure by folding mechanism, these proteins undergo several structural and chemical alterations to become fully functional. This changes include additions, deletions, trimming and structural reorganization. All the changes that are needed by the newly synthesized proteins after completion of translation are known as post translational modifications.

Trimming:- many proteins are originally synthesized as much bigger molecules. During trimming, the proteins get rid of the unwanted portion of the original precursor molecule by proteolysis and release the active protein. There are several examples- formation of insulin from preproinsulin, zymogens to active enzymes, etc.
Structural reorganization:- compared to the introns of mRNA, there are certain intervening portions in proteins called inteins which are removed during post translational processing. The remaining exteins are spliced together to form the functional protein molecule.
Modifications at the N-terminal and C-terminal ends:- the N-terminal of the polypeptide contains formylmethionine (prokaryotes) and methionine (eukaryotes). In most cases the amino acids at the amino terminal and carboxy terminal ends are either removed or modified during post translational modifications.
Covalent modifications:- Phosphorylation:- the enzymes that add phosphate group are called protein kinases, while those that remove phosphate group are called protein phosphatases. The regulatory enzymes of major metabolic pathways are subject to alternate phosphorylation dephosphorylation depending on the cellular needs. Hydroxylation:- In collagen, amino acids proline and lysine are hydroxylated to form hydroxyproline and hydroxylysine respectively. This post translational modification make the collagen mature. The hydroxylation of amino acids is useful in forming covalent crosslinks that confer rigidity on the triple helical structure of the collagen molecule. Glycosylation:- many proteins contain extensive carbohydrate side chains (glycoproteins). These oligosaccharide side chains are usually attached to the hydroxyl groups of serine and threonine (O-linked glycoproteins) or to the amino group of asparagine (N-linked glycoproteins).

gladiator answered 1 year ago

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