· The polypeptide chain of a protein rarely forms a disordered structure (random coil) as proteins generally have functions to fulfil, and these functions rely upon specificity.
· In turn, functionality requires a definite 3D structure or conformation of the polypeptide chain.
· Proteins generally possess a degree of flexibility necessary for function e.g. muscle fibres
1. Give examples of the post translation modifications of amino acids, with reference to glycosylation, hydroxylation and carboxylation.
· Even after synthesis, (post translation), the starting set of 20 amino acids can be modified to create novel amino acids, enhancing the capabilities of the protein.
· Proline can be modified to produce hydroxyproline e.g. collagen fibres, a major constituent of skin, cartilage, teeth & bones.
· These additional hydroxyl groups help to stabilise the fibres.
· The addition of sugar residues to the asparagine residues of proteins (N-linked glycosylation) increases their solubility and also protects them from enzymatic degradation.
· Deficiency of N-linked sugar chain transfer is detected in congenital carbohydrate-deficient glycoprotein (CGD) syndrome which affects multiple tissues and has life threatening complications.
· Similarly, g-carboxyglutamate is produced by the carboxylation of glutamate.
· The formation of g-carboxyglutamate residues within several proteins of the blood clotting cascade (e.g. factor IX) is critical for their normal function by increasing their calcium binding capabilities.
The anticoagulant warfarin works by inhibiting the carboxylation reaction