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[1] [2] A polypeptide is a longer, continuous, unbranched peptide chain. [3] Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. [4] Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
Peptide bond formation via dehydration reaction. When two amino acids form a dipeptide through a peptide bond, [1] it is a type of condensation reaction. [2] In this kind of condensation, two amino acids approach each other, with the non-side chain (C1) carboxylic acid moiety of one coming near the non-side chain (N2) amino moiety of the other.
Protein complexes are distinct from multidomain enzymes, in which multiple catalytic domains are found in a single polypeptide chain. [1] Protein complexes are a form of quaternary structure. Proteins in a protein complex are linked by non-covalent protein–protein interactions. These complexes are a cornerstone of many (if not most ...
A β-elimination reaction also splits the chain, but results in a pyruvoyl group at the new N-terminus. This pyruvoyl group may be used as a covalently attached catalytic cofactor in some enzymes, especially decarboxylases such as S-adenosylmethionine decarboxylase (SAMDC) that exploit the electron-withdrawing power of the pyruvoyl group.
Limited proteolysis of a polypeptide during or after translation in protein synthesis often occurs for many proteins. This may involve removal of the N-terminal methionine, signal peptide, and/or the conversion of an inactive or non-functional protein to an active one.
Another method of termination is the reaction between a lipid radical and a lipid peroxide, or the combination of two lipid peroxide molecules, resulting in stable nonreactive molecules. [ 4 ] [ 5 ] Reinforced lipids that become part of the membrane if consumed with heavy isotope diet also inhibit peroxidation.
Once synthesis of the polypeptide chain is complete, the polypeptide chain folds to adopt a specific structure which enables the protein to carry out its functions. The basic form of protein structure is known as the primary structure, which is simply the polypeptide chain i.e. a sequence of covalently bonded amino acids. The primary structure ...
Permanent side-chain protecting groups used during Boc/benzyl SPPS are typically benzyl or benzyl-based groups. [1] Final removal of the peptide from the solid support occurs simultaneously with side chain deprotection using anhydrous hydrogen fluoride via hydrolytic cleavage. The final product is a fluoride salt which is relatively easy to ...