Protein backbone
A peptide bond (amide bond) is a covalent chemical bond linking two consecutive amino acid monomers along a peptide or protein chain.
When two amino acids form a dipeptide through a peptide bond it is called condensation. In condensation, two amino acids approach each other, with the acid moiety of one coming near the amino moiety of the other. One loses a hydrogen and oxygen from its carboxyl group (COOH) and the other loses a hydrogen from its amino group (NH2). This reaction produces a molecule of water (H2O) and two amino acids joined by a peptide bond (-CO-NH-). The two joined amino acids are called a dipeptide.
The peptide bond is synthesized when the carboxyl group of one amino acid molecule reacts with the amino group of the other amino acid molecule, causing the release of a molecule of water (H2O), hence the process is a dehydration synthesis reaction (also known as a condensation reaction).
The formation of the peptide bond consumes energy, which, in living systems, is derived from ATP.Polypeptides and proteins are chains of amino acids held together by peptide bonds. Living organisms employ enzymes to produce polypeptides, and ribosomes to produce proteins. Peptides are synthesized by specific enzymes. For example, the tripeptide glutathione is synthesized in two steps from free amino acids, by two enzymes: gamma-glutamylcysteine synthetase and glutathione synthetase.
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