1. Proteins and peptides

1.1 Composition and structure

Proteins are polypeptides, or unbranched polymers of amino acids. Amino acids carry two chemical functions: amine and carboxylic acid (figure 1 ). There are twenty naturally occurring amino acids, differentiated by the chemical groups R in their side chains, which give them their physico-chemical properties. The heavy atoms within the side chains are "numbered" in the order of the Greek alphabet, the α-carbon being the aliphatic carbon onto which the side chain grafts. Hydrogens are "numbered" according to the heavy atom to which they are bonded.

The twenty amino acids carry different types of side chains: uncharged aliphatic side chains,...