Amino Acids

An amino acid contains both an amine group, -NH₂, and a carboxylic acid group, -COOH. The amino acids found in proteins are α-amino acids: both groups are attached to the same carbon atom. Their general formula is:RCH(NH₂)COOHR is the side chain, which is different for each amino acid. For example:
• glycine: R = H
• alanine: R = CH₃
• serine: R = CH₂OH
• cysteine: R = CH₂SH
Side chains can be non-polar, polar, acidic (with an extra -COOH) or basic (with an extra -NH₂).Naming. Amino acids have common names, but you should be able to give IUPAC names. The COOH carbon is C1. Alanine, CH₃CH(NH₂)COOH, is 2-aminopropanoic acid; glycine is aminoethanoic acid.Chirality. In every amino acid except glycine, the central carbon is bonded to four different groups (H, NH₂, COOH and R). It is a chiral centre, so the amino acid exists as two optical isomers (enantiomers). Glycine has two H atoms on this carbon, so it is not chiral.Worked example. Name valine, (CH₃)₂CHCH(NH₂)COOH. The longest chain including the COOH carbon has four carbons, with NH₂ on C2 and a methyl group on C3: 2-amino-3-methylbutanoic acid.