Each amino acid consists of a central carbon atom (C) connected to a side chain (R), a hydrogen (H), a nitrogen-containing amino group (NH 2 ), and a carboxylic acid group (COOH) — hence the name “ami...Each amino acid consists of a central carbon atom (C) connected to a side chain (R), a hydrogen (H), a nitrogen-containing amino group (NH 2 ), and a carboxylic acid group (COOH) — hence the name “amino acid”. Amino acids differ from each other by which specific side chain (R) is bonded to the carbon center.