Amino acids are molecules that have two different functional groups: an amino group (-NH2) and a carboxylic acid group (-COOH). Glycine is the simplest amino acid and its formula is H2NCH2COOH.
Amino acids react by condensation polymerisation to produce polypeptides. The amino group of one molecule reacts with the carboxylic acid group of the next, and a molecule of water is lost each time. Two amino acids joined together lose one water molecule. Because each amino acid has both types of group, a single amino acid such as glycine can polymerise on its own.
Different amino acids can be combined in the same chain. This produces proteins. The order of the different amino acids in the chain decides which protein is made.