Amino acids are organic molecules that have at least two functional groups. The diagram below is the ball and stick model for a generic amino acid:
Amino acids have two functional groups:
There are around 20 standard amino acids, and while they all have variations in their side chains, they share the same basic structure with an amino group and a carboxylic acid group. Amino acids are polymerised in cells to form peptides, which can fold into complex shapes or combine with other peptides to form proteins.
As amino acids have two functional groups, they can react to form a condensation polymer. For example, the two glycine molecules can react to form poly(glycine) and a molecule of water. This reaction is called condensation polymerisation.
As the amino acids in this polymer are linked by peptide bonds, it is a polypeptide. We can continue to add more glycine molecules to form a longer polypeptide chain.