This section covers amino acids as protein monomers, their general structure and their variable R groups.
Amino acids are monomers that join together to build proteins.
The 20 amino acids common in living organisms share the same basic arrangement. Each has a central carbon bonded to:
an amine group, −NHX2
a carboxyl group, −COOH
a hydrogen atom
an R group, or side chain
It is the R group that changes between these amino acids, giving different amino acids different properties.
Recognising an amino acid
An unfamiliar amino acid can be recognised by its common structural features: a central carbon carrying an amine group, a carboxyl group, a hydrogen atom and an R group. The R group itself can vary considerably.
Exam Tip: When identifying an amino acid from a structural formula, refer specifically to the amine and carboxyl groups. Do not use the appearance of the R group as the deciding feature.