Amino acid side chains stabilise the enzyme

shape

Hydrogen bonds in the tertiary protein structure

Many amino acids contain groups in the side chains that have a hydrogen atom attached to either an oxygen or nitrogen atom. Hydrogen bonding can occur between such groups.

Ionic bonds in the tertiary protein structure

An ionic bond can form between amino acids which contain a carboxylic acid group (-COOH) and an amino group (-NH2)

Sulfur BridgesAnother way in which the tertiary structure can be held in place involve the amino acid cysteine. A sulfur bridge is a type of bond that can form between two cysteine residues that are close together when the protein chain is folded. Each cysteine residue loses a hydrogen in the form of H+. This is a covalent bond between the two sulphur atoms (S-S) which is stronger than a hydrogen bond.