The quaternary structure of a protein is the fourth level of organisation. It refers to the arrangement of cross-linked proteins (several polypeptide chains inter-linked). The structure is held together by hydrogen bonds, disulphide bonds, ionic bonds and hydrophobic interactions .
The simplest form is when two polypeptide chains (2 subunits) form a dimer, a more complicated example is that of haemoglobin. Haemoglobin has 4 subunits which interact to form the quaternary structure. Small changes to this allow it to carry oxygen round the body to organs.
- ↑ Biology 1 for OCR, Mary Jones, Cambridge University Press (2008)