Quaternary structure

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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 [1]. The quaternary structure is the final protein structure.

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 [2].


  1. Biology 1 for OCR, Mary Jones, Cambridge University Press (2008)
  2. Berg JM, Tymoczko JL, Stryer L. (2002) Biochemistry. 5th edition, New York: W H Freeman. Online version used, available at http://www.ncbi.nlm.nih.gov/books/NBK22550/

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