quaternary structure of a protein

• Some proteins are made of several different polypeptide chains held together by bonds. The quaternary structure is the way these polypeptide chains are assembled together.
• Haemoglobin is made of four polypeptide chains, bonded together
• The quaternary structure tends to be determined by the tertiary structure of the individual polypeptide chains being bonded together. For proteins made from more than one polypeptide chain, the quaternary structure is the protein's final 3D structure.