Paper 2 · proteins and haemoglobin
A haemoglobin molecule is made up of four polypeptide subunits, two alpha chains and two beta chains, held together as a single functional unit. What level of protein structural organisation does this represent?
Model answer
quaternary structure
Also accepted: the quaternary structure, quaternary
Explanation: Quaternary structure describes a protein built from two or more separate polypeptide chains (subunits) assembled together into one functional molecule; haemoglobin's four chains held together by hydrogen bonds, ionic bonds and hydrophobic interactions is a classic example.
Derived from ZIMSEC Biology Paper 2, November 2004, Q6
