Which of the following does not have a quaternary structure?
Which of the following does not have a quaternary structure?
Select an option to attempt
Correct Answer: Option D
Explanation
Quaternary structure = assembly of two or more polypeptide subunits (protomers) into a functional complex, stabilised by non-covalent interactions (hydrophobic, H-bonds, electrostatic) and sometimes disulfide bonds. Examples WITH quaternary structure: Haemoglobin (tetramer, 4 subunits); RNA Polymerase (multi-subunit complex:core in bacteria); Collagen (triple helix of 3-chains — counts as quaternary structure since 3 separate polypeptide chains). Myoglobin: a MONOMER (single polypeptide chain of 153 amino acids, MW ~17 kDa) — it has primary, secondary, and tertiary structure but NO quaternary structure (no subunit assembly). Myoglobin stores oxygen in muscle tissue; haemoglobin transports oxygen in blood.