Haemoglobin is the textbook example of which level of protein structure?
Aprimary
Bsecondary
Ctertiary
Dquaternary
Answer & Solution
Correct answer: D. quaternary
Haemoglobin has four separate polypeptide chains (two α, two β) that come together to form the working molecule. That is the defining feature of quaternary structure. Primary is the sequence, secondary is local helices/sheets, tertiary is a single chain's 3D shape. Multi-chain assembly is the quaternary signature.
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