# DBT JRF 2020 — Question 131

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Easy

## Question

Which of the following does not have a quaternary structure?

## Options

- **A.** haemoglobin
- **B.** RNA polymerase
- **C.** collagen
- **D.** myoglobin

## 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 ( $\alpha_2\beta_2$ tetramer, 4 subunits); RNA Polymerase (multi-subunit complex: $\alpha_2\beta\beta'\omega$ core in bacteria); Collagen (triple helix of 3 $\alpha$ -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.

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