GATE 2021 BT – Question 44

Recombinant DNA Technology and Other Tools in Biotechnology · Analytical tools: Microscopy and spectroscopy · 2 marks · Multiple choice

Tertiary structure of a protein with α-helices and β-strands can be determined by

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Correct answer: (C) nuclear magnetic resonance spectroscopy

Explanation

The question asks for a method that gives the **tertiary** (three-dimensional) structure.

**Circular dichroism:** estimates the fraction of $\alpha$-helix and $\beta$-sheet (secondary structure), not the 3D fold. ✗
**Mass spectrometry:** gives the mass and sequence information. ✗
**Nuclear magnetic resonance (NMR):** measures distance restraints between atoms (NOEs) and angles, from which a full 3D structure of a protein in solution can be calculated. ✓
**UV spectroscopy:** gives only the absorbance of aromatic residues and peptide bonds. ✗

(X-ray crystallography is the other main method, but it is not among the options.) Answer **NMR** (C).