GATE 2023 BT – Question 28
Which one of the following methods CANNOT be used to determine the secondary structure content of a protein?
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Correct answer: (C) Mass spectrometry
Explanation
The question asks which method cannot give the **secondary structure content** (the fraction of helix, sheet and coil).
- **Circular dichroism:** the far-UV CD spectrum (190 to 250 nm) has characteristic shapes for $\alpha$-helix and $\beta$-sheet, so the fractions can be estimated. Usable.
- **FTIR spectroscopy:** the amide I band (about 1600 to 1700 cm⁻¹) depends on the secondary structure. Usable.
- **X-ray crystallography:** gives a full 3D structure, from which secondary structure is assigned. Usable.
- **Mass spectrometry:** measures mass-to-charge ratios, so it gives masses, sequences and modifications. It does not directly quantify the secondary structure. ✗
Answer **mass spectrometry** (C).