Question

Tertiary structure of a protein consisting of $\alpha$-helices and $\beta$-strands can be determined by:

• A. circular dichroism spectroscopy
• B. mass spectrometry
• C. nuclear magnetic resonance spectroscopy
• D. UV spectroscopy

Hint:

CD tells you "how much helix/sheet"; NMR tells you "how the whole protein folds in 3D".

Answer 1

The Correct Option is C

Tertiary structure describes the full 3D folding of a protein, including spatial arrangement of α-helices, β-strands, and loops. Determining this structure requires a method that can provide atomic-level information.

Step 1: Evaluate each technique.
- Circular dichroism (CD) spectroscopy provides secondary structure content (how much α-helix or β-sheet), but cannot resolve the 3D arrangement.
- Mass spectrometry identifies molecular mass and modifications, but not 3D folding.
- UV spectroscopy detects aromatic amino acids but provides no structural detail.
- Nuclear magnetic resonance (NMR) spectroscopy can determine the full tertiary structure of proteins in solution at atomic resolution.

Step 2: Conclusion.
Only NMR spectroscopy is capable of resolving the tertiary structure of proteins.