10. Which one of the following statements on protein conformation is NOT true?
    (1) Dihedral angles of side-chains in amino acids are depicted in the Ramachandran plot.
    (2) Infrared spectroscopy can be used to deduce hydrogen bonding in peptides.
    (3) Three dimensional structures of protein composed of 100 amino acids can be obtained by nuclear magnetic resonance spectroscopy
    (4) Globular proteins have α-helical and ß- sheet components

Understanding Protein Conformation: Key Facts and Misconceptions

Proteins adopt specific conformations that determine their function. Various techniques like Ramachandran plots, infrared spectroscopy, and NMR help analyze these structures. However, not all commonly believed facts are correct.

Correct Answer:

The incorrect statement is:

(1) Dihedral angles of side-chains in amino acids are depicted in the Ramachandran plot.

Explanation of the Answer Choices

1. The Ramachandran Plot Does NOT Show Side-Chain Dihedral Angles (Incorrect Statement)

• The Ramachandran plot only depicts the φ (phi) and Ψ (psi) backbone dihedral angles of amino acid residues.
• It does not show the side-chain (χ, chi) angles, which are analyzed using a rotamer plot.

2. Infrared Spectroscopy Identifies Hydrogen Bonding (Correct Statement)

• Infrared (IR) spectroscopy measures bond vibrations.
• Hydrogen bonds shift absorption peaks, helping identify α-helices, β-sheets, and random coils.

3. NMR Can Determine Protein Structures of ~100 Amino Acids (Correct Statement)

• Nuclear Magnetic Resonance (NMR) spectroscopy determines 3D structures of small to medium proteins (≤100-150 residues).
• Larger proteins require X-ray crystallography or cryo-EM.

4. Globular Proteins Contain Both α-Helices and β-Sheets (Correct Statement)

• Most globular proteins have both α-helices and β-sheets, allowing compact folding.
• Examples include hemoglobin and myoglobin.

Significance of Protein Conformation Analysis

1. Understanding Protein Folding Disorders

• Misfolded proteins cause diseases like Alzheimer’s and Parkinson’s.

2. Drug Discovery and Design

• Structural knowledge helps in designing target-specific drugs.

3. Engineering Synthetic Proteins

• Protein conformation guides bioengineering applications.

Conclusion

While IR spectroscopy, NMR, and globular protein structures are correctly described, the Ramachandran plot does not depict side-chain dihedral angles. This common misconception highlights the importance of understanding protein analysis techniques correctly.