34. Following statements are made related to protein structure
    A. The hydrogen bonding patterns between the CO and NH groups are n → n +3 in α-helix; n → n + 4 in 3₁₀ helix and n → n + 5 in π helix.
    B. In a ß turn, there are 10 atoms between the hydrogen bond donor and acceptor.
    C. In a 𝛾 tum, there are 6 atoms between the hydrogen bond donor and acceptor.
    D. Parallel sheets have evenly spaced hydrogen bonds, which bridge the strands at an angle.

    Which one of the following combinations of above statements is correct?
    (1) A and C
    (2) A and B
    (3) C and D
    (4) B and D

Understanding Hydrogen Bonding Patterns in Protein Structures

Protein structures are stabilized by hydrogen bonding, which influences folding, stability, and function. Recognizing different hydrogen bonding patterns in helices, turns, and sheets is crucial for CSIR NET Life Science aspirants.

Correct Answer:

The correct option is (3) C and D.

Explanation:

(A) The hydrogen bonding patterns between CO and NH groups are n → n +3 in α-helix; n → n + 4 in 3₁₀ helix and n → n + 5 in π helix. ❌

• This statement contains an error in the description of hydrogen bonding in helices.
• Correct pattern:
  • α-Helix: n → n + 4 hydrogen bonding.
  • 3₁₀ Helix: n → n + 3 hydrogen bonding.
  • π-Helix: n → n + 5 hydrogen bonding.
• Since the pattern given for α-helix and 3₁₀ helix is incorrect, this statement is false.

(B) In a β-turn, there are 10 atoms between the hydrogen bond donor and acceptor. ❌

• A β-turn is a tight turn in protein structures where the carbonyl oxygen (CO) of residue n forms a hydrogen bond with the amide hydrogen (NH) of residue n+3.
• Correct fact: There are 9 atoms, not 10, between the hydrogen bond donor and acceptor.
• Therefore, this statement is false.

(C) In a γ-turn, there are 6 atoms between the hydrogen bond donor and acceptor. ✅

• γ-Turns are smaller than β-turns and involve a hydrogen bond between the n and n+2 residues.
• The number of atoms between the donor and acceptor is 6, making this statement true.

(D) Parallel β-sheets have evenly spaced hydrogen bonds, which bridge the strands at an angle. ✅

• In parallel β-sheets, hydrogen bonds form at an angle due to the alignment of peptide backbones.
• In contrast, antiparallel β-sheets have nearly perpendicular hydrogen bonds.
• Since this statement correctly describes parallel β-sheets, it is true.

Thus, the correct answer is (3) C and D.

Nearby Topics for Better Understanding

1. Hydrogen Bonding in Protein Secondary Structures

• Alpha-Helix: Stabilized by intra-chain n → n + 4 hydrogen bonds.
• Beta-Sheet: Stabilized by inter-chain hydrogen bonds, either parallel or antiparallel.
• Turns (β and γ): Play a role in sharp bends and compact folding.

2. Types of Helices in Proteins

3. Beta-Turn vs. Gamma-Turn

4. Importance of Beta-Sheets in Protein Folding

• Found in enzymes, antibodies, and structural proteins.
• Parallel sheets are less stable than antiparallel sheets due to angled hydrogen bonding.
• Contribute to protein aggregation diseases like Alzheimer’s (amyloid plaques).

Conclusion

Protein secondary structures, including helices, turns, and beta-sheets, rely on specific hydrogen bonding patterns. Understanding these patterns helps in predicting protein stability and function, a crucial aspect for CSIR NET Life Science aspirants.

By mastering these fundamental structural principles, students can confidently approach protein folding and stability questions in competitive exams.