Question

At what pH does poly-Glu in an aqueous solution form α-helical structure?

• A. 3
• B. 7
• C. 9
• D. 12

Hint:

When dealing with polypeptides, the structure can vary significantly with changes in pH. Neutral pH typically favors the α-helix structure in many proteins.

Answer 1

The Correct Option is A

Step 1: Understanding poly-Glu and its structure.
Poly-Glu, a polymer of glutamic acid, can adopt different secondary structures depending on the pH of the solution. At a neutral pH, poly-Glu typically forms an α-helical structure.
Step 2: Analyzing the options.
(A) 3: Incorrect — At pH 3, poly-Glu is likely to be in a different conformation, not α-helical.
(B) 7: Correct — Neutral pH (7) is the optimal condition for poly-Glu to form an α-helical structure.
(C) 9: Incorrect — At pH 9, poly-Glu may be in a different conformation due to deprotonation.
(D) 12: Incorrect — At pH 12, poly-Glu would likely be highly deprotonated and unable to form an α-helix.
Step 3: Conclusion.
The correct answer is (B) 7, as poly-Glu forms an α-helical structure most effectively at a neutral pH of 7.