Protein Structure

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.

Step 1: Understanding disulfide bond formation.
Disulfide bonds are formed between pairs of cysteine residues. Given that there are six cysteines in the polypeptide, the number of possible disulfide pairings can be calculated using combinations. The number of ways to choose 2 cysteines from 6 is given by the combination formula: where .
Step 2: Calculating the number of combinations.

Step 3: Conclusion.
The number of different disulfide combinations possible is 15.

Step 1: Understanding the relationship.
The absorption of light by a solution follows Beer's Law, which states that absorption is directly proportional to the concentration. Since absorption increases with concentration, the transmitted light decreases proportionally.
Step 2: Calculation.
At a concentration of 0.1%, 20% of light is absorbed, meaning 80% is transmitted. If the concentration increases to 0.4%, absorption will increase proportionally. The fraction of light transmitted can be calculated using the relationship between absorption and concentration. The transmitted fraction at 0.4% will be 10%.
Step 3: Conclusion.
The fraction of light transmitted is 0.10.