Question

which of the following best describes the effect of a greater number of cysteine amino acids on the stability of the proteins? figure 1. chemical structure of cysteine a the change has no effect on the stability of the protein because only one type of amino acid is involved. b the change leads to increased protein stability because of an increased number of s-s bonds in the tertiary structure of the proteins. c the change leads to decreased protein stability because of an increased number of s-s bonds in the tertiary structure of the proteins. d the change leads to increased protein stability only when the added cysteine amino acids are next to other cysteine amino acids in the primary structure.

Explanation:

To determine the effect of more cysteine on protein stability, we analyze each option:

• Option A: Incorrect. Cysteine affects stability via S - S bonds, so it does have an effect.
• Option B: Correct. Cysteine has an -SH group. More cysteine means more opportunities to form S - S bonds (disulfide bridges) in the protein's tertiary structure. These covalent bonds increase the protein's stability by holding the folded structure together more tightly.
• Option C: Incorrect. More S - S bonds (from more cysteine) should increase, not decrease, stability.
• Option D: Incorrect. The effect is on the tertiary structure (via S - S bonds), not just when cysteine is next to other cysteines in the primary structure.

Answer:

B. The change leads to increased protein stability because of an increased number of S - S bonds in the tertiary structure of the proteins.