Consider the observation that serine is the amino acid residue that can be replaced by another amino acid with the least effect on protein structure and function. Which of the following is the most reasonable rationalization of this observation?

a. Serine is the amino acid residue that can be replaced with the least effect on protein structure and function.

b. Replacement of tryptophan causes the greatest effect on protein structure and function.

c. Replacements such as Lys→ and Leu → usually have very little effect on protein structure and function.

The question has incorrect option, however the question can be answered by the general explanation. On the basis of the general explanation the answer is as follows:

Answer:

The correct answer is - Serine has a small side chain that can fit in any relatively polar environment.

Explanation:

Serine is an amino acid that have a small side chain in comparison of other amino acid and can be replaced by another amino acid with very least effect on the structure and function of a particular protein as they can fit in any relatively polar environment.

Serine have hydroxyl group in their side chain. It is polar amino acid that can easily establish itself in any polar condition and cause least changes in protein structure and function.

Thus, the correct answer is - Serine has a small side chain that can fit in any relatively polar environment.