When a Cysteine Residue in a Protein Is Replaced with Serine

question 135

Multiple Choice

When a cysteine residue in a protein is replaced with serine, the protein folds normally and exhibits 95 percent of its normal biological activity.However, when this same cysteine residue is replaced with glycine, the protein does not fold normally and exhibits only 35 percent of its normal biological activity.Which hypothesis is both reasonable and consistent with these observations?

• A) A hydrogen bond between the cysteine side chain and another residue in the interior of the protein helps stabilize the protein's tertiary structure.
• B) The cysteine side chain is exposed to the external environment, where it forms salt bridges with ions dissolved in the water surrounding the protein.
• C) The cysteine residue forms a disulfide bridge with another cysteine in the polypeptide chain to stabilize the protein's tertiary structure.
• D) A salt bridge between the cysteine side chain and an acidic residue in the interior of the protein helps stabilize the protein's tertiary structure.
• E) The cysteine side chain is located in a tight bend in the polypeptide chain, where only a small side chain can be accommodated.

---

Definitions:

Perversion

A deviation from what is considered normal or acceptable behavior, often with negative connotations relating to sexual behavior.

Hispanic

Relating to Spain or Spanish-speaking countries, especially those of Latin America. In the United States, often used to describe people of Spanish-speaking descent.

Native American

Indigenous peoples of the United States, including American Indians and Alaska Natives, with distinct cultural heritages, languages, and historical identities.

Class Shaming

The act of ridiculing or demeaning individuals based on their social class, often highlighting economic disparities and perpetuating stereotypes and discrimination.