Side chain of which amino acid contains sulfhydryl group –
**Core Concept**
The question is testing the knowledge of amino acid structure, specifically the side chains of various amino acids. Amino acids are the building blocks of proteins, and their side chains determine their properties and functions. The **sulfhydryl group** is a functional group that contains a sulfur atom bonded to a hydrogen atom.
**Why the Correct Answer is Right**
The correct answer is Cysteine, as its side chain contains a **sulfhydryl group** (-SH). This group is responsible for the unique properties of cysteine, including its ability to form disulfide bonds with other cysteine molecules. Cysteine plays a crucial role in the structure and function of many proteins, including enzymes, hormones, and transport proteins.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the side chain of this amino acid does not contain a sulfhydryl group.
**Option B:** Similarly, this option is incorrect as it lacks a sulfhydryl group in its side chain.
**Option D:** This option is also incorrect because its side chain does not contain a sulfhydryl group.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that cysteine is the only amino acid that contains a **sulfhydryl group**, which makes it unique in terms of its chemical properties and biological functions. This knowledge is crucial in understanding various biochemical processes, including protein synthesis and modification.
**Correct Answer:** C. Cysteine.