**Core Concept:** Sulphur-containing amino acids are essential building blocks of proteins and are essential for various biological functions in the body. There are two types of sulphur-containing amino acids: cysteine and methionine. These amino acids are part of the R-group of proteins and play a crucial role in protein synthesis, antioxidant defense, and detoxification.

**Why the Correct Answer is Right:**

Sulphur-containing amino acids are essential for protein synthesis and maintaining the structure and function of proteins. Among the given options, cysteine and methionine are the correct answers as they are the two types of sulphur-containing amino acids. Cysteine is involved in the formation of disulfide bonds, which are crucial for protein structure and function. Methionine is involved in the synthesis of creatine, an important energy-storing compound in the body. Both amino acids are involved in antioxidant defense, immune function, and detoxification processes.

**Why Each Wrong Option is Incorrect:**

Option A (tryptophan) and option B (tyrosine) are not sulphur-containing amino acids. Tryptophan is an essential amino acid involved in serotonin and melatonin synthesis, but it does not contain sulphur. Tyrosine is essential for the synthesis of catecholamines (epinephrine, norepinephrine, and dopamine) and melanin production, but it does not contain sulphur.

Option C (histidine) is another essential amino acid involved in protein synthesis and immune function. However, unlike cysteine and methionine, histidine does not contain sulphur.

**Clinical Pearl:**

Understanding the unique roles of essential amino acids, such as cysteine, methionine, and the other amino acids mentioned above, is crucial for appreciating their physiological significance in protein synthesis and maintaining cellular health. Adequate intake of these amino acids is essential for optimal protein synthesis and ensuring the body's antioxidant defense, detoxification, and immune function.

**Correct Answer:**

The correct answer is **C. histidine**. Histidine is an essential amino acid that plays a crucial role in protein synthesis and immune function. However, it does not contain sulphur, making it different from cysteine and methionine.