**Core Concept**
Glutathione is a tripeptide antioxidant composed of three amino acids: cysteine, glutamate, and glycine. Its unique structure allows it to scavenge free radicals and detoxify harmful substances.

**Why the Correct Answer is Right**
The correct answer is glycine, which is essential for the formation of the disulfide bond between cysteine residues in glutathione. This disulfide bond is crucial for glutathione's antioxidant activity, enabling it to reduce oxidative stress and protect cells from damage. The presence of glycine also facilitates the recycling of glutathione, allowing it to maintain its antioxidant function.

**Why Each Wrong Option is Incorrect**
**Option A:** Glutamine is incorrect because, although it is a non-essential amino acid like glutamate, it is not a component of glutathione.
**Option B:** Histidine is incorrect because it is an essential amino acid with a different side chain and is not involved in the formation of glutathione.
**Option C:** Tyrosine is incorrect because it is an essential amino acid with a distinct side chain and is not a component of glutathione.

**Clinical Pearl / High-Yield Fact**
Glutathione plays a critical role in maintaining cellular redox balance and is often depleted in conditions like oxidative stress, trauma, and cancer. Its antioxidant function is essential for preventing cellular damage and promoting overall health.

**Correct Answer:** C. glycine.