Which of the following is not an essential amino add?
**Core Concept**
Essential amino acids are those that cannot be synthesized by the human body and must be obtained through the diet. They play a crucial role in various bodily functions, including protein synthesis, enzyme production, and hormone regulation.
**Why the Correct Answer is Right**
The human body cannot synthesize non-essential amino acids on its own, but it can produce essential amino acids through various metabolic pathways. Essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Non-essential amino acids, on the other hand, can be synthesized from other amino acids or intermediates in metabolic pathways.
**Why Each Wrong Option is Incorrect**
* **Option A:** Histidine is an essential amino acid as it cannot be synthesized by the human body.
* **Option B:** Lysine is an essential amino acid as it plays a critical role in various bodily functions, including protein synthesis and enzyme production.
* **Option C:** Glutamine is a non-essential amino acid as it can be synthesized from other amino acids, such as glutamate, through the action of the enzyme glutamine synthetase.
**Clinical Pearl / High-Yield Fact**
Non-essential amino acids can be converted into essential amino acids in some cases, but this process is not always efficient and may not meet the body's requirements. A diet rich in essential amino acids is essential for optimal protein synthesis and overall health.
**Correct Answer:** C. Glutamine.