Which of the following is not a non-essential amino acid?

Lysine is classified as an essential amino acid, which means that it cannot be synthesized by the body and must be obtained through diet. In contrast, alanine, glutamine, and serine are considered non-essential amino acids, which means the body can produce them even when they are not obtained directly from food sources.

Non-essential amino acids play crucial roles in various physiological functions, such as protein synthesis and metabolism. Understanding the distinction between essential and non-essential amino acids is critical for nutritional science and helps inform dietary choices and protein intake. Knowing which amino acids are essential can guide individuals, especially athletes or those with specific dietary restrictions, in meeting their nutritional needs effectively.