Which of the following amino acids is classified as nonessential in humans?

• A. Threonine
• B. Alanine
• C. Leucine
• D. Lysine

Answer: (B)

Verified step by step guidance

1. Understand the classification of amino acids: Amino acids are categorized as essential or nonessential based on whether the human body can synthesize them. Essential amino acids must be obtained through the diet, while nonessential amino acids can be synthesized by the body.
2. Review the list of essential amino acids: Essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These cannot be synthesized by humans.
3. Identify nonessential amino acids: Nonessential amino acids include alanine, asparagine, aspartate, glutamate, glutamine, glycine, proline, serine, and tyrosine. These can be synthesized by the human body.
4. Compare the amino acids listed in the problem: Threonine, leucine, and lysine are essential amino acids, meaning they must be obtained through the diet. Alanine, on the other hand, is classified as nonessential because the human body can synthesize it.
5. Conclude that Alanine is the correct answer: Based on the classification, Alanine is the nonessential amino acid among the options provided.