Amino Acids

Essential amino acids cannot be synthesized by the body and must be obtained from the diet.
- Lysine, Histidine, and Methionine are essential amino acids.
- Glutamine is a non-essential amino acid because the body can synthesize it. Thus, the correct answer is Glutamine.

1. Amino Acid I (Left Structure): The structure represents Leucine, which has a branched hydrocarbon side chain. Leucine is an essential amino acid, meaning it must be obtained from the diet.

2. Amino Acid II (Right Structure): The structure represents Serine, which contains a hydroxyl (-OH) group. Serine is a non-essential amino acid, meaning the body can synthesize it.

Thus, Amino Acid I (Leucine) is essential, and Amino Acid II (Serine) is non-essential, making option (3) the correct choice.