Question

Which of the following is a basic amino acid ?

• A. Serine
• B. Alanine
• C. Tyrosine
• D. Lysine

Answer 1

The Correct Option is D

To determine which amino acid is basic, we need to understand what makes an amino acid basic. Basic amino acids have a side chain (R-group) that can accept a proton (H⁺), making the overall molecule more positive. This characteristic is due to the presence of an amino group in their side chain, which is a common feature of basic amino acids.

1. Serine: Serine has a side chain with a hydroxyl group (-OH), which is neutral in its ionization properties. Thus, it is not a basic amino acid.
2. Alanine: Alanine has a side chain that is a simple methyl group (-CH₃), which is non-polar and neutral. Therefore, alanine is also not a basic amino acid.
3. Tyrosine: Tyrosine contains a phenol group in its side chain, which is a weak acid and not basic. Hence, tyrosine is not considered a basic amino acid.
4. Lysine: Lysine has a side chain that includes a primary amino group, which can accept a proton, making it basic. This additional amino group (NH₂) in the side chain gives lysine its basicity.

Therefore, the correct answer is Lysine, as it is the only amino acid listed with a side chain that acts as a base. Most often, basic amino acids like lysine are positively charged at physiological pH due to the protonation of the amino group.