Question

Identify basic $\alpha$-amino acid from following.

• A. Alanine
• B. Lysine
• C. Asparagine
• D. Glycine

Hint:

The three common essential basic amino acids can be easily remembered using the mnemonic HAL: Histidine, Arginine, and Lysine!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the basic $\alpha$-amino acid among the given choices based on its structural side-chain properties.

Step 2: Key Formula or Approach:
Amino acids are classified as acidic, basic, or neutral depending on the relative number of amino groups ($\mathrm{-NH_2}$, basic) and carboxylic acid groups ($\mathrm{-COOH}$, acidic) present in their structure.

• Basic amino acids contain more amino groups than carboxylic groups in their structure (extra amino group in the side chain).

• Acidic amino acids contain an extra carboxyl group in their side chain.

• Neutral amino acids contain an equal number of amino and carboxyl groups.

Step 3: Detailed Explanation:
Let's classify each of the given options:

• Alanine: Contains one $\mathrm{-NH_2}$ and one $\mathrm{-COOH}$ group with a neutral methyl side chain ($\mathrm{-CH_3}$). (Neutral)

• Lysine: Contains an additional basic amino group in its side chain ($\mathrm{-(CH_2)_4NH_2}$), giving it two amino groups and one carboxyl group. (Basic)

• Asparagine: Contains an amide group ($\mathrm{-CONH_2}$) in its side chain, which is non-basic under physiological conditions. (Neutral)

• Glycine: The simplest amino acid with a hydrogen atom as its side chain. (Neutral)
Therefore, Lysine is the basic amino acid among the choices.

Step 4: Final Answer:
The basic $\alpha$-amino acid is Lysine, corresponding to option (B).