Question

Which of the following is NOT a basic amino acid?

• A. Proline
• B. Lysine
• C. Arginine
• D. Histidine

Hint:

Basic amino acids have side chains that are positively charged at physiological pH. Look for amino or guanidino groups in the side chain.

Answer 1

The Correct Option is A

Concept:
Basic amino acids are those amino acids whose side chains can accept a proton and become positively charged. Common basic amino acids are:

• Lysine
• Arginine
• Histidine

These contain extra nitrogen-containing basic groups in their side chains.
Step 1: Check Proline
Proline has a cyclic secondary amino structure. Its side chain is nonpolar and does not contain an extra basic group. \[ \Rightarrow \text{Not a basic amino acid} \]
Step 2: Check Lysine
Lysine contains an extra terminal amino group: \[ -(CH_2)_4NH_2 \] This group can accept proton. \[ \Rightarrow \text{Basic amino acid} \]
Step 3: Check Arginine
Arginine contains guanidino group. This group is strongly basic. \[ \Rightarrow \text{Basic amino acid} \]
Step 4: Check Histidine
Histidine contains imidazole ring. It shows weak basic nature. \[ \Rightarrow \text{Basic amino acid} \]
Step 5: Final Answer
The amino acid which is not basic is: \[ \boxed{\text{Proline \] Quick Tip:
Remember basic amino acids as: \[ \text{Lysine, Arginine, Histidine} \] All others among common options are usually neutral or acidic.