Question

Basic proteins consist of more basic amino acids and these amino acids exist as a cation at the physiological pH of 7.4.
Which among the following are basic amino acids?

• A. Lysine and Methionine
• B. Methionine and arginine
• C. Lysine and Valine
• D. Arginine and Lysine

Hint:

Basic amino acids = Lysine, Arginine, Histidine. Remember: “LAH” for quick recall.

Answer 1

The Correct Option is D

Concept:
Amino acids are classified based on the nature of their side chains (R-groups) into acidic, basic, and neutral amino acids. Basic amino acids have side chains that can accept protons and thus carry a positive charge (cation) at physiological pH (7.4).

Step 1: Identify basic amino acids. The common basic amino acids are:
• Lysine
• Arginine
• Histidine (weakly basic) These contain additional amino groups in their side chains, making them positively charged.

Step 2: Analyze the given options.
• (A) Lysine and Methionine → Methionine is neutral $\times$
• (B) Methionine and arginine → Methionine is neutral $\times$
• (C) Lysine and Valine → Valine is neutral $\times$
• (D) Arginine and Lysine → Both are basic amino acids \checkmark

Step 3: Conclusion. Thus, the basic amino acids are: \[ \text{Arginine and Lysine} \]