JEE Main · 2019 · Shift-ImediumBIO-120

The increasing order of pKa of following amino acids in aqueous solution is Gly, Asp, Lys, Arg

Biomolecules · Class 12 · JEE Main Previous Year Question

Question

The increasing order of pKa\text{pK}_a of following amino acids in aqueous solution is Gly, Asp, Lys, Arg

Options
  1. a

    Asp << Gly << Arg << Lys

  2. b

    Gly << Asp << Arg << Lys

  3. c

    Asp << Gly << Lys << Arg

  4. d

    Arg << Lys << Gly << Asp

Correct Answerc

Asp << Gly << Lys << Arg

Detailed Solution

Step 1: Classifying Residues — Amino acids are categorized by their nature: Acidic (Asp), Basic (Lys, Arg), and Neutral (Gly).

Step 2: Ranking Acidity/Basicity — The pKa\text{p}K_a values increase with basicity. Acidic Asp has the lowest value, neutral Gly is intermediate, and basic Lys and Arg have high values.

Step 3: Comparing Basics — Arginine is more basic than Lysine due to its guanidino group. Therefore, the order of increasing pKa\text{p}K_a is: Asp << Gly << Lys << Arg. Correct option is (c).

Key Point: The pIpI (isoelectric point) follows a similar trend based on these structural properties.

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