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

1. Asp < Gly < Lys < Arg
2. Arg < Lys < Gly < Asp
3. Gly < Asp < Arg < Lys
4. Asp < Gly < Arg < Lys

Correct answer: Asp < Gly < Lys < Arg

Solution

The pKa values of amino acids reflect their side chain acidity; as the side chain becomes more acidic, the pKa decreases. Aspartic acid has the lowest pKa due to its carboxyl side chain, followed by glycine, lysine, and arginine, which have progressively higher pKa values due to their basic side chains.

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