Question

In the protonated form of lysine, the positive charge is localized on one nitrogen atom. In the protonated form of arginine, the charge is delocalized on 3 nitrogen atoms. Why does this explain why the side chain of arginine has higher pKa than the side chain of lysine?

Answer 1

`pK_a` of arginine is higher than that of lysine.

Step-by-step explanation:

1. According to the Bronsted-Lowry acid-base theory, a stronger base will have a weak conjugate acid.

The positive charge is more stable on
`sp^3` hybrid atom as compared to
`sp^2` hybrid atom.

Therefore, arginine is more basic as compared to lysine.

2. Moreover, 3 nitrogen atoms are present in arginine that has the capability to accept acidic protons as compared to the one nitrogen that is present in lysine.

Higher the
`pK_a`, higher will be the basicity.

Therefore,
`pK_a` of arginine is higher than that of lysine.