What is the net charge on the amino acid lysine at pH = 7.4 if pKa1 = 2.16, pKa2 = 9.06, and the pKa of the side chain = 10.54?A.+1B.+2C.0D.-1

To determine the net charge of an amino acid at a given pH, we need to consider the pKa values of its ionizable groups and compare them to the pH.

Lysine has three ionizable groups: the amino group (pKa1 = 2.16), the carboxyl group (pKa2 = 9.06), and the side chain (pKa = 10.54).

At pH 7.4:

1. The amino group (pKa1 = 2.16) will be protonated because the pH is above its pKa. This gives it a positive charge.

2. The carboxyl group (pKa2 = 9.06) will be deprotonated because the pH is below its pKa. This gives it a negative charge.

3. The side chain (pKa = 10.54) will be protonated because the pH is below its pKa. This gives it a positive charge.

So, the net charge of lysine at pH 7.4 is +1 - 1 + 1 = +1.

Therefore, the answer is A. +1.