Question

At a pH above its pKa, the epsilon-amino group of lysine is ___.

a) Protonated
b) Deprotonated
c) Neutral
d) Positively charged

Answer 1

At a pH above its pKa, the epsilon-amino group of lysine is deprotonated, meaning the group has lost a proton and is neutral in charge.

Step-by-step explanation:

At a pH above its pKa, the epsilon-amino group of lysine is deprotonated. An amino acid like lysine, which contains a basic side chain, will have its epsilon-amino group in the form of -NH2 under physiological conditions (pH ~7.4). This group can accept protons and is considered basic, however, above the pKa of the epsilon-amino group, the group is more likely to be in the -NH2 form rather than its protonated -NH3+ form, thus it is generally deprotonated and has a neutral charge at a higher pH.