Question

At physiological ph, the ionized state of the amino (nh2) group in the r group of lysine is:

Answer 1

At physiological pH, the ionized state of the amino group in the side chain of lysine is as an ammonium ion (−NH3+), due to the pKa of lysine being higher than the physiological pH.

Step-by-step explanation:

In the context of amino acid chemistry, lysine features an amino group in its side chain at physiological pH, typically around 7.4. Because amino groups in amino acid side chains tend to get protonated under these conditions, the ionized state of the amino group in lysine will be as an ammonium ion (−NH3+). The pKa of the side chain amino group of lysine is above physiological pH, falling between 9 to 11.

Therefore, at a pH of 7.4, it is expected to be protonated and carry a positive charge.This positive charge on lysine's side chain enhances its reactivity in biochemical processes, as it can participate in electrostatic interactions with negatively charged groups on other molecules. The protonation of lysine's amino group also plays a crucial role in the overall charge balance of proteins and peptides at physiological pH.

Answer 2

Physiological pH is between 7.37 and 7.43

Lysine is a basic amino acid, which means it has two NH2 groups and one COOH group.

Lysine pKas are: 2.16, 9.06 and 10.05

At low pH (lower than the first pKa, in this case: lower than 2.16) the three groups are protoned. As you increase pH, the first group to lose its proton is the acid group, then the alpha-amino group and then the R-amino group. You will have everything non protoned at a high pH (higher than the highest pKa, in this case: 10.05).

Physiological pH is higher than the lowest pKa and lower than the middle pKa, so it’s the second case: the acid is not protoned, the R-amino is protoned and the alpha amino is protoned.

Protoned aminos are cations: NH3+.