Question

BIOCHEMISTRY, PLEASE SHOW WORK THANK YOU: What is the net charge

of the following peptide at pH = 2? pH = 7? pH = 10? H3N-
SGRGKGAKLHR - COOH

Answer 1

The net charge of the peptide at pH 2 is positive, at pH 7 it is close to zero, and at pH 10 it is negative.

Step-by-step explanation:

The net charge of the peptide at different pH values can be determined by considering the ionization states of the amino acids in the peptide and their pKa values. At pH = 2, all the carboxylic acid groups (COOH) in the peptide will be protonated (pKa ~ 2) and have a positive charge. The amino groups (NH3+) of lysine (K) and arginine (R) will also be protonated and have a positive charge. Therefore, the net charge at pH = 2 will be positive.

At pH = 7, the carboxylic acid groups will be deprotonated and have a negative charge, while the amino groups will be protonated and have a positive charge. However, the net charge will be close to zero because the pKa values of the amino acids in the peptide are around 2 and 9, resulting in roughly equal amounts of protonated and deprotonated forms.

At pH = 10, the carboxylic acid groups will be deprotonated and have a negative charge, while the amino groups will also be deprotonated and neutral. Thus, the net charge will be negative.

Answer 2

The net charge of the peptide at different pH values depends on the ionization of its functional groups, glycine, and histidine. At pH 2, the peptide has a net positive charge. At pH 7 and 10, the peptide has a net negative charge.

Step-by-step explanation:

The net charge of a peptide at different pH values can be determined by considering the ionization of its functional groups. In this peptide, H3N-SGRGKGAKLHR-COOH, the amino acids glycine (Gly) and histidine (His) have ionizable groups. Glycine is neutral at all pH values, so it does not contribute to the net charge. Histidine has a pKa value of around 6, meaning that at pH values below 6, it will be mostly protonated, carrying a net positive charge. At pH values above 6, it will be mostly deprotonated, carrying a net negative charge.

1. At pH 2, the peptide will have a net positive charge because His will be mostly protonated.
2. At pH 7, the peptide will have a net negative charge because His will be mostly deprotonated.
3. At pH 10, the peptide will have a net negative charge because His will be mostly deprotonated.