Which one of the following is a characteristic of the amino acid composition of a protein having an isoelectric pH (pI) of 4?
A) no neutral amino acids.
B) no basic amino acids.
C) no acidic amino acids.
D) more basic than acidic amino acids.
E) more acidic than basic amino acids.

Question

Quizplus · Accepted Answer

The isoelectric pH (pI) of a protein is the pH at which the net charge of the protein is zero. At this pH, the number of positive charges (from basic amino acids) is equal to the number of negative charges (from acidic amino acids). Therefore, a protein with a pI of 4 must have more acidic amino acids than basic amino acids. Furthermore, even though a protein with a pI of 4 could potentially have neutral amino acids, it is not a characteristic of the amino acid composition specifically related to its pI.

Which One of the Following Is a Characteristic of the Amino