The electrophoresis of a mixture of histidine (His), aspartic acid (Asp) and phenylalanine (Phe) is carried out at a pH of 5.91. Match the amino acid to its predicted behaviour under electrophoresis at that pH.
1. This amino acid will bear no net charge at pH 5.91 and so will remain at the origin
2. This amino acid will carry a net negative charge at pH 5.91 and so will migrate towards the positive electrode
3. This amino acid will carry a net positive charge at pH 5.91 and so will migrate to the negative electrode
I need to match each amino acid to either 1, 2 or 3 but am not quite sure where to start on the question
I know that the pI (isoelectric points) for each amino acid are as follows:
His = pI 7.64
Asp = pI 2.98
Phe = pI 5.91
So I think that Phe will bear no net charge at 5.91 and will remain at the origin because it is at the pH where it is likely to be attracted to a positive or negative electrode equally. I am not sure what would happen with His and Asp though
I think that:
Phe = remain at origin (1)
Asp = migrate towards positive electrode (2)
His = migrate towards negative electrode (3)
Is this correct?
To determine the behavior of each amino acid under electrophoresis at pH 5.91, you need to consider the pKa values of the functional groups on the amino acid side chains and the pH of the environment.
1. Histidine (His):
Histidine has a pKa value of around 6.0 for its imidazole group. At pH 5.91, the imidazole group of histidine will be partially charged, with both positively and negatively charged forms present. The net charge would be close to zero, so histidine would bear no net charge at this pH and would remain at the origin (matching with #1).
2. Aspartic Acid (Asp):
Aspartic acid has a pKa value of around 3.9 for its carboxyl group and around 4.0 for its amino group. At pH 5.91, both groups would be negatively charged in their deprotonated forms. As a result, aspartic acid will carry a net negative charge and migrate towards the positive electrode (matching with #2).
3. Phenylalanine (Phe):
Phenylalanine does not have any acidic or basic functional groups that would contribute to its charge at pH 5.91. Therefore, it will not carry a net charge and will remain at the origin (matching with #1).
In summary, the matches are:
1. His - 1 (will remain at the origin)
2. Asp - 2 (will migrate towards the positive electrode)
3. Phe - 1 (will remain at the origin)