Question

A mixture of glycine, alanine, aspartic acid, glutamic acid, leucine, lysine, histidine, asparagine, and phenylalanine are put into an electrophoresis apparatus, with the buffer pH=6.5. Sort each amino acid according to its charge in the buffer with a pH of 6.5.
a. Glycine
b. Alanine
c. Glutamic acid
d. Alanine aspartic acid
e. Leucine
f. Histidine asparagine
g. Phenylalanine
h. Lysine

Answer 1

Answer:

Positively charged:  Lysine, Histidine

Negatively charged:  Asparagine, Phenylalanine, Glutamatic acid, Alanine, Glycine, Leucine, Aspartic acid

Explanation:

The charge of an amino acid in solution is determined by its isoelectric point, pI, which is the characteristic pH in which the net electric charge of the amino acid is zero. In solutions of pH below the isoelectric point, the amino acid has a net positive charge whereas in solutions with pH above isoelectric point, the net charge on the amino acid is negative.

In a buffer solution of pH 6.5, the following charges are present in the amino acids given:

Positively charged:  Lysine (pI = 9.74), Histidine (pI = 7.59)

Negatively charged:  Asparagine (pI = 5.07), Phenylalanine (pI = 5.48), Glutamatic acid (pI = 3.22), Alanine (pI = 6.01), Glycine (pI = 5.97), Leucine (pI = 5.98), Aspartic acid (pI = 2.77)