Question

Aspartic acid is a polypeptide side chain found in proteins. The pKa of aspartic acid is 3.86. If this polypeptide were in an aqueous solution with a pH of 7, the side chain would have what charge? a) negative b) positive c) neutral d) there is no way to know

Answer 1

Answer: a) Negative

Explanation: According to the question: The pKa of aspartic acid is 3.86.

For acidic amino acids,

pH > pKa 

When side chains are negatively charged, amino acid will be acidic

pH < pKa 

That is, when side chains are uncharged, amino acid will be neutral

For aspartic acid, when this polypeptide were in an aqueous solution with a pH of 7

pH (7.0)  > pKa (3.86)

Therefore the chains are negatively charged