Acid-Base Properties of Amino Acids Practice Problems

Draw the prevalent form of asparagine present in a solution of pH 6.

Draw the predominant form of serine present in a solution of pH = 7.0. 

Draw the predominant form of serine present in a solution of pH = 12.0. 

Show the location and the type of charge on the tripeptide Gly-Ala-Ser at pH 6.0.

Show the location and the type of charge on the tripeptide Gly-Ala-Ser at pH 11.0.

Isoleucine has pK_a values of 2.36 and 9.68. Between what pH does isoleucine predominantly exist as a zwitterion?

Amino acid valine has pK_a values of 2.32 and 9.62. Determine the pH at which valine would exist in the following form.

Draw the predominant form of valine present in a solution with a pH of 6.

Draw the predominant forms of phenylalanine, tryptophan, and tyrosine present as a mixture at pH 7.

Draw the predominant form of threonine present in a solution with a pH of 12.

What is the predominant structure of tyrosine in solution at pH 4 ?

What are the predominant structures of valine, arginine, and glutamic acid in a solution with pH 3?

Asparagine and lysine both have nitrogen in their side chains, but the side chain of asparagine is non-basic, whereas the side chain of lysine is basic. Explain why the nitrogen in asparagine is more weakly basic than the nitrogen in lysine.

Neotame is a dipeptide ester used as an artificial sweetener. The full hydrolysis of neotame gives N-(3,3-dimethylbutyl)-aspartic acid, phenylalanine, and methanol. Treatment with carboxypeptidase enzyme shows no effect on neotame. Edman degradation of neotame gives phenylthiohydantoin derivative of N-(3,3-dimethylbutyl)-aspartic acid.
Suggest the structure for the neotame.

Provide all the possible protonation states of Lys arranged in increasing pH levels.

Draw a visual representation of Val, Glu, and Arg separated using electrophoresis at pH 6.