Chapter 4: Amino Acids

Draw the structure of Lys and Ala linked by an Isopeptide bond.

Lanthionine is a nonstandard amino acid consisting of two alanine residues linked via their β carbon atoms by a thioether (—S—) linkage. Draw the structure of lanthionine.

Draw the dipeptide Asp-His at pH 7.0

Explain why all the amino acids except for glycine are chiral.

Calculate the number of possible pentapeptides that contain one residue each of$\mathbf{\text{Ala, Gly, His, Lys,}}$ and $\mathbf{\text{Val}}$.

In some proteins, the side chain of serine appears to undergo ionization. Explain why ionization would be facilitated by the presence of an aspartate residue nearby.

Determine the net charge of the predominant form of Asp at (a)pH 1.0, (b) pH 3.0, (c)pH 6.0, and (d) pH 11.0.