91Ó°ÊÓ

Draw the structure of \((S)\) -proline.

Show the structures of the following amino acids in their zwitterionic forms: (a) Trp (b) Ile (c) Cys (d) His

Proline has \(\mathrm{p} K_{\mathrm{a} 1}=1.99\) and \(\mathrm{p} K_{\mathrm{a} 2}=10.60 .\) Use the HendersonHasselbalch equation to calculate the ratio of protonated and neutral forms at \(\mathrm{pH}=2.50\). Calculate the ratio of neutral and deprotonated forms at \(\mathrm{pH}=9.70\).

\- Using both three- and one-letter codes for amino acids, write the structures of all possible peptides containing the following amino acids: (a) Val, Ser, Leu (b) Ser, Leu \(_{2}\), Pro

Predict the product of the reaction of valine with the following reagents: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\), acid (b) Di-tert-butyl dicarbonate (c) \(\mathrm{KOH}, \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CH}_{3}\) COCl, pyridine; then \(\mathrm{H}_{2} \mathrm{O}\)

\- Show how you could use the acetamidomalonate method to prepare the following amino acids: (a) Leucine (b) Tryptophan

Write full structures for the following peptides: (a) C-H-E-M (b) E-A-S-Y (c) P-E-P-T-I-D-E

Show the steps involved in a synthesis of Phe-Ala-Val using the Merrifield procedure.

Draw the structure of the PTH derivative product you would obtain by Edman degradation of the following peptides: (a) \(\mathrm{I}\) -L-P-F (b) \(\mathrm{D}-\mathrm{T}-\mathrm{S}-\mathrm{G}-\mathrm{A}\)

The \(\alpha\) -helical parts of myoglobin and other proteins stop whenever a proline residue is encountered in the chain. Why do you think a proline is never present in a protein \(\alpha\) helix?