3.11) Draw the structural formula for the predominant form of Asp-Gly-Lys-Ala at physiological pH. Lone pairs are optional. :0: HH I. I || H-N-C-C-0: H CH₂2 -Ö: :0: naportin noid H H :0: I. I || H-N-C- с I H H ekaina :0: H H I 1 || H-N-C-C-0: H CH, CH₂ ϲ CH₂ T CH₂ H-N-H H kaino :0: HH 1. III H-N-C-C-0: I H CH₁ ploning HINT: Peptides are often identified by listing its amino acid residues' three-letter abbreviations in order from N-terminus to C-terminus. To begin, draw the four amino acids side-by-side (as shown on the right) and then connect them in the same manner that was used for the dipeptide in problem 13.7

The carbon-nitrogen peptide bond is rigid, but rotation can take place about the N-C, and the Co-C bonds in a protein (Co is the a carbon atom). These bond angles define the conformation of the peptide chain. Consider the Ramachandran plot to answer both questions. Which observation most likely describes part of an observed a helix? = −60°; y = −47°; many Ala residues -59°; y = +150°; many Ser residues -57°; y = -47°; many Pro residues -140°; y = +130°; many Val residues +60°; y = +40°; many Gly residues Φ $ = Φ $ = = = (degrees) 180 120 60 O -60 -120 -180 -180 0 (degrees) 180

Why is peptide synthesis carried out from C terminus to N terminus using dicyclohexylcarbodiimide (DCC)? Can you illustrate the explanation with a mechanism/drawing?

Report the isoelectric point of the peptide, Gly-Asp-Lys-Ile?

Draw the full structure of the following tetrapeptide. Label the N-terminal and C-terminal residues.   Phe-Cys-Ser-Ile

Draw resonance structures for a peptide bond between Tyr and Pro.

Draw the Fischer projections representing the L forms of the following amino acids at pH lower than their isoelectric point. a) valine b) threonine

Identify the terminal amino group of this dipeptide of arginine and aspartic acid. Click on the N-terminus. HN: HN Targets placed: 0/1 You can place up to 1 targets NH₂ HO O - NH NH, -OH Undo Delete selected Remove All

6. Draw any cyclic peptide that you choose. Is there any way to tell where the N-terminal and C- terminal are?

How to show the cyclization of frontalin