Explain why the cartoon pictures of proteins often look like ribbons coiled and laying flat. Your description should include the shape of the NMA molecule's amide bond as well as the fact that all peptides that make up a protein are linked by amide bonds.

A peptide has the sequence: glu-trp-ser-gly-leu-lys-pro-gly What is the net charge of the molecule at pH 3,8,11 (only two side chain are ionizable).

Patients suffering from sickle cell anemia have a mutation in the gene that codes for one of the hemoglobin chains, in which a single glutamate is replaced by a valine. Propose an explanation for why this substitution has such a striking effect on protein structure and function with explanation.  Suggest two other amino acids that would be less likely to cause such serious impairment of hemoglobin function if each was substituted for glutamate. Briefly explain your answer.

It is often the case that a helices are positioned in a protein such that one side faces the interior of the protein and the other, the surface of the protein. These are said to be amphiphilic helices because they face different environments. Using a helical wheel projection (shown below), which of the peptide(s) below might form an amphiphilic helix? 8 15 1 12 4 11 16 18 9 7 14 13 10 17 O SLIKSVIEMVDEWFRTFL O FLIRVLRKVFRVLTRILS O RLFRSRVLKIAVIRFLLI