3b) Both a-helical 2° structure and b-pleated sheet 2° structure result from the same type of interaction; briefly explain in your own words why you might observe an a-helix in one region of a protein and a b-pleated sheet in another region of the same protein.

Can the tertiary structure of a protein depend on the type of cell system used for synthesis? Explain.

Which of the following statements are False? (i)     Parallel b-sheets characteristically distribute hydrophobic side chains on both sides of the sheet, and antiparallel B-sheets are usually arranged with all their hydrophobic residues on one side of the sheet. (ii)   Planarity of the peptide bond means that no rotation occurs about the N-Ca bond while rotation is allowed about the C(O)-N and Ca-C(O) bonds. (iii) Silk fibers consist of fibroin proteins consisting of alternating A and G or S residues. (iv) If an aspartic acid residue were present in the interior of a globular protein, it would most likely be deprotonated and thus negatively charged.

Within a naturally-occurring polypeptide, under neutral pH conditions (pH = 7.0), which of the following amino acids always has a negatively charged carboxyl group? the first amino acid in the primary structure histidine lysine arginine the last amino acid in the primary structure