What maintains the secondary structure of protein: A) peptide bond. B) Hydrogen bonds between the amino group of one peptide bond and the carboxyl group of another peptide bond. C) Hydrogen bonds between the R group of one amino acid and the carboxyl group og another peptide bond. D) disulfide bonds. E) Hydrophobic interactions.

Peptide bonds cannot rotate. This is because: a) the amino acid side chains are too bulky to allow this. B) Internal hydrogen bonding hinders rotation.   C) interaction with water molecules hinders rotation  D) the peptide bond has considerable double bond character Polypeptide chains prefer the trans conformation. This is because: a) This distances hydrophilic groups from hydrophobic groups b) this minimizes crowding of side chains   c) This brings hydrophilic groups in contact with water molecules   d)  This allows proteins to fold more easily Ramachandran plots indicate that protein conformation is largely a function of: a) hydrophobicity b)  number of amino acids   c) torsion angles    d)  arrangement of prosthetic groups

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.

3. Which best describes the contribution of tertiary (3’) structure of to the native conformation of polypeptides and proteins: a) Structure that results from intrachain interactions of amino acid side chains b) Structure that results from interchain interactions of amino acid side chains c) Structure that results from base pairing d) Structure that results from the linear sequence of amino acids from beginning to end of molecule