Miscellanious

Question 1

Polypeptide Bond

(structure and 3 characteristics)

Answer 1

• amide linkage btwn a-carboxyl of one AA and a-amino of other
• 1. not broken by conditions that denature proteins, like heating or high conc of urea; prolonged exposure to strong acid or base at elevated temps is required to hydrolyze them nonenzymatically
• 2. has a partial double bond character (shorter than single bond, rigid and planar); prevents free rotation around bond btwn carbonyl C and N of peptide bond
• 3. Generally a trans bond bc of steric interference btwn R groups in cis

Question 2

Alpha Helix

Answer 2

• stabilized by extensive H bonding btwn peptide-bond carbonyl Os and amide Hs in polypeptide backbone
• extend up and are parallel to spiral from carbonyl O of one peptide bond to NH group of peptide linkage 4 residues ahead (n+4) - ensures sall but firs tand last peptide bond components are linked
• 3.6 AAs per turn; disrupted by proline (makes kink in chain), AAs with bulky side chain (Trp), or that branch at beta C (Val or Ile)

Question 3

Beta Sheets

Answer 3

• all peptide bond components involved in H bonding, but H bonds are perpendicular to polypeptide backbone
• surfaces of sheets are ‘pleated’, often visualized as large arrows
• unlike helix, composed of 2+ peptide chains (beta strands) or segments of polypeptide chains which are almost fully extended
• parallel or antiparallel; always have right-handed curl, or twist, in globular proteins