BI2BL5 Practical 1 Quiz 3

Peptides

1. The torsion angles which describe the protein backbone are:
a) Alpha, beta, gamma
b) Phi, psi, omega
c) Phi, psi, omega, chi

2. The phi angle is defined by the atoms
a) C-N-CA-C
b) CA-C-N-CA
c) N-CA-C-N

3. The psi angle is defined by the atoms
a) C-N-CA-C
b) CA-C-N-CA
c) N-CA-C-N

4. The omega angle is defined by the atoms
a) C-N-CA-C
b) CA-C-N-CA
c) N-CA-C-N

5. The peptide bond is:
a) A single bond
b) A double bond
c) A partial double bond

6. The nature of the peptide bond results from:
a) Delocalization of a lone pair of electrons on the carbonyl oxygen resulting in a partial positive charge on the oxygen and a partial negative charge on the backbone nitrogen
b) Delocalization of a lone pair of electrons on the backbone nitrogen resulting in a partial positive charge on the nitrogen and a partial negative charge on the carbonyl oxygen

7. The peptide bond is always:
a) Close to +/- 90 degrees
b) Close to 90 degrees
c) Close to 180 degrees
d) Close to 0 degrees
e) Freely rotatable
f) None of the above

8. Which direction corresponds to a positive torsion angle?
a) Moving the near atom anti-clockwise or the distant atom clockwise
b) Moving the near atom clockwise or the distant atom anti-clockwise

9. The peptide bond is often close to 0 degrees when the following amino acid is:
a) Glycine
b) Proline
c) Alanine
d) Tryptophan