Bio 2020 midterm

Topics: Protein, Amino acid, Protein structure Pages: 10 (1853 words) Published: September 20, 2014
SC/BIOL 2020.03
Biochemistry
Midterm #1

Name:

Student ID:
Feb 7th, 2013
Time: 1 hr and 15 min
This test has multiple choice: 24 Marks.
Fill in the blanks: 10 Marks
Peptide structure: 6 Marks
There are a total of 10 pages of this exam.
You are allowed to use a non-programmable
calculator.
For multiple choice: Choose the BEST answer and
indicate your choice on the scantron. Please use a
pencil.
1

1. Which of the following weak interactions is NOT due to differences in electrical charge distribution?
a)
b)
c)
d)
e)

hydrophobic interactions.
hydrogen bonds.
dipole-diople interactions.
ionic interactions.
London dispersion forces.

2. Which of the following amino acids could form a hydrogen-bonding interaction between their R groups?
a) Glutamine and Alanine
b) Glutamine and Valine
c) Glutamine and Phenylalanine
d) Glutamine and Isoleucine
e) Glutamine and Tryptophan
3. There are several amino acid side chains that are always charged at physiological pH. These are:
a)
b)
c)
d)

Gln, Asn, Lys, and Arg.
Glu, Asp, Lys, and Arg.
Lys, His, and Arg.
Glu, Asp, Lys, Arg, and His.

4. After synthesis, a globular protein spontaneously folds because: a) water interacts with polar residues on the protein surface. b) nonpolar residues coalesce through the hydrophobic effect. c) disulphide bridges form.

d) thermal energy randomly achieves the most stable conformation. e) polar residues form hydrogen bonds within the protein.
5. If an aqueous solution has a hydrogen ion concentration of 10 -5 M what is the concentration of the hydroxyl ion?
a) 10-5 M
b) 10-7 M
c) 10-9 M
d) 10-11 M

2

e) 10-13 M

6. An acid, HA, has a concentration of 0.075 M and its conjugate base, A- ,has a concentration of 0.025M at pH 6. What is the pKa of HA?
a)
b)
c)
d)
e)

5.52
6.48
6.00
7.60
8.13

7. A BIO 2020 student does a Western blot, shown below. Unfortunately the Western blot reveals 5 different bands, due to the poor specificity of the antibody. Which band is most likely the right one given the protein of interest is 200 amino acids in length? A molecular weight ladder is given to the left. 72

55
kD
kD
43
kD
34
kD
26
kD

A
B
C
D

17
kD

E

8. An alpha helix is a secondary structure that is characterized by: a) Every C=O in the polypeptide backbone has a hydrogen bond to an N-H group 4 residues along the helix.
b) The C=O in the polypeptide backbone hydrogen bonds with N-H groups in an adjacent helix backbone.
c) Proline is modified to hydroxyl-proline which allows hydrogen bonding within the helix.
d) Mostly random coil regions, characterized by proline residues. e) Hydrogen bonding of R-groups on the outside of the helix with water. 9. The initial O2 molecule to bind to the hemoglobin protein results in:

3

a)
b)
c)
d)
e)

the dissociation of other O2 molecules that were previously bound. a decrease in hemoglobin's affinity to bind a second O 2.
dissociation of the hemoglobin subunits.
the diffusion of oxygen into muscle tissue.
an increased affinity for O2 in the remaining subunits.

10. Noncovalent forces that stabilize protein structure include all of the following except ?
a)
b)
c)
d)
e)

the hydrophobic effect
salt bridges
electrostatic interactions with metal ions
hydrogen bonding
disulfide bridges

11. If Histidine 143 in hemoglobin was mutated, so that 2,3Bisphophateglycerate was no longer able to bind, what would be the effect? a) Heme would no longer be able respond to oxygen binding, and therefore allosteric regulation of hemoglobin would be lost.

b) This would lead to hemoglobin aggregation and thus sickle cell anaemia. c) Hemoglobin would have a higher affinity for oxygen, favouring the R state. d) Hemoglobin would have a lower affinity for oxygen, favouring the T state. e) Carbon dioxide would no longer have an effect on hemoglobin, favouring R-state.

12. Where do anti-parallel β sheets fall on the
Ramachandran...
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