biochemistry objective questions and answers

1. A weak acid can act as a buffer

a) at pH values = pK ± 0.1.
--> b) at pH values = pK ± 1.
c) at pH values = pK ± 2.
d) only at body temperatures.

2. Which of the following is considered to be a fibrous protein?

a) Hemoglobin
b) Immunoglobulin
--> c) Keratin
d) Myoglobin

3. Disulfide bonds most often stabilize the native structure of:

a) dimeric proteins.
--> b) extracellular proteins.
c) hydrophobic proteins.
d) intracellular proteins.

4. In sickle cell anemia, the basis of the malfunction of the hemoglobin molecule is:

a) faulty binding of the heme groups.
b) incorrect secondary structure.
c) reduced affinity for oxygen.
--> d) substitution of a single amino acid.

5. When BPG (2,3-Bisphosphoglycerate) binds to ______ site(s) on hemoglobin ________ its affinity for O2

a) four decreases.
b) four increases.
--> c) one decreases.
d) one increases.

6. The complementarity-determining regions (CDRs)

a) are found at the antigen-binding sites.
b) reside in the VL and VH regions of the IgG molecule.
c) reside in the CL and CH regions of the IgG molecule.
--> d) The first and second choices are both correct.

7. Antibodies of the IgG class

a) consist of four subunits.
b) are glycoproteins.
c) have inter- and intra-chain disulfide crosslinks.
--> d) All three choices are correct.

8. The RNA primers used to initiate replication in E. coli

a) are joined together by DNA ligase.
b) are removed by helicase + ATP.
--> c) are removed by Pol I "nick translation".
d) result in Okazaki fragments on the leading strand.

9. The two exonuclease activities of DNA polymerase I

a) are coupled during the formation of "gapped DNA".
b) degrade DNA in a 3' --> 5' direction.
c) degrade DNA in a 5' --> 3' direction.
--> d) occur at two different active sites.

10. On the ribosome, mRNA binds ____; the peptidyl transferase reaction occurs ____.

a) between the subunits; on the large subunit.
b) between the subunits; on the small subunit.
c) to the large subunit; on the small subunit.
--> d) to the small subunit; on the large subunit.

11. The pKa of an ionizable side chain, such as imidazole in histidine, can be determined with NMR because

a) protonated imidazole has twice the number of protons.
--> b) the chemical shift of His differs from that of His+.
c) the pKa is near neutrality.
d) unprotonated imidazole is invisible in the spectrum.

12. During the synthesis of a 100 residue protein, the number of GTP molecules used during initiation, elongation, and termination are, respectively:

a) 1, 100, 1.
--> b) 1, 198, 1.
c) 1, 200, 1.
d) 2, 198, 2.

13. Peripheral membrane proteins

a) are not accommodated by the fluid mosaic model.
b) are only of peripheral interest to membrane biologists.
--> c) can be dissociated from membranes relatively easily, e.g., high salt treatment.
d) can undergo transverse membrane motion, i.e. "flip-flop".

14. During glycolysis the following reaction requires NAD+:

a) Alcohol dehydrogenase
--> b) Glyceraldehyde-3-phosphate dehydrogenase
c) Lactate dehydrogenase
d) Pyruvate dehydrogenase
15. Since the energy released by all the reactions of glycolysis is 185 kJ/mol glucose, and ____ mol ATP is/are produced per mol glucose, the overall efficiency of glycolysis is about ____.

a) 1 16%
b) 1 33%
--> c) 2 33%
d) 2 50%

16. Glycogen digestion in the gut begins with a ________ reaction; intracellular glycogen breakdown begins with a ________ reaction.

a) hydrolysis; hydrolysis
--> b) hydrolysis; phosphorolysis
c) hydrolysis; phosphorylation
d) phosphorolysis; hydrolysis

17. The correct order, from fastest-acting to slowest, for the time scale of these regulatory mechanisms is:

--> a) Allosteric - covalent - genetic
b) Allosteric - genetic - covalent
c) Covalent - genetic - allosteric
d) Genetic - allosteric - covalent

18. Mitochondrial ATP synthesis requires

a) a [H+] gradient.
b) a membrane potential.
c) an intact inner mitochondrial membrane.
--> d) All three, a) - c).

19. Which of the following enzymes does not catalyze a physiologically irreversible step in glycolysis?

a) Hexokinase
b) Phosphofructokinase
--> c) Phosphoglycerate kinase
d) Pyruvate kinase

20. Following the addition of a mitochondrial respiratory inhibitor, components of the electron transport chain

a) all components will be oxidized.
b) downstream of the blockage will be reduced.
c) upstream of the blockage will be oxidized.
--> d) upstream of the blockage will be reduced.

21. For the following reaction:
[FAD] + 2 Cyt c (Fe2+) + 2H+ -> [FADH2] + 2 Cyt c (Fe3+)
the electron donor is _______; the reduced product is ________.

--> a) 2 Cyt c (Fe2+); [FADH2]
b) [FAD]; [FADH2]
c) 2 Cyt c (Fe2+); 2 Cyt c (Fe3+)
d) [FAD]; 2 Cyt c (Fe3+)

22. Acetyl groups (e.g. for lipid biosynthesis) are transported out of the mitochondria indirectly using

a) acetyl carnitine.
b) acetyl phosphate.
--> c) citrate.
d) malate.