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INTRODUCTORY BIOCHEMISTRY
BIOL0280
Second Midterm Examination
April 2, 2015
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you with your exam after grading it. Please work independently. Read each question carefully
before answering. Unless otherwise indicated, there is only one correct answer for each
multiple-choice question. Points for each question are indicated within brackets []. There are
no calculators or other electronic devices needed or allowed on this exam. All hats
must be removed during the exam. Exams will be scanned electronically before being
returned.
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1. [4 points] Name the molecules shown in the figures.
___________________________
_______________________
2. [2 points] Which of the following is not true of the reaction catalyzed by the pyruvate
dehydrogenase complex?
A) Both NAD+ and a FAD act as electron carriers.
B) The reaction occurs in the mitochondrial matrix.
C) The substrate is held by the lipoyl-lysine “swinging arm.”
D) Biotin participates in the decarboxylation.
E) Two different cofactors containing —SH groups participate.
Circle the correct answer.
3. [4 points] In the citric acid cycle, we encountered a three-step mechanism to oxidize an
alkyl chain (shown in the figure). Name the four citric acid cycle intermediates (indicated with
letters next to the figure) that are involved in this mechanism.
_________________________________
A.
_________________________________
B.
_________________________________
C.
_________________________________
D.
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4. [2 points] The oxidative decarboxylation of α-ketoglutarate proceeds by means of multistep
reactions in which all but one of the following cofactors are required. Which one is not
required?
A) Coenzyme A
B) ATP
C) Lipoic acid
D) NAD+
E) Thiamine pyrophosphate
Circle the correct answer.
5. [2 points] Indicate whether the following statements are true or false by circling True or
False.
True / False
The citric acid cycle completely reduces the products of glycolysis to CO2
and generates oxidized cofactors as well as some ATP.
True / False
Anaplerotic reactions convert two-carbon molecules into four-carbon
molecules.
6. [3 points] List at least three factors that mitochondria and bacteria have in common.
7. [2 points] Which of the following statements about the chemiosmotic theory is false?
A) Electron transfer in mitochondria is accompanied by an asymmetric release of protons
on one side of the inner mitochondrial membrane.
B) Energy is conserved as a transmembrane pH gradient.
C) The membrane ATPase, which plays an important role in other hypotheses for energy
coupling, has no significant role in the chemiosmotic theory.
D) Oxidative phosphorylation cannot occur in membrane-free preparations.
E) The effect of uncoupling reagents is a consequence of their ability to carry protons
through membranes.
Circle the correct answer.
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8. [4 points] Indicate whether the following statements are true or false by circling True or
False.
True / False
The energy gained from NADPH re-oxidation is conserved in a proton
gradient.
True / False
Electrons that enter the electron transport chain from succinate
dehydrogenase bypass Complex I.
True / False
Cytochrome C is a small membrane anchored protein that transfers
electrons from Complex III to Complex IV.
True / False
The isolated F1 complex catalyzes ATP hydrolysis.
9. [2 points] Which of the following is not a feature of complex IV?
A)
B)
C)
D)
Cytochrome c is a one-electron donor.
Oxygen is a substrate.
Copper is an essential metal for the reaction.
For every electron passed to complex IV, two protons are consumed from the matrix (N)
side.
E) In order to generate two water molecules, complex IV must go through the catalytic
cycle two times.
Circle the correct answer.
10. [4 points] Glycolysis, the citric acid cycle, and oxidative phosphorylation are inhibited by
ATP. Briefly explain the purpose of this regulation by ATP.
11. [2 points] Rotation of the ______ subunit of ATP synthase causes conformational
changes in the catalytic sites that produce ATP.
A) α
B) β
C) δ
Circle the correct answer.
D) ε
E) γ
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12. [4 points] Explain in one or two sentences what accessory pigments are.
13. [2 points] Oxidative phosphorylation and photophosphorylation share all of the following
except:
A) chlorophyll.
B) involvement of cytochromes.
C) participation of quinones.
D) proton pumping across a membrane to create electrochemical potential.
E) use of iron-sulfur proteins.
Circle the correct answer.
14. [2 points] What is the soluble electron carrier in chloroplast photosystems, a molecule
analogous to cytochrome c in mitochondria?
A. Cytochrome c2
B. Cytochrome bc1
C. Plastocyanin
D. Rhodopsin
E. Ferredoxin
Circle the correct answer.
15. [3 points] Fill in the blanks in the following sentence describing the Calvin cycle:
For every 3 __________________ molecules fixed, 9 ATP and 6 _____________________
molecules are consumed and one molecule _______________________________________
is produced.
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16. [4 points] Briefly describe the strategy used by C4 plants to circumvent photorespiration.
17. [2 points] In humans, gluconeogenesis:
A) helps to reduce blood glucose after a carbohydrate-rich meal.
B) is activated by the hormone insulin
C) is essential in the conversion of fatty acids to glucose.
D) requires the enzyme hexokinase.
E) can result in the conversion of protein into blood glucose.
Circle the correct answer.
18. [4 points] Fill in the blanks in the following sentences:
The product of the enzyme PFK-2 is the molecule _______________________________.
The main storage polysaccharide in animal cells is ______________________________.
The enzyme that primes glycogen synthesis is called ____________________________.
Glycogen phosphorylase and glycogen synthase are ____________________________
regulated.
19. [2 points] The glycogen-branching enzyme catalyzes:
A) degradation of (α1 → 4) linkages in glycogen
B) formation of (α1 → 4) linkages in glycogen.
C) formation of (α1 → 6) linkages during glycogen synthesis.
D) glycogen degradation in tree branches.
E) removal of unneeded glucose residues at the ends of branches.
Circle the correct answer.
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20. [4 points] Briefly describe how fatty acids are transported from the cytosol into
mitochondria. Mention potential activation reactions and the import systems being used.
21. [2 points] Which compound is an intermediate of the β oxidation of fatty acids?
A) CH3—(CH2)20—CO—COOH
B) CH3—CH2—CO—CH2—CO—OPO32–
C) CH3—CH2—CO—CH2—OH
D) CH3—CH2—CO—CO—S—CoA
E) CH3—CO—CH2—CO—S—CoA
Circle the correct answer.
22. [2 points] The cofactor of propionyl-CoA carboxylase is
A) FAD
B) NADH
C) biotin
D) coenzyme B12
E) TPP
Circle the correct answer.
23. [3 points] Name the three molecules that function as ketone bodies in metabolism.
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24. [6 points] Fatty acid biosynthesis: In the space provided below, enter which molecule is
the carbon donor for synthesis, which enzyme synthesizes this carbon donor, which enzyme
then synthesizes fatty acids, what functions as the acyl carrier during synthesis, which cofactor
serves as the electron donor and which fatty acid is released from the synthesizing enzyme.
Carbon donor for fatty acid synthesis:
_________________________________
Synthesized by the enzyme:
_________________________________
Enzyme that synthesizes fatty acids:
_________________________________
Acyl carrier for synthesis:
_________________________________
Electron donor cofactor:
_________________________________
Fatty acid released:
_________________________________
25. [2 points] Name the molecule shown in the figure.
_________________________________
26. [2 points] Fill in the missing word(s).
Cholesterol-lowering drugs (statins) act as competitive inhibitors of the enzyme
___________________________________.
27. [2 points] Urea synthesis in mammals takes place primarily in tissues of the:
A) brain.
B) kidney.
C) liver.
D) skeletal muscle.
E) small intestine.
Circle the correct answer.
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28. [2 points] If a person's urine contains unusually high concentrations of urea, which one of
the following diets has he or she probably been eating recently?
A) High carbohydrate, very low protein
B) Very high carbohydrate, no protein, no fat
C) Very low carbohydrate, very high protein
D) Very, very high fat, high carbohydrate, no protein
E) Very high fat, very low protein
Circle the correct answer.
29. [4 points] Indicate whether the following statements are true or false by circling True or
False.
True / False
Aminotransferases have a thiamine pyrophosphate prosthetic group.
True / False
Major excretory forms of nitrogen are ammonia, urea, and uric acid.
True / False
In amino acid biosynthesis, glycine and proline are derived from 3phosphoglycerate.
True / False
Denitrifying bacteria reduce NO3- to N2.
30. [4 points] Briefly describe the bacterial process of nitrogen fixation.
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31. [3 points] List at least three factors affecting the activity of enzymes
32. [2 points] The molecule shown in the figure is
A. carnitine
B. ornithine
C. arginine
D. creatine
E. glyoxylate
Circle the correct answer.
33. [4 points] Indicate with a letter the cellular compartment where each of the following
metabolic pathways takes place (indicate with “C”ytosol, “M”atrix, “B”oth compartments):
_____ glycolysis
_____ β-oxidation
_____ fatty acid synthesis
_____ urea synthesis
34. [4 points] In the space provided, name the energy sources (molecules) for muscle
contraction during:
Light activity or rest
________________________________________________
Bursts of heavy activity
________________________________________________