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INTRODUCTORY BIOCHEMISTRY
BIOL0280
Second Midterm Examination
April 5, 2012
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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
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1. [4 points] Match each enzyme or protein to one or more of the cofactors listed.
Aconitase ____D______
A. Thiamine pyrophosphate
B. Lipoic acid
Pyruvate carboxylase ____C______
C. Biotin
D. Iron-sulfur cluster
Pyruvate dehydrogenase ____A,B,E,F______
E. Coenzyme A
F. FAD
α-Ketoglutarate dehydrogenase ____A,B,E,F______
2. [2 points] What is the name of the
molecule shown to the right?
__citrate____
3. [2 points] Indicate with asterisks (*)
which carbon atom(s) of this molecule
would be derived from oxaloacetic acid
in a single turn of the citric acid cycle.
COOH
|
CH2
|
HO-C*-C*OOH
|
H-C*-H
|
C*OOH
4. [2 points] In mammals, each of the following occurs during the citric acid cycle except:
A) formation of α-ketoglutarate.
B) generation of NADH and FADH2.
C) condensation of acetylCoA and oxaloacetate to form citrate
D) net synthesis of oxaloacetate from acetyl-CoA.
E) oxidation of acetyl-CoA.
Circle the correct answer
5. [2 points] Conversion of 1 mol of acetyl-CoA to 2 mol of CO2 and CoA via the citric acid cycle
results in the net production of:
A) 1 mol of citrate.
B) 1 mol of FADH2.
C) 1 mol of NADH.
D) 1 mol of oxaloacetate.
E) 7 mol of ATP.
Circle the correct answer
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6. [2 points] Name an enzyme that catalyzes an anaplerotic reaction, and name its cofactor.
Enzyme: Pyr carboxylase, PEP carboxykinase, PEP carboxylase, or malic enzyme
Cofactor: biotin_____
7. [2 points] A water-soluble component of the electron transport chain that can diffuse freely in the
intermembrane space and can carry electrons is ______________.
A) ubiquinone
B) 2,3-BPG
C) cytochrome c
D) cytochrome oxidase
E) heme
Circle the correct answer
8. [2 points] Which of the following statements about the chemiosmotic theory is correct?
A) Electron transfer in mitochondria is accompanied by an asymmetric release of protons on
one side of the inner mitochondrial membrane.
B) It predicts that oxidative phosphorylation can occur even in the absence of an intact inner
mitochondrial membrance.
C) The effect of uncoupling reagents is a consequence of their ability to carry electrons through
membranes.
D) The membrane ATP synthase has no significant role in the chemiosmotic theory.
E) All of the above are correct.
Circle the correct answer
9. [2 points] In the reoxidation of QH2 by purified ubiquinone-cytochrome c reductase (Complex III)
from heart muscle, the overall stoichiometry of the reaction requires 2 mol of cytochrome c per mole
of QH2 because:
A) cytochrome c is a one-electron acceptor, whereas QH2 is a two-electron donor.
B) cytochrome c is a two-electron acceptor, whereas QH2 is a one-electron donor.
C) cytochrome c is water soluble and operates between the inner and outer mitochondrial
membranes
D) heart muscle has a high rate of oxidative metabolism, and therefore requires twice as much
cytochrome c as QH2 for electron transfer to proceed normally.
E) two molecules of cytochrome c must first combine physically before they are catalytically active.
Circle the correct answer
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10. [5 points] In the mitochondrial electron transport chain, which (one or more) of the macromolecular
complexes (I, II, III, IV):
Move(s) H+ into intermembrane space? _____I,III,IV_________
Contain(s) essential copper ions? ____IV______
Contain(s) a bound FAD cofactor? ___II_______
Interact(s) with cytochrome c? ___III, IV_______
Interact(s) with ubiquinone? __I,II,III________
You must indicate all correct answers to receive credit.
11. [1 point] How many catalytic adenylate-binding sites does ATP synthase contain? __3____
12. [1 point] Indicate whether the following statement is true or false by circling T or F.
T / F
ATP synthase binds ADP with higher affinity than ATP.
13. [1 point] Name the shuttle system that transfers cytosolic NADH redox equivalents to the
mitochondrial matrix for re-oxidation:
_____Malate-Aspartate Shuttle_______________
14. [6 points] For each of the six processes or components listed below, indicate whether it is
associated with Photosystem I, Photosystem II, or both Photosystems in plants by circling the correct
answer.
Pheophytin I / II / Both
Ferredoxin
I / II / Both
Oxygen-evolving complex
I / II / Both
Cyclic photophosphorylation
I / II / Both
Noncyclic photophosphorylation
I / II / Both
Plastoquinone
I / II / Both
Circle the correct answer for each.
15. [2 points] Photosynthetic phosphorylation and oxidative phosphorylation appear to be generally
similar processes, both consisting of ATP synthesis coupled to the transfer of electrons along an
electron carrier chain. Which of the following is not true of both processes?
A) Both contain cytochromes and flavins in their electron carrier chains.
B) Both processes are associated with membranous elements of the cell.
C) Both use oxygen as a terminal electron acceptor.
D) Each represents the major route of ATP synthesis in those cells in which it is found.
Circle the correct answer
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16. [2 points] What is the name of the compound pictured at the right?
____ribulose 1,5 bisphosphate______________
*----->
17. [2 points] Indicate with (an) asterisk(s) (*) which carbon atom(s) of this
compound react(s) with CO2 in the CO2-fixation step of the Calvin cycle.
18. [2 points] Identify an alternative molecule that this compound reacts with.
___O2___
19. [2 points] Which one of the following statements about gluconeogenesis is false?
A) For starting materials, it can use carbon skeletons derived from certain amino acids.
B) It consists entirely of the reactions of glycolysis, operating in the reverse direction.
C) It employs the enzyme glucose 6-phosphatase.
D) It is one of the ways that mammals maintain normal blood glucose levels between meals.
E) It requires metabolic energy (ATP or GTP).
Circle the correct answer
20. [2 points] All of the following enzymes involved in the flow of carbon from glucose to lactate
(glycolysis) are also involved in the reversal of this flow (gluconeogenesis) except:
A) phosphoglycerate mutase.
B) aldolase.
C) enolase.
D) phosphofructokinase-1.
E) phosphohexose isomerase.
Circle the correct answer
21. [2 points] The molecule above is a(n)
A) substrate for gluconeogenesis
B) product of gluconeogenesis
C) competitive inhibitor of key enzymes in glycolysis and gluconeogenesis
D) allosteric regulator of key enzymes in glycolysis and gluconeogenesis
Circle the correct answer
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22. [2 points] Which of the following substrates cannot contribute to net gluconeogenesis in
mammalian liver?
A) alanine
B) glutamate
C) palmitate
D) pyruvate
Circle the correct answer
23. [5 points] In the spaces below, write the correct terms missing in the
figure to the right.
A) ___β oxidation_______________________
B) ___acetyl-CoA_______________________
C) ___citric acid cycle____________________
D) ___NADH/FADH2____________________
E) ___Respiratory(electron-transport) chain___
24. [2 points] Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires:
A) ATP, carnitine, and coenzyme A.
B) ATP, carnitine, and pyruvate dehydrogenase.
C) ATP, coenzyme A, and hexokinase.
D) ATP, coenzyme A, and pyruvate dehydrogenase.
E) carnitine, coenzyme A, and hexokinase.
Circle the correct answer
25. [3 points] Briefly describe the function of glycogenin in glycogen synthesis
Ans. Glycogenin is required to initiate the formation of a new glycogen molecule. It catalyzes the
formation of an eight-residue polyglucose primer that serves as a substrate for glycogen synthase.
Glycogenin remains covalently bound to the glycogen molecule.
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26. [2 points] Which of the following statements apply (applies) to the β oxidation of fatty acids?
1. The process takes place in the cytosol of mammalian cells.
2. Carbon atoms are removed from the acyl chain one at a time.
3. Before oxidation, fatty acids must be converted to their CoA derivatives.
+
4. NADP is the electron acceptor.
5. The products of β oxidation can directly enter the citric acid cycle for further oxidation.
A) 1 and 3 only
B) 1, 2, and 3
C) 1, 2, and 5
D) 3 and 5 only
E) 4 only
Circle the correct answer
27. [6 points] The synthesis of fatty acids and their breakdown by β-oxidation occur by separate
pathways. Compare the two paths by filling in the table below.
Synthesis
b oxidation
——————————————————
Electron carrier coenzyme(s) ____NADPH________________NAD+_______
Basic units added or removed ___malonyl-_______________acetyl-_________
Cellular location of process
___cytosol___________mitochondrial matrix___
28. [2 points] Which of the following is not an intermediate in the synthesis of lanosterol from acetylCoA?
A) Isopentenyl pyrophosphate
B) Malonyl-CoA
C) Mevalonate
D) Squalene
Ε) β-Hydroxy-β-methylglutaryl-CoA (HMG-CoA)
Circle the correct answer
29. [2 points] Palmitoyl-CoA is a direct precursor of:
A) cholesterol.
B) malonyl-CoA.
C) mevalonate
D) sphingosine.
E) squalene.
Circle the correct answer
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30. [2 points] In amino acid catabolism, the first reaction for most amino acids is a(n):
A) decarboxylation requiring thiamine pyrophosphate (TPP).
B) hydroxylation requiring NADPH and O2.
C) oxidative deamination requiring NAD+.
D) reduction requiring pyridoxal phosphate (PLP).
E) transamination requiring pyridoxal phosphate (PLP).
Circle the correct answer
31. [2 points] Which substance is not involved in the production of urea from NH4+ via the urea cycle?
A) Aspartate
B) ATP
C) Carbamoyl phosphate
D) Malate
E) Ornithine
Circle the correct answer
32. [2 points] The ___aspartate____________ - _____argininosuccinate_______________________
shunt links the urea cycle with the citric acid cycle.
33. [3 points] Degradation of amino acids yields compounds that are common intermediates in the
major metabolic pathways. Explain the distinction between glucogenic and ketogenic amino acids in
terms of their metabolic fates.
Ans: The glucogenic amino acids are those that are catabolized to intermediates that can serve
as substrates for gluconeogenesis(1.5 pts): pyruvate and any of the four- or five-carbon
intermediates of the citric acid cycle. Ketogenic amino acids are catabolized to yield acetylCoA or acetoacetyl-CoA, the precursors for ketone body formation. (1.5 pts)
34. [3 points] Why does a mammal go to all of the trouble of making urea from ammonia rather than
simply excreting ammonia as many fish do?
Ans: When fish release ammonia into the surrounding medium, it is diluted enormously to
nontoxic levels. The ammonia produced by amino acid catabolism in mammals cannot be
sufficiently diluted in the tissues and the blood to avoid accumulating at toxic levels. Urea is
much less toxic than ammonia.
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35. [2 points] Which of the following statements about the fixation of atmospheric nitrogen (N2) into
NH3 by living cells is false?
A) It involves the transfer of 8 electrons per mol of N2.
B) It occurs in certain microorganisms, but not in humans.
C) It requires a source of electrons, normally ferredoxin.
D) It requires one ATP per mol of N2 fixed.
E) It requires two key protein components
Circle the correct answer
36. [2 points] The relative concentrations of ATP and ADP control the cellular rates of:
A) glycolysis.
B) oxidative phosphorylation.
C) pyruvate oxidation.
D) the citric acid cycle.
E) all of the above.
Circle the correct answer
37. [2 points] Which one of the following statements is true?
A) The brain prefers glucose as an energy source, but can use ketone bodies.
B) Muscle cannot use fatty acids as an energy source.
C) The brain exports ketone bodies as fuels for other tissues.
D) Fatty acids cannot be used as an energy source in humans because humans lack the enzymes of
the glyoxylate cycle.
E) Heart muscle stores fuel as glycogen.
Circle the correct answer
38. [3 points] Describe three possible fates for glucose 6-phosphate in the liver.
Ans: Possible answers include: (1) conversion to liver glycogen; (2) dephosphorylation and
release of glucose into bloodstream; (3) oxidation via the pentose phosphate pathway; (4)
oxidation via glycolysis and the citric acid cycle; (5) oxidation to acetyl-CoA, which then serves
as precursor for synthesis of triacylglycerols, phospholipids, and cholesterol.
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39. [2 points] When blood glucose is abnormally low, the pancreas releases:
A) epinephrine.
B) glucagon.
C) glucose.
D) insulin.
E) trypsin.
Circle the correct answer
40. [2 points] Which of the following is not involved in signal transduction by the β-adrenergic receptor
pathway?
A) ATP
B) Cyclic AMP
C) Cyclic GMP
D) GTP
E) All of the above are involved.
Circle the correct answer
41. [3 points] The insulin signaling pathway regulates the activity of glycogen synthase through GSK3
and PKB. Briefly explain how this regulation works. Your answer should include for all three
enzymes whether phosphorylation activates or inactivates the enzyme and how they interact with
each other.
Insulin pathway phosphorylates and activates PKB kinase which phosphorylates and inactivates
GSK3. Active GSK3 phosphorylates and inactivates glycogen synthase. Active glycogen synthase
produces glycogen. So when insulin is present, glycogen synthase is active.