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FINAL EXAM OF CHE302: BIOCHEMISTRY
Date: December 30, 2015
Max: 50 Marks
Duration: 2 hours
Instructions
You have 100 minutes for this exam.
Exams written in pencil or erasable ink will not be re-graded under any circumstances.
Explanations should be concise and clear.
You do not need a calculator for this exam, and no other study aids or materials are permitted.
Generous partial credit will be given, i.e., if you don’t know, guess.
Honor Pledge: At the end of the exam time, please write out the following sentence and sign it:
“I pledge on my honor that I have not given or received any unauthorized assistance on this
examination.”
Questions
1. Compare and contrast fatty acid oxidation and synthesis with respect to: /6 marks
(a) site of the process.
(b) acyl carrier.
(c) reductants and oxidants.
(d) stereochemistry of the intemediates.
(e) direction of synthesis or degradation.
(f) organization of the enzyme system.
2. What is the role of decarboxylation in fatty acid synthesis? Name another key reaction in a
metabolic pathway that employs this mechanistic motif. /2 marks
3. Peroxisomes have an alternative pathway for oxidizing polyunsaturated fatty acids. They contain
a hydratase that converts d-3-hydroxyacyl CoA into trans-D 2-enoyl CoA. How can this enzyme be
used to oxidize CoAs containing a cis double bond at an even-numbered carbon atom (e.g., the cis-
D 12 double bond of linoleate)? /3 marks
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4. An animal is fed stearic acid that is radioactively labeled with 14
C carbon. A liver biopsy reveals
the presence of 14
C-labeled glycogen. How is this possible in light of the fact that animals cannot
convert fats into carbohydrates? /2 marks
5. Suggest an explanation for the fact that the amount of glycogen in type I glycogen-storage
disease (von Gierke disease) is increased. /2 marks
6. Patients in shock will often suffer from lactic acidosis due to a deficiency of O2. Why does a lack
of O2 lead to lactic acid accumulation? One treatment for shock is to administer dichloroacetate,
which inhibits the kinase associated with the pyruvate dehydrogenase complex. What is the
biochemical rationale for this treatment? /2 marks
7. Name the α-ketoacid that is formed by transamination of each of the following amino acids:
/6 marks
(a) Alanine
(b) Aspartate
(c) Glutamate
(d) Leucine
(e) Phenylalanine
(f) Tyrosine
8. What is the yield of ATP when each of the following substrates is completely oxidized to CO2 by
a mammalian cell homogenate? Assume that glycolysis, the citric acid cycle, and oxidative
phosphorylation are fully active. /6 marks
(a) Pyruvate
(b) Lactate
(c) Fructose 1,6-bisphosphate
(d) Phosphoenolpyruvate
(e) Galactose
(f) Dihydroxyacetone phosphate
9. Glucose labeled with 14
C at C-1 is incubated with the glycolytic enzymes and necessary
cofactors. 2 marks
(a) What is the distribution of 14
C in the pyruvate that is formed? (Assume that the interconversion
of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate is very rapid compared with the
subsequent step.)
(b) If the specific activity of the glucose substrate is 10 mCi mM-1, what is the specific activity of
the pyruvate that is formed? /

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10. Which of the 20 amino acids can be synthesized directly from a common metabolic
intermediate by a transamination reaction? /3 marks
11. What are the likely consequences of a genetic disorder rendering fructose 1,6-bisphosphatase in
liver less sensitive to regulation by fructose 2,6-bisphosphate? /2 marks
12. What is the direction of each of the following reactions when the reactants are initially present
in equimolar amounts? Use the data given in the table below. /4 marks
13. What information do the ∆G° data given in Table 13.6 provide about the relative rates of
hydrolysis of pyrophosphate and acetyl phosphate? /1 marks
14. What is the structural feature common to ATP, FAD, NAD+, and CoA? /1 marks

4.
15. The following graph shows how the ∆G for the hydrolysis of ATP varies as a function of the
Mg2+
concentration (pMg = log 1/[Mg2+
]). /2 marks
(a) How does decreasing [Mg2+]
affect the ∆G of hydrolysis for ATP?
(b) How can you explain this effect?
16. The two basic mechanisms for the elongation of biomolecules are represented in the adjoining
illustration. In type 1, the activating group (X) is released from the growing chain. In type 2, the
activating group is released from the incoming unit as it is added to the growing chain. Indicate
whether each of the following biosynthesis is by means of a type 1 or a type 2 mechanism: /6
marks
(a) Glycogen synthesis
(b) Fatty acid synthesis
(c) C5 C10 C15 in cholesterol synthesis
(d) DNA synthesis
(e) RNA synthesis
(f) Protein synthesis
Examiner: Cleophas Rwemera Moderator: Dr. Mubamba Theodore