Download Bio302 Biochemistry II

Bio302 Biochemistry II
Final Examination, June 7, 2005
Please answer all the questions, each 10 points. Good luck!
Question 1: When O2 is aded to an anaerobic suspension of cells consuming glucose
at a high rate, the rate of glucose cosumption declines dramatically as the O2 is used
up, and accumulation of lactate ceases. This effect (called Pasteur effect) is
characteristic of most cells capable of both aerobic ad unaerobic glucose catabolism.
Answer the questions below and relate to the action of the specific enzymes involved
in this process.
a) Why does the presence of O2 decrease the rate of glucose consumption?
b) Why does the accumulation of lactate cease after O2 is added?
Question 2: Acetyl-CoA carboxylase is the principal regulation point in the
biosynthesis of fatty acids. The enzyme exists in two interconvertible forms that differ
markedly in their activities: an inactive protomer to an active filamentous polymer.
Citrate and isocitrate bind to the filamentous form, and palmitoyl-CoA binds
preferentially to the protomer. Explain how this property is consistent with the
regulatory role of acetyl-coA carboxylase in the biosynthesis of fatty acids.
Question 3: Glycogen phosphorylase is the key enzyme in glycogen breakdown. The
figure below shows different forms of this enzyme.
A: Using the figure explain and discuss the two primary control mechanisms which
acts to control tightly the activity of this enzyme in muscle.
B: Which are the active forms of muscle phosphorylase? Which form requires high
leves of AMP to be regulated? Which convrsions antagonize by ATP ad glucose-6phosphate?
Question 4: What are the similarities between fatty acid synthesis and degredation?
Discuss. What are the similarities of fatty acid synthesis and protein synthesis?
Question 5. How is pyrophosphate formation is important in chemistry? Give two
examples.
Question 6: Explain the terms or processes given below:
a)Thermogenesis; b) Homolytic cleavage; c) Chemiosmotic hypothesis;
d)Fermentation;
e) Anaplerotic reactions;
Question 7: What ratio of NADPH to NADP+ is required to sustain [GST]= 10 mM
and [GSSG]= 1 mM (reduced gluthathione and oxidized gluthathione, respectively) at
25oC? (Use the redox potentials given in Table 1. At this temperature RxT=1.36
kcal/mol).