Molecular Biology & Biochemistry - BIOL 8 TAKE-HOME  EXAM 3 - April 23, 1997 NAME: This is a take-home exam. Your final product must be turned in by the beginning of class, 9:30 p.m., Tuesday, April 29. It must be typed/printed. Handwritten work will be accepted for diagrams and problem solving portions ONLY. Show all work for possible partial credit.

You must work independently. You may, however, request assistance from the instructor. You may also, if you are enrolled in the appropriate class, get help from the Humanities Center or similar tutorial assistance to improve the written presentation. The intent here is that you are responsible for the content.

Please try to focus your answers as much as possible. Aim for brief & complete. Remember that answers that do not relate to the question may cost credit for errors, but can not earn any credit since they do not answer the question!! Thus, it is to your advantage to refrain from adding extraneous information. Please do NOT just copy from a book. Note that often a book is not answering precisely the question that you are supposed to be addressing!

1. [20 pts] Please refer to Table 19-3 in your text. For the following components, explain the effect on the rate of glycolysis (as a whole --net pyruvate production) if their concentration were to increase or decrease. Treat each as a separate event, that is, this is a MULTI-PART question! [For each component, assume that the change is significant - obviously, the absolute quantities will vary among the components.] Explain your logic.

a. glucose b. glucose-6-P c. fructose 1,6 bisphosphate d. PEP e. pyruvate

2. [5 pts] Why do you think that fructose 2,6 bisphosphate, a metabolite in glycolysis, is not in Table 19-3?

3. [5 pts] Explain the huge discrepancy between 1,3-bisphosphoglycerate concentration and that of 2,3-bisphosphoglycerate. (Relate function and concentration.)

4. [5 pts] Certain muscle wasting diseases are caused by malfunctioning mitochondria. What effect on muscle function would you expect from loss of functioning mitochondria? How would muscle get energy? Would a person with such a disease have to eat more, less, or the same amount of food in order to do work? Explain.

5. [10 pts] The intravenous infusion of fructose into healthy volunteers leads to a two- to five-fold increase in the level of lactate in the blood, a far greater increase than that observed following the infusion of the same amount of glucose.

a. Why is glycolysis more rapid following the infusion of fructose?

b. Fructose has been used in place of glucose for intravenous feeding. Why is this use of fructose unwise?

c. So, is fruit sugar better for us than table sugar? Explain your answer.

6. [10 pts] Explain the allosteric and the hormonal regulation of phosphofructokinase. Why is this so important? (Do not forget to mention roles of ATP, AMP, citrate, and pH, and how they relate to metabolic rates). DO NOT COPY FROM THE BOOK - remember, I have a copy, too!

7. [10 pts] A non-spontaneous reaction can be driven by a spontaneous reaction. Choose four mechanisms by which such reactions can be coupled. For each, briefly explain the mechanism; give one specific example.

8. [5 pts] Table 20-1 indicates that the succinate --> fumarate conversion has a DG^o’~0. Is it true that no energy is gained by this step? What is the significance of this step in the TCA cycle? Explain

9. [5 pts] Draw a. a-d-galactopyranose b. b-d-ribofuranose c. a-l-mannopyranose

d. b-d-sorbose e. b-d-galactopyranose rotated 180^o through the plane of the paper

10. [15 pts] What would be the effect of an analog of oxaloacetate which can bind as oxaloacetate but can not be hydrolyzed? a) on the TCA cycle, b) on glycolysis c) on acetyl CoA binding to citrate synthase

11.[10 pts] You are an investigator, studying a eukaryote to whom you feed glucose labeled in all of its carbon atoms. How many rounds of the Krebs cycle are required for the complete hydrolysis of a molecule of glucose to CO₂ + H₂O? Explain. Be sure you keep track of the labeled C’s.