Biochemistry II/Chem 4420/Exam II/ 1997

3.  (10 points)Several of the reactions in glycolysis and the TCA cycle have positive )GE' values, yet the reactions are still driven towards the products. There are several different ways that can compensate for these standard state free energy values. Pick one of the following and discuss its effect on )G_rxn and give an example of a reaction in glycolysis or the TCA cycle where the effect you chose occurs. Be sure to show all equations that are relevant.

4.  (10 points) If glucose is labeled with ¹⁴C in the 1 position, where is the label in the oxaloacetate after one turn of the TCA cycle?

5.  (10 points) Why does citric acid cycle only operate when there is oxygen present? Be sure to include the regulatory mechanisms of the cycle in your discussion.

6.  (10 points) Malonate is an inhibitor of a TCA cycle enzyme because it is structurally similar to the substrate for that enzyme. How many ATP molecules could be generated under aerobic conditions from one molecule of pyruvate if malonate is present? The structure of malonate is shown below.

7.  (5 points) Anaplerotic reactions are those that result in replenishing intermediates in the TCA cycle. Give an example of an enzyme that catalyzes an anaplerotic reaction.

8.  (10 points) Explain why fatty acids with an even number of carbons can not be used to increase the concentration of TCA cycle intermediates and fatty acids with an odd number of carbons can be used to increase the concentration of TCA cycle intermediates.

9.  (15 points) Palmitoate that was uniformly labeled with tritium,(the tritium was in every possible position), was oxidized in liver mitochondrial cells. The amount of radioactivity in the isolated product (acetic acid, which was derived from acetyl CoA) contained only a small percentage of the original radioactivity (1/24).

Give the reactions involved in fatty acid metabolism (from palmitoate to acetyl-CoA).

Where is the rest of the radioactivity? Why is there such a small amount present in the acetic acid?

10.  (10 points) Many sea mammals drink no water, and have diets that are high in fat. In addition to using stored fat for insulation, they also use fat stores as a source of water.

How is fat used to make water? What reactions are involved?

How many liters of water can be obtained from the complete metabolism of 2 lbs of tripalmitoylglycerol?

11.  (10 points) Complete the following table: