1.  Biochemical taxonomy.



(a) Identify 6-phosphglucono-δ-lactone. _______

(b) Which reactions produce NADPH? _______

(c) Identify ribulose 5-phosphate. _______

(d) What reaction generates CO₂? _______

(e) Identify 6-phosphogluconate. _______

(f) Which reaction is catalyzed by phosphopentose isomerase? _______

(g) Identify ribose 5-phosphate _______

(h) Which reaction is catalyzed by lactonase? _______

(i) Identify glucose 6-phosphate. _______

(j) Which reaction is catalyzed by 6-phosphogluconate dehydrogenase? _______

(k) Which reaction is catalyzed by glucose 6-phosphate dehydrogenase? _______

2.  Phase shift. The pentose phosphate pathway is composed of two distinct phases. What are the two phases, and what are their roles? ✓ 6

3.  Designed to control or govern. What is the key regulatory enzyme in the pentose phosphate pathway, and what is its most prominent regulatory signal? ✓ 7

4.  No respiration. Glucose is normally completely oxidized to CO₂ in the mitochondria. Under what circumstance can glucose be completely oxidized to CO₂ in the cytoplasm? ✓ 6

5.  Watch your diet, Doctor. Noted psychiatrist Hannibal Lecter once remarked to FBI Agent Starling that he enjoyed liver with some fava beans and a nice Chianti. Why might this diet be dangerous for some people? ✓ 7

6.  Offal or awful? Liver and other organ meats contain large quantities of nucleic acids. In the course of digestion, RNA is hydrolyzed to ribose, among other chemicals. Explain how ribose can be used as a fuel. ✓ 6

7.  A required ATP. The metabolism of glucose 6-phosphate into ribose 5-phosphate by the joint efforts of the pentose phosphate pathway and glycolysis can be summarized by the following equation:



Which reaction requires the ATP?

8.  Tracing glucose. Glucose labeled with ¹⁴C at C-6 is added to a solution containing the enzymes and cofactors of the oxidative phase of the pentose phosphate pathway. What is the fate of the radioactive label?

9.  No redundancy. Why do deficiencies in glucose 6-phosphate dehydrogenase frequently present as anemia? ✓ 7

10.  Through the looking glass. Explain why the Calvin cycle and the pentose phosphate are almost mirror images of each other.

11.  Recurring decarboxylations. Which reaction in the citric acid cycle is most analogous to the oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate?

12.  You do what you can do. Red blood cells lack mitochondria. These cells process glucose to lactate, but they also generate CO₂. What is the purpose of producing lactate? How can red blood cells generate CO₂ if they lack mitochondria? ✓ 6

13.  Carbon shuffling. Ribose 5-phosphate labeled with ¹⁴C at C-1 is added to a solution containing transketolase, transaldolase, phosphopentose epimerase, phosphopentose isomerase, and glyceraldehyde 3-phosphate. What is the distribution of the radioactive label in the erythrose 4-phosphate and fructose 6-phosphate that are formed in this reaction mixture? ✓ 6

14.  Synthetic stoichiometries. What is the stoichiometry of the synthesis of (a) ribose 5-phosphate from glucose 6-phosphate without the concomitant generation of NADPH? (b) NADPH from glucose 6-phosphate without the concomitant formation of pentose sugars? ✓ 6

15.  Reductive power. What ratio of NADPH to NADP⁺ is required to sustain [GSH] = 10 mM and [GSSG] = 1 mM? Use the redox potentials given in Table 20.1.

16.  Catching carbons. Radioactive-labeling experiments can yield estimates of how much glucose 6-phosphate is metabolized by the pentose phosphate pathway and how much is metabolized by the combined action of glycolysis and the citric acid cycle. Suppose that you have samples of two different tissues as well as two radioactively labeled glucose samples, one with glucose labeled with ¹⁴C at C-1 and the other with glucose labeled with ¹⁴C at C-6. Design an experiment that would enable you to determine the relative activity of the aerobic metabolism of glucose compared with metabolism by the pentose phosphate pathway. ✓ 6