Metabolism: Pentose phosphate pathway
Hand-out for the CBT – version May 2012
1. Which of the following compounds are products of the pentose phosphate pathway?
o NADPH o glycerate 3-phosphate o CO2 o ribulose 5-phosphate o sedoheptulose 7-phosphate
2. The first four reactions of the pentose phosphate pathway form the oxidative phase. The following questions deal with these reactions.
A. What are the names of these compounds?
B. During which reactions are CO2 and NADPH produced?
C. What reaction is catalyzed by phosphopentose isomerase?
D. Which compound can be a group acceptor in the transketolase reaction?
3. The following questions are about glucose 6-phosphate dehydrogenase.
A. Is 6-phosphogluconate one of its products?
B. Is it regulated by the availability of NAD+?
C. Does is contain thiamine pyrophosphate as a cofactor?
D. A committed step is an effectively irreversible enzymatic reaction that occurs in metabolic reactions during the biosynthesis of some molecules. Does glucose 6-phosphate dehydrogenase catalyse the committed step in the pentose phosphate pathway?
E. Is it important in the metabolism of glutathione in erythrocytes?
4. The pentose phosphate pathway has a nonoxidative branch. What reactions does it include?
5. The liver synthesizes fatty acids and lipids for export to other tissues. What activity do you expect the pentose phosphate pathway to have in the liver?
o Low, because this synthesis needs ATP and pentoses as a source o Low, because no reductive force is needed o High, because this is reductive biosynthesis o High, because the conversion of sugars is required 6. A. What similarities have transaldose and transketolase?
o They both require thiamine pyrophosphate o They both form a Schiff base with the substrate o They use the same type of monosaccharide as a group donor o They both form a covalent addition compound with the donor substrate
B. What type of monosaccharide do transaldose and transketolase use as a group donor?
7. Which enzyme catalyzes the rate limiting step in the pentose phosphate pathway?
o lactonase o transaldolase o transketolase o glucose 6-phosphate dehydrogenase o 6-phosphogluconate dehydrogenase
8. A cell is in a metabolic situation where it requires much more NADPH than ribose 5-phosphate. Also required is the complete oxidation of glucose 6-phosphate to CO2.
Which of the following conversions will take place?
o ribose 5-P fructose 6-P o fructose 6-P glucose 6-P o ribose 5-P glyceraldehyde 3-P o glyceraldehyde 3-P pyruvate o glyceraldehyde 3-P ribose 5-P o glucose 6-P ribulose 5-P
9. The pentose phosphate pathway (PPP) and the Calvin cycle are mirror images of each other. What four compounds does the Calvin cycle use and the PPP form?
1)
2)
3)
4)
10. The first four reactions of the pentose phosphate pathway form the oxidative phase. In drug- induced hemolytic anemia the enzyme for one of these reactions is deficient. For which reaction? (Indicate the reaction in the figure with question 2.)
11. The following questions are about reduced glutathione.
A. What components does it contain?
B. Does is keep the cysteine residues of proteins in their reduced states?
C. Is it generated from oxidized glutathione by glutathione reductase?
D. Does it react with hydrogen peroxide and organic peroxides?
E. In glucose 6-phosphate dehydrogenase deficiency, is it increased or decreased relative to oxidized glutathione?