Biochemistry Multiple Choice Questions on “Pentose Phosphate Pathway of Glucose Oxidation”.
1. In the pentose phosphate pathway, the major products are ____________
A. Ribulose and NADPH
B. Ribulose and NADH
C. Ribulose and NAD+
D. Ribulose and ATP
Answer: A
Clarification: The products formed are pentose, ribulose and NADPH.
2. What is the first reaction of the pentose phosphate pathway?
A. Oxidation of glucose 6-phosphate to 6-phosphoglucono-δ-lactone
B. Oxidation of 6-phosphogluconate to ketopentose ribulose 5-phosphate
C. Reduction of 6-phosphoglucono-δ-lactone to glucose 6-phosphate
D. Reduction of ketopentose ribulose 5-phosphate to 6-phosphogluconate
Answer: A
Clarification: The first reaction of the pentose phosphate pathway is the oxidation of glucose 6-phosphate to 6-phosphoglucono-δ-lactone by glucose 6-phosphate dehydrogenase.
3. Which of the following statements is correct about oxidative pentose phosphate pathway?
A. It generates NADH
B. It oxidizes NADPH to NADP+
C. The pathway supplies ribose 5-phosphate and NADPH in the quantities the cell requires
D. Glucose 6-phosphatase catalyzes the rate limiting reaction of the pathway
Answer: C
Clarification: Oxidative pentose phosphate pathway supplies ribose 5-phosphate and NADPH in the quantities the cell requires. It reduces NADP+ to NADPH.
4. Which one out of the following enzymes acts in the pentose phosphate pathway?
A. Aldolase
B. Glycogen phosphorylase
C. Pyruvate kinase
D. 6-phosphogluconate dehydrogenase
Answer: D
Clarification: The first reaction in pentose phosphate pathway is catalyzed by 6-phosphogluconate dehydrogenase.
5. Oxidation of 3 molecules of glucose by pentose phosphate pathway results in the production of ____________
A. 3 molecules of pentose, 6 molecules of NADPH and 3 molecules of CO2
B. 4 molecules of pentose, 6 molecules of NADPH and 3 molecules of CO2
C. 4 molecules of pentose, 3 molecules of NADPH and 3 molecules of CO2
D. 3 molecules of pentose, 4 molecules of NADPH and 3 molecules of CO2
Answer: A
Clarification: Glucose 6-phosphate + 2NADP+ + H2O → ribose 5-phosphate + CO2 + 2NADPH + 2H+.
6. What is the main function of the pentose phosphate pathway?
A. Supply NADP+
B. Supply NADH
C. Supply energy
D. Supply pentoses and NADPH
Answer: D
Clarification: The main function of pentose phosphate pathway is to supply pentoses to NADPH.
7. Which one of the following statements is correct about the pentose phosphate pathway?
A. It generates 6 moles of CO2 for each mole of glucose consumed
B. It generates 38 mol of ATP per mole of glucose consumed
C. It is a reductive pathway that consumes NADH
D. Present in plants but not in animals
Answer: A
Clarification: There is the continued production of NADPH and converting glucose 6-phosphate (in six cycles) to CO2.
8. Which of the following statements is correct about the reductive pentose phosphate pathway?
A. It is not reversible
B. Transketolase transfers 3 carbon units
C. Transaldose transfers 2 carbon units
D. Pentoses can provide glycolytic intermediates
Answer: D
Clarification: It is reversible, transketolase transfers 2 carbon units and transaldose transfers 3 carbon units.
9. The use of NADPH generated from pentose phosphate pathway cannot be ____________
A. oxidized in the electron transport chain to provide 38 ATPs
B. Used for the synthesis of fatty acids
C. Used for the macrophageal functions
D. Used for steroid synthesis
Answer: A
Clarification: NADPH cannot be oxidized in the electron transport chain to provide 38 ATPs.
10. Conversion of xylulose 5-phosphate to ribulose 5-phosphate is catalyzed by ___________
A. Phosphopentose epimerase
B. Transaldolase
C. Transketolase
D. Phosphopentose isomerase
Answer: A
Clarification: Conversion of xylulose 5-phosphate to ribulose 5-phosphate is catalyzed by epimerase.
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