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Questions and Answers
What is the main purpose of the Pentose Phosphate Pathway?
Why is the Pentose Phosphate Pathway sometimes referred to as a 'shunt'?
Where does the Pentose Phosphate Pathway take place within the cell?
Which of the following is NOT a product of the Pentose Phosphate Pathway?
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What is the significance of Ribose 5-phosphate, a product of the Pentose Phosphate Pathway?
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In which phase of the Pentose Phosphate Pathway do irreversible oxidative reactions take place?
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What is the primary role of NADPH in the pentose phosphate pathway?
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Which of the following statements about the pentose phosphate pathway is correct?
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What is the primary function of the enzyme glutathione reductase in the detoxification process?
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Which of the following statements about the cytochrome P450 monooxygenase system is correct?
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What is the primary function of NADPH in phagocytosis by white blood cells?
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Which of the following statements correctly compares the roles of NADH and NADPH in cellular metabolism?
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Study Notes
Glucose 6-Phosphate Dehydrogenase (G6PD)
- Requires NADP+ as its coenzyme
- Insulin upregulates the expression of the gene for G6PD
Formation of Ribulose 5-Phosphate
- 6-Phosphogluconolactone is converted to ribulose 5-phosphate in two steps:
- Hydrolysis: 6-phosphogluconolactonase
- Oxidative decarboxylation: 6-phosphogluconate dehydrogenase
Reversible Non-Oxidative Reactions
- Occur in all cell types synthesizing nucleotides and nucleic acids
- Catalyze the inter-conversion of sugars containing three to seven carbons
- Permit ribulose 5-phosphate to be converted to:
- Ribose 5-phosphate (needed for nucleotide synthesis)
- Fructose 6-phosphate (intermediate of glycolysis)
- Glyceraldehyde 3-phosphate (intermediate of glycolysis)
NAD, NADP, and NADPH
- NADP+ differs from NAD+ by the presence of a phosphate group on one of the ribose units
- Ratio of NADP+/NADPH is approximately 0.1
- Ratio of NAD+/NADH is approximately 1000
- NADPH is used in reductive biosynthetic reactions
- NADH is used in oxidative catabolic reactions
Uses of NADPH
- Reductive biosynthesis
- Reduction of hydrogen peroxide (detoxification process)
- Cytochrome P450 monooxygenase system
- Phagocytosis by white blood cells
Pentose Phosphate Pathway (HMP Shunt)
- Alternative oxidative/non-oxidative pathway of glucose metabolism
- Occurs in the cytosol of cells
- Does not consume or produce ATP
- Begins with the glycolytic intermediate glucose 6-P
- Reconnects with glycolysis, producing glyceraldehyde 3-P and fructose 6-P
- Yields reducing potential in the form of NADPH for anabolic reactions
- Yields ribose 5-phosphate for nucleotide biosynthesis
Major Pathways Requiring NADPH
- Fatty acid synthesis
- Cholesterol synthesis
- Cytochrome P450 monooxygenase system
- Phagocytosis by white blood cells
Stages of Pentose Phosphate Pathway
- Oxidative phase (3 irreversible oxidative reactions)
- Non-oxidative phase (series of reversible sugar-phosphate interconversions)
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Description
Test your knowledge on the Pentose Phosphate Pathway (HMP Shunt) which is an alternative pathway of glucose metabolism that takes place in the cytosol of cells. Learn why it is called a shunt and how it reconnects with glycolysis.
