Pentose Phosphate Pathway
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| What are two different names for the pentose phosphate pathway? | Hexose monophosphate pathway or 6-phosphogluconate pathway
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| Where in the cell does the pentose phosphate pathway occur? | In the cytosol
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| In which organs does the pentose phosphate pathway take place and what does the created NADPH provide for in each? | The liver, mammary glands, and adipose tissue (FA synthesis) as well as the adrenal cortex, testes, and ovaries (synthesis of steroid hormones), Erythrocytes (glutathione reduction) and WBC/Macrophages (phagocytosis).
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| What is the pentose phosphate pathway? | An alternative method for glucose metabolism, it does NOT create energy
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| What are the important products of the pentose phosphate pathway? | Pentoses, NADPH, and H+
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| Describe the oxidative phase of the pentose phosphate pathway. | 1) Oxidative phase = irreversible reactions, NADPH and pentose produced, used when nucleotide biosynthesis must take place, enzymes are dehydrogenases.
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| Describe the NonOxidative phase of the pentose phosphate pathway. | Nonoxidative phase = reversible rxns, occur when pentoses arent req'd by cells but glycolytic intermediates are, involves interconversion of sugars resulting in the formation of glycolytic intermediates, enzymes are transketolase (TPP) and transaldolase.
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| Describe the steps in the oxidative phase of the pentose phosphate pathway. | Glucose-6-phosphate -> 6-phosphogluconolactone via G6PD (releasing NADPH and H+), which is then -> 6-phosphogluconate and then-> Ribulose-5-phosphate via 6-phosphogluconate dehydrogenase (releasing NADPH, H+, and CO2)
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| What is the regulatory enzyme of the pentose phosphate pathway? | G6PD
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| Describe the steps in the nonoxidative phase of the pentose phosphate pathway. | If 3 mols of G6P -> 3 mols of Ribulose5P, Ribulose5P -> Ribose5P (via isomerase) + 2 Xyulose5P (via epimerase) -> 2 mols of F6P and 1 Glyceraldehyde-3P (glycolytic intermediates) via transketolase and transaldolase.
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| What is the coenzyme of Transketolase? | TPP (Thiamine)
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| What can be used as a laboratory test to diagnose nutritional thiamine deficiency? | Transketolase activity in RBCs
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| What is Ribose-5-Phosphate required for? | Nucleotide synthesis
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| What are the uses of NADPH? | synthesis of fatty acids, synthesis of steroid hormones, cytochrome p450 system, reduction and detoxification of H2O2, and synthesis of Nitric oxide.
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| What does G6PD deficiency lead to? | Decreased cellular pool of GSH leading to a decrease in detoxification of free radicals/peroxides in cells (accumulate, damage the membrane resulting in hemolysis) as well as protein denaturation (insoluble masses = Heinz bodies)
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| What is the significance of reduce glutathione (GSH)? | It is the major antioxidant in RBCs and it is required for maintenance of SH groups in proteins.
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| In what cell type is G6PD deficiency the most severe? | RBCs because the pentose phosphate pathway is the only means of NADPH generation.
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| What precipitating factors lead to G6PD deficiency? | Infections, oxidant drugs (sulfa drugs, primaquine) and Fava Beans (yes, the vegetable).
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| What is G6PD A- deficiency result in? | A moderate form of the disease, enough young RBCs have sufficient levels of enzyme so they are normally ok but issues arise when exposed to a precipitating factor.
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