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Unformatted text preview: they are mostly not interchangeable. Most enzymes will bind one or the other, but not both. Concentra7on of NAD+/NADH is about 10 7mes higher than NADP+/NADP. While NAD+/NADH is most o`en used in oxida7ve and catabolic pathways, NADP+/NADP is most o`en used in reduc7ve and anabolic pathways. Can you think of scenarios where it makes sense for cells to segregate the electron carriers used for catabolic and anabolic pathways? Vitamin B3 (Niacin) Toseland et al. BMC Bioinformatics 2005 6:283 Non ­oxida7ve phase of pentose phosphate network equilibrates the levels of compounds with different number of carbons according to the cell s par7cular needs. It s not as complicated as it looks. There are only two enzymes involved. Transketolase: C5 + C5 C3 + C7 Transaldolase: C3 + C7 C6 + C4 Transketolase: C4 + C5 C6 + C3 Overall: 3 C5 2 C6 + C3 C6 only: 6 C5 5 C6 Compare and contrast pentose phosphate pathway in cytosol and in chloroplast. The reac7ons that compose the pentose phosphate network have high plas7city and flexibility to meet the different demands of different 7ssues. Tissues with active pentose phosphate pathways: ____________________________________________________________________________________ Adrenal gland Gut epithelium, Bone marrow Liver Testes, Ovary Adipose tissue, Mammary gland Red blood cells (no nucleus) Steroid synthesis DNA synthesis Fatty acid and cholesterol synthesis Steroid synthesis Fatty acid synthesis Reduced glutathione to maintain Hb ____________________________________________________________________________________ No oxida7ve phase. Only nonoxida7ve reac7ons opera7ng in reverse. Both NADPH and nucleic acid synthesis are needed. Pentose phosphate cycle. Occurs when NADPH is needed, but glycolysis is not needed. Needs NADPH and ATP (for lipid synthesis, for example), but not nucleic acids. Transketolase mechanism (compare Transaldolase mechanism to pyruvate decarboxylase in (compare to aldolase in fermenta7on) glycolysis) What is the common chemical intermediate between reac7ons catalyzed by transketolase and transaldolase? Paradoxically, NADPH also plays an important role in the cell s ability to produce ROS for defense against pathogens Neutrophils and macrophages have specialized phagosomes that can kill bacteria. NADPH produced from PPP is used to generate ROS in phagosomes. NADPH is the reduced form of an electron carrier. Its job is to transfer electrons. How can it scavenge ROS in one system and generate ROS in another system? (Hint: look at the step ­wise single electron reduc7on of O2.) Thomas E. DeCoursey, Science Signaling Just like muta7on in hemoglobin that causes sickle ­cell anemia, muta7ons in G6P dehydrogenase are selected for protec7on against malaria. Plasmodium falciparum is harbored within red blood cells. Par7al G6P deficiency (heterozygous muta7on) results in reduced NADPH levels, leading to oxida7ve stress harmful to the pathogens. cdc.gov...
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