lecture 9

lecture 9 - BIS 103 - 09 - Pentose Phosphate Pathway FIRST...

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BIS 103 - 09 - Pentose Phosphate Pathway Oxidative Phase NADPH production Pentose phosphate production ribulose-5-P xylulose-5-P ribose-5-P Non-oxidative Phase Transketolase and thiamine pyrophosphate (TPP) Transaldolase Interconversion of pentose-5-P to F6P and G3P Resynthesis of G6P from F6P and G3P Reducing Power Nucleotides for nucleic acid synthesis FIRST MIDTERM HIGH 195 LOW 40 MEDIAN 147
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We have discussed the production of ATP with glucose as the major source of metabolic energy. We have also seen how lipids and fatty acids can be a source of stored fuel and used to produce ATP. We will now turn to the generation of another type of metabolic energy - that is, reducing power . The currency of readily available reducing power in the cell is NADPH. The phosphoryl group on C-2 of one of the ribose units of NADPH distinguishes it from NADH (Lecture 2, slide 7).
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8 acetyl-CoA + 7 ATP + 14 NADPH + H + palmitate + CoA + 7 ADP + 7 Pi + 14 NADP + + 7 H 2 O During fatty acid synthesis, you saw that NADPH + H + was required Where does the cell get its NADPH + H + ? One source was the malic enzyme reaction: malate + NADP + pyruvate + CO 2 + NADPH + H + malic enzyme The major source for generating reducing power is the pentose phosphate pathway (PPP). Other reductive biosynthetic pathways also require NADPH.
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Remember that NADH is oxidized by the respiratory chain to generate ATP, whereas NADPH serves as an electron donor in reductive biosyntheses. The NAD/NADH linked enzymes oxidize and degrade substrates. The NADP/NADPH enzymes function primarily in reductive and biosynthetic reactions.
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The main functions of the pentose phosphate pathway (PPP) are to produce NADPH + H + and ribose-5-P. NADPH + H + is used in reductive biosynthetic reactions. Tissues that carry out extensive fatty acid synthesis (e.g. liver, adipose tissue, lactating mammary gland) or very extensive synthesis of cholesterol and steroid hormones (liver, adrenal gland, gonads) require NADPH from the PPP.
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NADPH + H + also is used to counteract the damaging effects of oxygen radicals. Erythrocytes and the cells of lens and cornea are directly exposed to oxygen and the damaging free radicals generated by oxygen. By maintaining a reducing atmosphere (a high ratio of NADPH/NADP + ), they can prevent damages to proteins, lipids and other sensitive molecules.
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and intestinal mucosa, use the ribose-5-phosphate to make nucleotides, RNA, DNA, and coenzymes such as ATP, NADH, FAD and CoA. In addition, the pathway operates to metabolize dietary pentose sugars, derived primarily from the digestion of nucleic acids. The role of the PPP is primarily anabolic rather than catabolic. Role of ribose-5-phosphate (R5P)
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This note was uploaded on 04/19/2008 for the course BIS 103 taught by Professor Abel during the Spring '08 term at UC Davis.

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lecture 9 - BIS 103 - 09 - Pentose Phosphate Pathway FIRST...

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