U12_F08 - Unit 12 1 UNIT 12 PART A: THE PENTOSE PHOSPHATE...

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Unit 12 1 U NIT 12 P ART A: T HE P ENTOSE P HOSPHATE P ATHWAY P ART B: O XIDATIVE P HOSPHORYLATION P ART A: T HE P ENTOSE P HOSPHATE P ATHWAY The function of the pentose phosphate pathway is to generate pentose sugars and reducing power in the form of NADPH for use in biosynthetic pathways (for example, fatty acid synthesis). The metabolic state of the cell determines the relative amounts of NADPH and pentose sugars that are generated. The pathway is also used to convert pentose sugars to glucose which can then be metabolized for energy. Assignment: Nelson & Cox, pp. 558 - 563 (stop at section entitled (Wernicke- Korsakoff Syndrome. .."). Refer to the diagram that follows in addressing the following objectives. You are not required to memorize names or structures of intermediates. 1. Notice that the branch on the left is reversible and nonoxidative. It involves exchanges of 2- and 3-carbon fragments among intermediates. a. Considering the fact that no CO 2 is lost, how many moles of ribulose 5-P should be produced from 5 moles of glucose 6-P by these reactions? b. What types of enzymes catalyze the nonoxidative reactions (p. 560)?
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Unit 12 2 2. Notice that the branch on the right, labeled the oxidative or phosphogluconate branch, involves oxidation-reduction reactions and the loss of CO 2 . How many moles of ribulose 5-P are produced from 5 moles of glucose 6-P by these reactions? 3. Which pathway will be favored under the following conditions. Explain your answers. a. A condition in which more ribose 5-P is needed (as for nucleic acid synthesis) than NADPH. b. A condition in which more NADPH is needed (as for fatty acid synthesis) than ribose 5-phosphate. c. Which pathway (oxidative or nonoxidative) enables ribose 5- phosphate to be metabolized for energy ( i.e . for ATP)?
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Unit 12 3 OH HC O CH OP 2 glucose 6-P CH OP 2 O C O 6-phosphogluconolactone CH OP 2 O C O 6-phosphogluconate - CH OP 2 ribulose 5-P CH OH 2 O NADP + NADPH H O 2 NADP + NADPH CO 2 Oxidative (phosphogluconate) Branch Nonoxidative Branch (reversible) ribose 5-P
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Unit 12 4 P ART B: O XIDATIVE P HOSPHORYLATION Glycolysis and the citric acid cycle catalyze the oxidation of carbohydrates and fats to CO 2 , but the resulting electrons are left on the coenzymes NADH and FADH 2 . Oxidative phosphorylation is the process by which the energy
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This note was uploaded on 11/29/2010 for the course BIO 3300 taught by Professor Blankenship during the Fall '10 term at Cornell University (Engineering School).

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U12_F08 - Unit 12 1 UNIT 12 PART A: THE PENTOSE PHOSPHATE...

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