Lecture_4 - Lecture 4 Glycolysis II 2 ATPs formed in...

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Lecture 4: Glycolysis II
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2 ATPs formed in conversion of glucose to pyruvate Glucose + 2 P i + 2 ADP + 2 NAD + 2 pyruvate + 2 ATP + 2 NADH + 2H + + 2 H 2 O Net reaction Energy released in anaerobic conversion of glucose to pyruvate -96 kJ/mol (-23 kcal/mol) The conversion of glucose to pyruvate cannot keep proceeding because redox balance has not been maintained
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Redox must be maintained Glyceraldehyde 3-phosphate dehydrogenase generates ATP but at the expense of NAD + Limited amounts of NAD + in the cell NAD + derived from vitamin niacin (dietary requirement in humans) NAD + must be regenerated for glycolysis to proceed
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Re-dox balance steps generation and consumption of NADH Ethanol or lactate
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3 fates of pyruvate Ethanol Lactate Carbon dioxide No oxygen, fermentation Oxygen Citric acid cycle Electron transport chain
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Ethanol from pyruvate Yeast and other microorganisms Step 1: decarboxylation of pyruvate Catalyzed by pyruvate decarboxylase Requires coenzyme thiamine pyrophosphate Derived from vitamin thiamine (B1) Step 2: reduction of acetaldehyde to ethanol by NADH Catayzed by alcohol dehydrogenase Regenerates NAD +
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Alcoholic fermentation Glucose + 2 P i + 2 ADP + 2 H + 2 ethanol + 2 CO 2 + 2 ATP + 2 H 2 O No net oxidation-reduction in the conversion of glucose into ethanol (NADH generated and then consumed)
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oxidation reduction No net oxidation-reduction
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Lactate from pyruvate Occurs in a variety of microorganisms (lactic acid fermentation ) and in higher organisms when oxygen is limiting (muscle in intense exercise) Pyruvate is reduced by NADH to form lactate Catalyzed by lactate dehydrogenase
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Lactic acid fermentation Glucose + 2 P i + 2 ADP 2 lactate + 2 ATP + 2 H 2 O No net oxidation-reduction
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CO 2 from pyruvate Oxidative decarboxylation of pyruvate to acetyl coenzyme A (acetyl CoA) Entry point to Citric acid cycle and the electron transport chain Much more energy is extracted from glucose Formed inside mitochondria Aerobic reaction Catalyzed by pyruvate dehydrogenase NADH transfers its electrons to O 2 in electron transport chain Pyruvate + NAD + + CoA acetyl CoA + CO 2 + NADH
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Obligate anaerobe – cannot survive in the presence of oxygen Why are the pathways that do not yield much energy used so often?
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Fructose and galactose (monosaccharides other than glucose) No catabolic pathways for metabolizing fructose and galactose Can be funneled into glycolytic pathway By converting them to a metabolite of glucose
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Entry points in glycolysis for galactose and fructose
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Fructose – 2 pathways Fructose 1-phosphate pathway (liver) Step 1: fructose to fructose 1-phosphate by
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