13 - Carb Pathways.pptx - Glucose In animals and vascular...

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Glucose 2 In animals and vascular plants, glucose has three major fates: it may be stored (as a polysaccharide or as sucrose); oxidized to a three-carbon compound (pyruvate) via glycolysis to provide ATP and metabolic intermediates; or oxidized via the pentose phosphate (phosphogluconate) pathway to yield ribose 5-phosphate for nucleic acid synthesis and NADPH for reductive biosynthetic processes.
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Glucose 3 Organisms that do not have access to glucose from other sources must make it. Photosynthetic organisms make glucose by first reducing atmospheric CO2 to trioses, then converting the trioses to glucose. Nonphotosynthetic cells make glucose from simpler three- and four-carbon precursors by the process of gluconeogenesis, effectively reversing glycolysis in a pathway that uses many of the glycolytic enzymes. Found in nearly every living cell. For some tissues (such as brain, kidney, medulla, and rapidly contracting skeletal muscles) and for some cells (such as erythrocytes and sperm cells), glucose is the only source of metabolic energy.
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Cellular Respiration 4 Cellular respiration occurs in three major stages. In the first , organic fuel molecules – glucose, fatty acids, and some amino acids – are oxidized to yield two-carbon fragments in the form of the acetyl group of acetyl-coenzyme A (acetyl-CoA).
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Cellular Respiration 5 In the second stage , the acetyl groups are fed into the citric acid cycle, which enzymatically oxidizes them to CO 2 The energy released is conserved in the reduced electron carriers NADH and FADH 2 .
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Cellular Respiration 6 In the third stage of respiration, these reduced coenzymes are themselves oxidized, giving up protons (H + ) and electrons. The electrons are transferred to O 2 – the final electron acceptor – via a chain of electron-carrying molecules known as the respiratory chain.
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Glycolysis 7 Glycolysis is also called the Embden-Meyerhof (or Warburg) Pathway Essentially all cells carry out glycolysis Ten reactions – essentially the same in all cells but with different rates Two phases: First phase converts glucose to two glyceraldehyde 3- phosphate (G-3-P) Second phase produces two pyruvates Products are pyruvate, ATP and NADH
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Glycolysis: Phase 1 8 1 6
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Glycolysis: Phase 2 9 1,6 1,6
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Glycolysis 10 Overall balance sheet (keep in mind that each molecule of glucose yields two molecules of pyruvate): Glucose + 2 ATP + 2 NAD + + 4 ADP + 2 Pi → 2 pyruvate + 2 ADP + 2 NADH + 2 H + + 4 ATP + 2 H 2 O Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 pyruvate + 2 NADH + 2 H + + 2 ATP + 2 H 2 O Glycolysis is exergonic with a ΔG°’ of -74 kJ/mol.
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Free-energy Changes of Glycolytic Reaction in Erythrocytes 11 Standard state ΔG’° values are scattered, with both plus and minus values and no apparent pattern
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Free-energy Changes of Glycolytic Reaction in Erythrocytes 12 Steady-state concentrations of glycolytic metabolites in Erythrocytes
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Free-energy Changes of Glycolytic Reaction in Erythrocytes 13 The plot of ΔG values in cells is more revealing:
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