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chapter14 RKW - Lecture Connections 14 | Glucose...

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Lecture Connections 14 | Glucose Utilization and Biosynthesis © 2009 W. H. Freeman and Company
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CHAPTER 14 Glucose Utilization and Biosynthesis Harnessing energy from glucose via glycolysis Fermentation under anaerobic conditions Synthesis of glucose from simpler compounds: gluconeogenesis Oxidation of glucose in pentose phosphate pathway Key topics :
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Central Importance of Glucose Glucose is an excellent fuel Yields good amount of energy upon oxidation Can be efficiently stored in the polymeric form Many organisms and tissues can meet their energy needs on glucose only Glucose is a versatile biochemical precursor Bacteria can use glucose to build the carbon skeletons of: All the amino acids Membrane lipids Nucleotides in DNA and RNA Cofactors needed for the metabolism
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Four Major Pathways of Glucose Utilization When there’s plenty of excess energy, glucose can be stored in the polymeric form (starch, glycogen) Short-term energy needs are met by oxidation of glucose via glycolysis Pentose phosphate pathway generates NADPH that is used for detoxification, and for the biosynthesis of lipids and nucleotides Structural polysaccharides (e.g. in cell walls of bacteria, fungi, and plants) are derived from glucose
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Glycolysis: Importance Glycolysis is a sequence of enzyme-catalyzed reaction by which glucose is converted into pyruvate Pyruvate can be further aerobically oxidized Pyruvate can be used as a precursor in biosynthesis In the process, some of the oxidation free energy in captured by the synthesis of ATP and NADH Research of glycolysis played a large role in the development of modern biochemistry Understanding the role of coenzymes Discovery of the pivotal role of ATP Development of methods for enzyme purification
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Glycolysis: Overview In the evolution of life, glycolysis probably was one of the earliest energy-yielding pathways It developed before photosynthesis, when the atmosphere was still anaerobic Thus, the task upon early organisms was how to extract free energy from glucose anaerobically? The solution Activate it first by transferring couple of phosphates to it Collect energy later form the high-energy metabolites of the activated glucose
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Glycolysis: The Preparatory Phase
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Glycolysis: The Payoff Phase
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The Hexokinase Reaction The first step, phosphorylation of glucose, is catalyzed by hexokinase in eukaryotes, and by glucokinase in prokaryotes Nucleophilic oxygen at C6 of glucose attacks the last ( γ ) phosphorous of ATP Bound Mg ++ facilitates this process by stabilizing the negative charge in the transition state This process uses the energy of ATP
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Hexokinase Irreversible Reaction
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Reversible Reaction
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Mechanism of Phosphohexose Isomerase
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