3500Ch15 - Glycolysis Where does it occur? 22 3 Stages: 1-...

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Glycolysis
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22 Where does it occur?
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3 Stages: 1- Conversion of glucose into fructose 1,6 – bisphosphate Traps glucose in the cell Creates a molecule that is cleaved into 2 – 3 carbon units. 2- Cleavage into 2- 3 carbon units.
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Hexokinase – traps glucose in the cell (G-6P is not a substrate for the transporter)
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77 Hexokinase reaction (Transfer RXN) Ø Mechanism : attack of C-6 hydroxyl oxygen of glucose on the γ-phosphorous of MgATP - displacing MgADP- Ø In general, most kinases require Mg2+ and use a similar mechanism Ø Glucose is FIRST phosphorylated when it comes into the cell!
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Large conformational change – this induced fit prevents hydrolysis of ATP in the
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99 Isozymes of hexokinase Isozymes - multiple forms of hexokinase occur in mammalian tissues and yeast Catalyze the same reaction , but have different Km values Hexokinases I, II, III are active at normal glucose concentrations (Km values ~10-6 to 10-4M) Hexokinase IV ( Glucokinase , Km ~10-2M) is active at higher glucose levels , allows the liver to respond to large increases in blood glucose I, II, and III are regulated, IV is not
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1010 Why would you want so many isoforms that can do the same job???
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Isomerization catalyzed by phosphoglucose isomerase
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A second phosphorylation done by PFK traps F-1, 6-BP This is reaction sets the pace for glycolysis – it is the key regulatory step!
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Cleavage into 2 interconvertable 3-carbon sugars
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1616 Aldolase (bond cleavage by lyase) Reaction is near-equilibrium, not a control point Had to be F1,6BP not G6P to get two equal trioses DAP GAP Go’ = + 23.8 kJ/mol What makes it favorable?
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Rapid and reversible 96% At equilibrium – so how does glycolysis proceed?
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Oxidation of GAP forms NADH and 1,3-BPG (a high phosphoryl-
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These are the two reactions that are catalyzed by glyceraldehyde 3-phosphate dehydrogenase
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ATP formation
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How many molecules of ATP have been formed? 2323
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2727 Pyruvate Kinase (PK) The second substrate-level phosphorylation Metabolically irreversible reaction , therefore a regulated step Regulation by allosteric modulators, by covalent modification, and by various hormones and nutrients
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2828
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This note was uploaded on 02/03/2011 for the course CHEM 3500 taught by Professor Staff during the Spring '08 term at Kennesaw.

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3500Ch15 - Glycolysis Where does it occur? 22 3 Stages: 1-...

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