Chapter11Fall2005 - Chapter 19 Glycolysis Purpose...

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Chapter 19 - Glycolysis Purpose:  catabolism of glucose to provide ATPs and NADH molecules Also provides building blocks for anabolic pathways. Sequence of 10 enzyme-catalyzed reactions: glucose   pyruvate 2 ATPs and 2 NADH produced All enzymes (and reactions) are cytosolic. Net reaction: glucose + 2ADP + 2NAD +  +2P   2 pyruvate + 2ATP + 2NADH +2H +  +2H 2 O Can catabolize sugars other than glucose: e.g. fructose ----> 2 glyceraldehyde 3-phosphate e.g. lactose --> glucose + galactose galactose --> glucose 1-phosphate --> glucose 6-phosphate e.g. mannose ---> mannose 6-phosphate --> fructose 6-phosphate  Ten Steps of Glycolysis 1) glucose --> glucose 6-phosphate by hexokinase G = -8.0 kcal/mole Hexokinase also works on mannose and fructose at increased [ ]. Serves to trap glucose in the cell --> a phosphorylated molecule cannot leave 2) glucose 6-phosphate --> fructose 6-phosphate by glucose 6-phosphate isomerase Example of aldose--> ketose isomerization. Enzyme is very stereospecific. Reaction is near equilibrium in cell --> not a control point in glycolysis 3) fructose 6-phosphate --> fructose 1,6-bisphosphate by phosphofructokinase-1 (PFK-1) Reaction has   G = -5.3 kcal/mole and is metabolically irreversible. Represents the first committed step in glycolysis. 4) fructose 1,6-bisphosphate --> dihydroxyacetone phosphate + glyceraldehyde 3-phosphate by 
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Chapter11Fall2005 - Chapter 19 Glycolysis Purpose...

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