Lecture21a - Glycolysis Preparatory phase The first five...

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Glycolysis Glucose Preparatory phase The first five steps are regarded as the preparatory (or investment) phase since they consume energy to convert the glucose into two three-carbon sugar phosphates ( G3P ). The first step in glycolysis is phosphorylation of glucose by a family of enzymes called hexokinase to form glucose-6-phosphate. This reaction consumes ATP, but it acts to keep the glucose concentration low, promoting continuous transport of glucose into the cell through the plasma membrane transporters. In addition, it blocks the glucose from leaking out - the cell lacks transporters for glucose 6-phosphate. Glucose may alternatively be from the hydrolysis of intracellular starch or glycogen. Glucose-6- Phosphate ATP ADP Hexokinase a transferase
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Glycolysis Glucose-6-phosphate is then rearranged into fructose-6-phosphate by glucose phosphate isomerase. Fructose can also enter the glycolytic pathway by phosphorylation at this point. The change in structure is an isomerization, in which the glucose-6-phosphate has been converted to fructose 6-phosphate. The reaction requires an enzyme, phosphohexose isomerase, to proceed. This reaction is freely reversible under normal cell conditions. However, it is often driven forward because of a low concentration of fructose 6-phosphate, which is constantly consumed during the next step of glycolysis. Under conditions of high fructose 6-
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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Lecture21a - Glycolysis Preparatory phase The first five...

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