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Glycolysis

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Aisha Alawi

on 12 April 2013

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Transcript of Glycolysis

The First Stage of Cellular Respiration Glycolysis THE BEGINNING END RESULT: The whole process begins with glucose, a monosaccharide, or simple sugar, that contains stored energy. When broken down in glycolysis, the glucose molecule undergoes a series of reactions that break it down into two 3 carbon molecules of pyruvate. Some of the stored energy is released as ATP as well (a form of energy that can be utilized by the cell). In this first step, the phosphorylase enzyme hexokinase removes a phosphate group from an ATP molecule and attaches it to glucose. This results in a glucose 6 phosphate molecule and ADP. Step 1: In the enzyme phosphoglucose isomerase, the chemical structure of glucose 6 phosphate is altered from an aldose to the ketose sugar fructose 6 phosphate. This is done to create a more symmetrical molecule that can be later split into two identical parts. Step 2: Now more symmetrical, the molecule is again phosphorylated using a phosphorylase enzyme and ATP. The only difference is that the enzyme used in this step is phosphofructokinase. After the phosphorylation takes place, fructose 1,6 diphosphate(bisphosphate) is produced along with ADP. Step 3: 2 ATP are used Step 4: It is in this step that the sugar is split. With the special enzyme aldoase, fructose 1,6 diphosphate is split into two 3 carbon molecules: dihydroxyacetone phosphate (DHAP) and phosphoglyceraldehyde (PGAL). Step 5: Using the triose phosphate isomerase enzyme, dihydroxyacetone phosphate is isomerized into a phosphoglyceraldehyde molecule, resulting in the presence of two molecules of phosphoglyceraldehyde. Step 6: A dehydrogenase enzyme is seen in this step for the first time. Using it, a hydrogen is removed from phosphoglyceraldehyde and used to reduce NAD+. In this step, an inorganic phosphate is added to phosphoglyceraldehyde as well. The result is a molecule of diphosphoglycerate (DPGA) and the hydrogen carrier NADH. Step 7: Here, energy is obtained for the first time in the form of ATP. The phosphorylase enzyme phosphoglycerate kinase removes a phosphate group from diphosphoglycerate and phosphorylates a molecule of ADP. This results in 3-phosphoglycerate (3PGA) and a molecule of ATP. Step 8: The structure of 3-phosphoglycerate is changed by the enzyme phosphoglecerate mutase into its isomer, 2-phosphoglycerate. In the end: Step 9: In this step, the special enzyme enolase removes a water molecule from 2-phosphoglycerate, producing the phosphoenolpyruvate molecule and water. Step 10: Aisha Alawi The phosphorylation of glucose provides a handle onto which enzymes can hold on to, destabilizes the molecule so it can react further, and changes the structure so glucose does not diffuse out of the cell and back into the bloodstream. NOTE: Steps 5 to 10 each happen twice, once for every molecule of PGAL (phosphoglyceraldehyde). The ATP here is made through substrate level phosphorylation. In this last step, ADP is phosphorylated once more into ATP. This is done with the aid of phosphorylase enzyme pyruvate kinase, which removes a phosphate group from phosphenolpyruvate and attaches it to ADP. Aside from ATP, the 3-carbon molecule pyruvate is produced as well. The ATP here is made through substrate level phosphorylation. 2 NADH are made (one for each phosphoglyceraldehyde) 4 ATP produced (two for each phosphoglyceraldehyde) 2 pyruvate are formed (one for each phosphoglyceraldehyde) BUT ...
2 ATP were used in the beginning so the net total of ATP is only 2 AND
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