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Glycolysis

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The process of glycolysis.

Glycolysis is a key chemical reaction that occurs in both aerobic and anaerobic respiration, but does not require oxygen.[1] In this reaction, glucose is converted into two molecules of pyruvic acid and four adenosine triphosphate molecules.[2] These ATP molecules contain energy.[3] Since this process uses two ATPs, the cell gains a total of two ATP molecules during glycolysis.[2] Glycolysis consists of nine steps. First, a phosphate group is added to the glucose molecule using an enzyme called hexokinase to form glucose-6-phosphate. In the second step, the enzyme phosphoglucose isomerase reorganizes the molecule and changes its structure from a six-membered ring to a five-membered ring. Next, the molecule, now fructose-6-phosphate gains another phosphate group with the help of phosphofructokinase, creating fructose- 1,6-bisphosphate. During the fourth step of glycolysis, another enzyme, aldolase, breaks the fructose- 1,6-biphosphate into two carbon-3 molecules.[4]

In the next step of glycolysis, the carbon-3 molecules are oxidized by an NAD molecule, which takes a hydrogen atom from the carbon-3. In addition, the carbon-3 molecules receive another phosphate group with glyceraldehyde-3-phosphate dehydrogenase serving as a catalyst, resulting in 1,3 bisphoglycerate. After this the enzyme phosphoglycerate kinase is involved in a reaction in which an ADP molecule receives a phosphate group from each 1,3 bisphoglycerate molecule, forming two ATPs and two 3 phosphoglycerate molecules. An enzyme called phosphoglycerate mutase then rearranges the placement of the phosphates on the 3 phosphoglycerate to make 2 phosphoglycerate. Next, enolase takes a water molecule from the 2 phosphoglycerate and forms the product phosphoenolpyruvate. Finally, the enzyme pyruvate kinase catalyzes a reaction that moves a phosphate group from the phosphoenolpyruvate molecules to ADP molecules, creating two more ATPs and pyruvic acid, the final products of glycolysis.[5]

References

  1. Nave, Carl. Cellular Respiration HyperPhysics. Web. Accessed on November 19, 2015.
  2. 2.0 2.1 Wile, Jay L., and Shannon, Marilyn M. The Human Body: Fearfully and Wonderfully Made!. Cincinnati: Apologia Educational Ministries, Inc., 2001. 147-148. Print.
  3. Wile, Jay L., and Shannon, Marilyn M. The Human Body: Fearfully and Wonderfully Made!. Cincinnati: Apologia Educational Ministries, Inc., 2001. 145. Print.
  4. SparkNotes Editors.Glycolysis Stage 1: Glucose Breakdown SparkNotes. Web. Accessed on November 19, 2015.
  5. SparkNotes Editors.Glycolysis Stage 2: Conversion to Pyruvate SparkNotes. Web. Accessed on November 19, 2015.