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Unit 3
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Glycolysis
Glycolysis is defined as a series of reactions that refers to the extraction of energy from a molecule of glucose by splitting it into two or three molecules of carbon. The broken-down molecules are also called pyruvates. (Kondoh, et, al. 2005). It is a process that is found in a number of organisms today.
Reaction
Glycolysis takes place in the cytosol of the cell, and it can be broken down into two major phases. These two phases are termed as Energy Requiring step and the energy releasing steps.
Energy Requiring Step
In this half of glycolysis, two adenosine triphosphate molecules are utilized in the phosphorylation of the glucose molecules. It involves a systematic procedure. In the first step, glycolysis is catalyzed by an enzyme called hexokinase which phosphorylates glucose by using ATP as a major source of phosphate. As a result, glucose 6 phosphate is produced that is the most reactive form of glucose. After that their glucose 6 phosphates is converted into an isomer named as Fructose 6 phosphate. Isomerase is the enzyme that facilitates this reaction. In the third step, phosphorylation of fructose 6 phosphate occurs which is then catalyzed by enzyme phosphofructokinase. (Lin, et, al. 2018). Fructose 1-6 bisphosphate is generated by the donation of high energy phosphate to fructose phosphate. Fructose 1-6 bisphosphate is then further desterilized by the addition of high energy phosphates taking into account that an enzyme aldolase cleaves 1-6 bisphosphate into two three carbon isomers named as, glyceraldehyde-3-phosphate and dihydroxyacetone-phosphate. In the last step, an isomerase transforms dihydroxyacetone phosphate into its isomer named as, glyceraldehyde-3-phosphate. It is the pathway in which there an investment of energy to ATP molecules, facilitating the breakdown of one glucose molecule. (Kondoh, et, al. 2005).
Energy Releasing Step
It is the second step of glycolysis in which energy is released in the form of 2 NADH molecules and 4 ATP molecules. This process involves the product of the first phase, taking into account that two three carbon sugar molecules will proceed where sufficient energy will be extracted in order to pay back two ATP molecules that are then used to produce high energy NADH molecules. (Kondoh, et, al. 2005). In this step, glyceraldehyde-3-phosphate is oxidized by the extraction of high energy molecules which are then picked by NAD + electron carriers leading to the formation of NADH. After that, another phosphate group is added. In the next step, phosphoglycerate kinase donates a high energy phosphate group to ADP, formulating ATP. The remaining phosphate groups in 3-phosphoglycerate produces 2-phosphoglycerate and then the enzyme Enolase allows 2 phosphoglycerates to lose water from its structure. In the end, glycolysis is catalyzed by the pyruvate kinase enzyme, formulating the ATP molecule. (Kim, et, al. 2005).
References
Kim, J. W., & Dang, C. V. (2005). Multifaceted roles of glycolytic enzymes. Trends in biochemical sciences, 30(3), 142-150.
Kondoh, H., Lleonart, M. E., Gil, J., Wang, J., Degan, P., Peters, G., ... & Beach, D. (2005). Glycolytic enzymes can modulate cellular life span. Cancer research, 65(1), 177-185.
Lin, P. P., Jaeger, A. J., Wu, T. Y., Xu, S. C., Lee, A. S., Gao, F., ... & Liao, J. C. (2018). Construction and evolution of an Escherichia coli strain relying on nonoxidative glycolysis for sugar catabolism. Proceedings of the National Academy of Sciences, 115(14), 3538-3546.
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