Biochemistry: Glycolysis

        Glycolysis is a series of reactions that extract energy from glucose by splitting it into two 3-carbon molecules called pyruvates. Glycolysis takes place in all organisms that preform cellular respiration, glycolysis is the first stage of cellular respiration. Glycolysis does not need oxygen organisms that do not use oxygen, anaerobic organisms use glycolysis. Glycolysis means the splitting of glucose. The beginning of the process occurs in the cytoplasm of the cell and yields a small amount of energy, which is measured in units of ATP. The other steps of this process occur in the mitochondria. This is an ongoing process because all the body's cells have a constant need for energy. Glycolysis is so important because in the cell, glucose is the main source of fuel for tissues in the body, so it is imperative that glycolysis is made possible.

        The process of glycolysis has ten steps, but can be broken down into to phases: the energy-requiring phase and the energy-releasing phase. In the energy-requiring phase is where the starting molecule of glucose gets rearranged, and two phosphate groups are attached to it. The modified sugar is made unstable by the phosphate groups, allowing it to split in half and make two phosphate-bearing 3-carbon sugars.  These steps come from ATP, where two ATP molecules get used up. ATP means Adenosine Tri-Phosphate. The 3-carbon sugars formed when the unstable sugar breaks down are different from each other. Only one glyceraldehyde-3-phosphate can enter the following step. The unfavorable sugar, DHAP, can be easily converted into the favorable one, meaning both finish the pathway in the end.
This diagram shows the detailed steps of the energy-requiring phase.

         The energy-releasing phase is where each 3-carbon sugar is converted into another 3-carbon molecule, pyruvate, through a series of reactions. In these reactions, two ATP molecules and one NADH molecule are made. NADH stands for Nicotinamide Adenine Dinucleotide.  Since this phase takes place two times, once for each of the two 3-carbon sugars, it makes four ATP and two NADH overall. Glycolysis converts one 6-carbon molecule of glucose into two 3-carbon molecules of pyruvate. The net products of this process are two molecules of ATP, because four ATP molecules are produced yet two are used up in the process, and two molecules of NADH.
This diagram shows both the energy-requiring phase and the energy-releasing phase.



Sources and Pictures: https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/glycolysis/a/glycolysis

Video Describing Glycolysis: https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/glycolysis/v/glycolysis