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Home | Glycolysis | Transition Reactions | Kreb's Cycle | Electron Transport Chain | Overview And Links


Glycolysis consists of two phases; glycolysis I and II. In glycolysis I, free (not used) energy is invested into the process of glycolysis. In glycolysis II, free energy is made and there is a pay off. This free energy comes in the form of ATP.

The process of glycolysis takes place in the cytoplasm of the animal cell. It's goal is to make ATP but also creates NADH+ which will become important in the electron transport chain to create more ATP during ATP synthase.

In glycolysis I, activation energy, or ATP, kick-starts the reactions. This ATP comes from a phosphate attaching to a ADP(Adenine Diphosphate) molecule, during the first phases of glycolysis. This ATP is used to add a phosphate to glucose (a six-carbon sugar made from six carbons and two phosphates) to form glucose 6-phosphate or just glucose. Another molecule of ATP is than used to turn fructose 6-phosphate into fructose 1,6-diphosphate. The molecule of fructose 1,6-diphosphate then will reorganize to form two molecules of three carbons and one phosphate called PGAL (glyceraldehydes 3-phosphate). These will be the activation energies for glycolysis II.

In glycolysis II, free energy is made in the form of ATP. The two PGAL that are made in Glycolysis I, are oxidized and the extra electrons are gained by NAD+ and it is reduced to NADH. The two molecules of PGAL, after loosing a phosphate each, is now two molecules of PGAP. After the PGAP molecules are made, ADP will help in removing a phosphate group from each PGAP to form two molecules of PGA and the phosphate removed will go with ADP to make ATP. The two PGA molecules are than oxidized, releasing water molecules and leaving two molecules of PEP. This is the last phase before the final product, Pyruvate, is made. With the help of another two molecules of ADP, like when making the two PGA molecules, the remaining phosphate will be removed from each PEP and used to make two more ATP and will leave behind a three-carbon molcule called Pyruvate, the primary ingredient for Transition Reactions.