Release of energy from glucose
Glycolysis is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of ATP. Glucose is the starting material and two molecules of pyruvate are the end products of the pathway. Subcellular site of the pathway is the cytosol. Glycolysis is a linear pathway of ten enzyme mediated steps.
Phases of glycolysis
Pathway has two phases: Energy investment phase and energy generation phase. Energy investment phase is also called preparatory phase and consists of first five steps. Here the end product is glyceraldehyde - 3 – phosphate. Energy generation phase is also known as payoff phase and consists of last five steps and end products are two pyruvate molecules.
Energy yield from the pathway
It can occur in presence or absence of oxygen. Altogether there are ten steps involved and in aerobic glycolysis net ATP gain is 8 and the pyruvate enters the citric acid cycle, oxidized to CO2 and H2O.
Under anaerobic conditions, net ATP gain is 2 from substrate level phosphorylation. NADH gets accumulated which is reoxidized via lactic acid and alcohol fermentation.
Sources of glucose for glycolysis
Glycogen, dietary disaccharides and monosaccharides also enter the glycolytic pathway, since they are the sources of glucose.