Glycolysis is the breakdown of glucose into a compound called pyruvate. A net of two ATPs are produced as the process uses two ATPs and produces four. Glycolysis consists of ten chemical reactions; each reaction is catalysed using a different enzyme. Oxygen is not required during glycolysis so it is considered anaerobic respiration. Glycolysis must be regulated so that energy is produce only when required. During glycolysis there are three enzymes that catalyse or inhibit the rate of reaction.
These are hexokinase, phosphofructokinase and pyruvate kinase. During the first reaction of glycolysis, glucose 6 phosphate is produced. High concentrations of this molecule signal that a cell no longer requires glucose for energy. Phosphofructokinase (PKF) is a key enzyme in the regulation of glycolysis. PKF is the enzyme that catalyses the reaction producing fructose 1, 6 phosphate. High concentrations of ATP inhibit PKF, thus regulating glycolysis. PFK is also inhibited by high concentrations of citrate, another marker of a high energy state of a cell.
When citrate levels are high, the cell can get enough energy from the citric acid cycle and does not need glycolysis to shovel more carbons into the citric acid cycle. Enzymes require very specific environmental conditions to function at at their optimum level e. g. pH and temperature. The breakdown of glucose (glycolysis) produces hydrogen ions. The presence of hydrogen ions creates an acidic environment. This acidic environment slows down enzyme activity and ultimately the breakdown of glucose, this slows down respiration.
Anaerobic glycolysis is the process by which the normal pathway of glycolysis is routed to produce lactate. It happens when energy is required in the absence of oxygen. It is vital for tissues with high energy requirements, like muscle cells. If there is not enough oxygen then NADH cannot release hydrogen ions and they build up in the cell. The normal pH of muscle cells is around 7 (neutral) if the build-up of hydrogen ions continues, the pH will reduce and muscle function will be impaired. This is what causes the burning sensation.