Glycolysis involves biocatalytically controlled breakdown of simple sugars such as D-glucose in humans and in almost all multicellular organisms. The degradation and conversion process of glucose to pyruvate occurs in ten sequential steps and can occur under aerobic and anaerobic conditions alike. Glycolysis is used for energy production, and pyruvate provides an initial precursor for the biochemical synthesis of certain substances. The breakdown of higher-order carbohydrates (polysaccharides) also undergoes glycolysis after being broken down into simple sugars.
What is glycolysis?
Glycolysis is a central metabolic process for the breakdown of the simple sugar D-glucose and occurs within cells in the cytosol, the liquid portion of the cell plasma. Glycolysis is a central metabolic process for the breakdown of the simple sugar D-glucose and takes place within the cells in the cytosol, the liquid portion of the cell plasma. The degradation process occurs in 10 consecutive enzymatically controlled individual steps. The end products of the total balance from glycolysis per glucose molecule are 2 pyruvate molecules, 2 ATP nucleotides and 2 NADH nucleotides. The 10 individual steps can be divided into two phases, the preparation phase from step 1 to step 5 and the amortization phase from step 6 to 10. The preparation phase is energetically negative for the metabolism, so that energy must be supplied in the form of 2 ATP. Only the amortization phase is energetically positive, resulting in a net energy gain in the form of 2 ATP nucleotides and 2 NADH nucleotides. In each of the first two steps of glycolysis, 2 phosphate groups are transferred to the glucose, derived from 2 ATP nucleotides (adenosine triphosphate), which are thereby converted to ADP nucleotides (adenosine diphosphate). While glycolysis up to the formation of pyruvate is independent of whether oxic (aerobic) or anoxic (anaerobic) conditions prevail, further metabolism of pyruvate is dependent on whether oxygen is available or not. However, strictly speaking, the further degradation and conversion processes are no longer part of glycolysis.
Function and task
Glycolysis is one of the most important and common central metabolic processes that occur within a cell. The task and function of glycolysis is the energetic and material metabolization of the simple sugar D-glucose. The energy carrier and energy supplier in this process is ATP, which is obtained in the course of energy metabolism by supplying energy and transferring a phosphate group to an ADP nucleotide. The route via the ATP has the advantage that the energy is stored for a short time and is not lost via heat dissipation. In addition, the ATP can be transported over short distances to the place where the energy is needed at the moment. Energy-positive glycolysis additionally provides the cell with pyruvate. It can either be introduced into the citrate cycle and the subsequent respiratory chain under “consumption” of oxygen under oxic conditions in the mitochondria of the cells for further energy production, or it can be used as a starting material for the synthesis of required substances. In the citrate cycle, CO2 (carbon dioxide) and H2O (water) are produced as the main degradation products. The energy released during the oxidation process is used in the respiratory chain to phosphorylate ADP to ATP and thus stored for a short time. The complete degradation of glucose to water and carbon dioxide with the addition of oxygen is more energetically productive, but has the disadvantage that it can only take place under oxic conditions, i.e., conditions under which molecular oxygen is available in sufficient quantities. When skeletal muscles are required to perform at high levels, oxygen delivery to muscle cells is too slow, so they must draw the necessary energy from glycolysis. Another advantage of glycolysis lies in its high process speed, which reaches a multiple of the conversion rate within the citrate cycle.
Diseases and ailments
Glycolysis embodies one of the oldest and most stable metabolic processes of living organisms in evolutionary history. It is likely that glycolysis was evolved as one of the basic metabolic processes as early as 3.5 billion years ago, well before the development of multicellular organisms, because all living organisms are capable of glycolysis and use it for energy production.There are only a few known disorders or diseases that are explicitly causally associated with a disturbance of glycolysis. Disturbances in the course of glycolysis primarily lead to serious effects in the red blood cells (erythrocytes). Because they do not contain mitochondria, they depend on energy supply by glycolysis. If the energy supply is disturbed, hemolysis occurs, i.e. the membranes of the erythrocytes dissolve and the hemoglobin passes directly into the serum. Usually, there is a deficiency of the enzyme pyruvate kinase, so that the glycolysis process is interrupted. Another cause leading to similar symptoms may be due to the erythrocytes themselves, if they do not have enough of the necessary enzyme KKR (isoenzyme of pyruvate kinase). Tarui disease (Tarui’s disease) is one of the few diseases that cause a direct disturbance in the process of glycolysis. It is a glycogen storage disease. Excess glucose in the blood serum is temporarily converted by the body into polymeric sugars (glycogen), which is later converted back into glucose when needed to be metabolized (metabolized) via glycolysis. In the case of Tarui disease, due to an inherited genetic defect, there is a deficiency of phosphofructokinase, an enzyme that causes the phophorylation and conversion of glucose to fructose-1,6-biphosphate (3rd step within glycolysis). Enzyme deficiency causes interruption of glycolysis so that skeletal muscles are not properly supplied with energy. Painful muscle spasms and hemolytic anemia, dissolution of the membrane of red blood cells, occur.
