Dissimilation, or energy metabolism. In this process, the macromolecular organic substances are transformed into simple organic and inorganic. This process is multistage and complex. Schematically it can be reduced to the following three phases:
the First stage — preparatory. High molecular weight organic substances are enzymatically converted into more simple: proteins into amino acids, starch to glucose, fats to glycerol and fatty acids. Energy this releases a little and it turns into a form of thermal energy.
Second stage — oxygen-free. Formed in the first stage of substances under the action of enzymes undergo further decay. As example is the glycolysis — fermentative oxygen-free disintegration of a molecule of glucose to two molecules of lactic acid in the cells of animal organisms. This process is multi-stage (it has been implemented by 13 enzymes), and only in the most General form can be depicted as:
C6H12O6 → 2C3H6O3 + free energy.
as the reaction of glycolysis at each stage is allocated a free energy. The total quantity is distributed as follows: one part (≈60%) is dissipated as heat, and the other (“≈0%) is retained in the cell and then used. The preservation of the deposited energy occurs through the space above the system “ATP⇔ADP”. In this case, due to the energy released during anoxic breakdown of one molecule of glucose, two molecules of ADP are converted to two molecules of ATP. Later energy as would be conserved in ATP molecules will be used (during the reverse transformation to ADP) in the process of assimilation, the excitation transfer and so on
Another example of the anaerobic phase of energy metabolism may serve alcoholic fermentation in which one glucose molecule ultimately formed two molecules of ethanol, two molecules of CO2 and a certain amount of free energy.
C6H12O6 → 2CO2 + 2C2H5OH + the free energy.
the Third stage is oxygen. This is the final stage of breakdown of organic substances by oxidation with oxygen in the air to simple inorganic CO2 and H2O. This releases the maximum amount of available energy, much of which is also reserved in the cell through the formation of ATP molecules. Thus, two molecules of lactic acid, oxidized to CO2 and H2O transmit part of its energy 36 ATP molecules. It is easy to see that the third stage of energy exchange to the greatest extent provides a cage free energy, which is stored through the synthesis of ATP.
All the process of ATP synthesis are carried out in the mitochondria of cells and is universal for all living things. Thus, the processes of dissimilation in the cell occur due to the organic substances, previously synthesized by the cell, and the free oxygen from the external environment through the breath. In this case, the cell accumulates energy-rich ATP molecules, and the external environment are displayed the carbon dioxide and excess amount of water. In anaerobic organisms that live in oxygen-free environment, the last stage of dissimilation is slightly different chemically, but also with the accumulation of ATP molecules.
This post is also available in Білоруська, Český, Deutsche, Español, Suomalainen, Français, Italiano, 日本, Norsk, Polski, Portugues, Русский, Українська and 中國.