In biological systems, balance is maintained due to the existence of food chains. Each organism takes its place in them, receiving organic molecules for its growth and reproduction. In this case, the process of splitting complex substances into elementary ones that can be absorbed by any cell is called dissimilation. In biology, this is the basis for the existence of living organisms along with assimilation. Dissimilation is also called catabolism, a type of breakdown metabolism.
Stages of Dissimilation
Dissimilation is a complex process involving the digestive systems of the body, which boils down to the production of food components, their processing and metabolism in the cell. A substrate for dissimilation in biology is any complex organic molecule for the cleavage of which the body has the corresponding enzyme systems.
The first stage of catabolism is preparatory. It includes the process of movement to food and its capture. Proteins, fats and carbohydrates in the composition of living or decaying tissues act as food raw materials. The preparatory stage of dissimilation in biology is an example of the nutritional behavior of the body and extracellular digestion. During it, unicellular organisms receive complex organic raw materials, phagocytize it and break down it into elementary components.
In multicellular organisms, the preparatory stage of dissimilation means the process of movement to food, its preparation and digestion in the digestive system, after which elementary nutrients are carried by the circulatory system to the cells. Plants also have a preparatory phase. It consists in the absorption of organics rotting products, which are later delivered via transport systems to the site of intracellular dissimilation. In biology, this means that for the growth and reproduction of plants, a substrate is required, the destruction of which is carried out by low-organized organisms, such as rotting bacteria.
Anaerobic Dissimilation
The second stage of dissimilation is called oxygen-free, that is, anaerobic. It mainly concerns carbohydrates and fats, because amino acids are not metabolized, but are sent to the site of biosynthesis. Protein macromolecules are built from them, and therefore the use of amino acids is an example of assimilation, that is, synthesis. Dissimilation is (in biology) the breakdown of organic molecules with the release of energy. Moreover, almost all organisms are able to metabolize glucose - a universal monosaccharide, which is the main source of energy for all living things.
During anaerobic glycolysis, 2 ATP molecules are synthesized, which store energy in macroergic bonds. This process is ineffective, and therefore requires a large consumption of glucose with the formation of many metabolites: pyruvate, or lactic acid, in some organisms - ethyl alcohol. These substances will be used in the third stage of dissimilation, but ethanol will be disposed of by the body without energy benefits to prevent intoxication. At the same time, fatty acids as products of the breakdown of fats cannot be metabolized by obligate anaerobes, since they require aerobic cleavage pathways involving acetyl-coenzyme-A.
Aerobic dissimilation
Oxygen dissimilation in biology is aerobic glycolysis, a process of splitting glucose with a high energy yield. It comprises 36 ATP molecules, which is 18 times more effective than oxygen-free glycolysis. In the human body, there are two stages of glycolysis, and therefore the total energy output during the metabolism of one glucose molecule is already 38 ATP molecules. 2 molecules are formed at the stage of oxygen-free glycolysis, and another 36 during aerobic oxidation in mitochondria. Moreover, in some cells under conditions of oxygen deficiency, which is observed with coronary disease, the consumption of metabolites can go only along the oxygen-free path.
Metabolism of aerobes and anaerobes
Dissimilation in anaerobic and aerobic organisms is similar. However, under no circumstances can anaerobes participate in aerobic oxidation. This means that they cannot have a third stage of dissimilation. Organisms that have enzymatic systems for oxygen binding, for example, cytochrome oxidase, are capable of aerobic oxidation, and therefore, they metabolize energy more efficiently during metabolism. Therefore, oxygen dissimilation in biology is an example of the most effective metabolic pathway for the breakdown of glucose, which allowed warm-blooded organisms with a developed nervous system to appear. At the same time, nerve cells do not have enzymes responsible for the breakdown of other metabolites, therefore they can only break down glucose.