In biological systems, the 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. At the same time, the process of splitting complex substances into elementary ones that can be assimilated 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 splitting metabolism.
Stages of dissimilation
Dissimilation is a complex process involving the digestive systems of the body, which comes down to obtaining food components, their processing and metabolism in the cell. A substrate for dissimilation in biology is any complex organic molecule for which the body has the appropriate enzyme systems to break down.
The first stage of catabolism is preparatory. It includes the process of movementto 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 an organism's feeding behavior and extracellular digestion. During it, unicellular organisms receive complex organic raw materials, phagocytize it and break it down to elementary components.
In multicellular organisms, the preparatory stage of dissimilation means the process of movement to food, its receipt and digestion in the digestive system, after which elemental nutrients are carried by the circulatory system to the cells. Plants also have a preparatory stage. It consists in the absorption of decay products of organic matter, which are later delivered by transport systems to the place 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-organisms, such as decay bacteria.
Anaerobic dissimilation
The second stage of dissimilation is called oxygen-free, that is, anaerobic. It is more about 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. At the same time, almost all organisms are able to metabolize glucose, a universal monosaccharide thatis 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 inefficient, 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 utilized by the body without energy benefits to prevent intoxication. At the same time, fatty acids, as products of fat breakdown, 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 glucose breakdown with a high energy yield. It is 36 ATP molecules, which is 18 times more efficient than anoxic 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. At the same time, in some cells under conditions of oxygen deficiency, which is observed in ischemic disease, the consumption of metabolites can only go along the oxygen-free path.
Metabolism of aerobes and anaerobes
Dissimilation in anaerobic andaerobic 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 enzyme systems for oxygen binding, for example, cytochrome oxidase, are capable of aerobic oxidation, and therefore, in the course of metabolism, they receive energy more efficiently. Therefore, oxygen dissimilation in biology is an example of the most efficient metabolic pathway for the breakdown of glucose, which allowed the emergence of warm-blooded organisms with a developed nervous system. At the same time, nerve cells do not have enzymes responsible for the breakdown of other metabolites, therefore they are only able to break down glucose.
