Dissimilation is a complex of chemical reactions, inwhich occurs the gradual decomposition of complex organic substances to more simple. This process is accompanied by the release of energy, much of which is used in the synthesis of ATP.
Dissimilation in biology
Dissimilation is the opposite process.assimilation. Nucleic acids, proteins, fats and carbohydrates are the starting substances to be decomposed. And the final products are water, carbon dioxide and ammonia. In animals, the decay products with the gradual accumulation are displayed outside. And in plants, carbon dioxide is partially emitted, and ammonia is fully used in the assimilation process, serving as the starting material for the biosynthesis of organic compounds.
The relationship of dissimilation and assimilation allowsbody tissues are constantly being updated. For example, within 10 days, half of the albumin cells are renewed in human blood, and in 4 months all red blood cells are regenerated. The intensity ratio of the two opposite metabolic processes depends on many factors. This is the stage of development of the body, and age, and physiological state. In the course of growth and development, assimilation prevails in the body, as a result, new cells, tissues and organs are formed, their differentiation occurs, that is, body weight increases. In the case of pathologies and during fasting, the process of dissimilation prevails over assimilation, and the body decreases in weight.
Classification of organisms by the nature of dissimilation
All organisms can be divided into two groups, independing on the conditions in which dissimilation occurs. These are aerobes and anaerobes. The first for life requires free oxygen, the latter do not feel the need for it. In anaerobes, dissimilation proceeds by fermentation, which is an oxygen-free enzymatic breakdown of organic substances into simpler ones. For example, lactic acid or alcoholic fermentation.
Stages of dissimilation in aerobic organisms: the preparatory stage
The splitting of organic matter in aerobes is carried out in three steps. At the same time on each of them there are several specific enzymatic reactions.
The first stage is preparatory.The main role at this stage belongs to the multicellular organisms digestive enzymes in the gastrointestinal tract. In unicellular lysosome enzymes. During the first stage, proteins break down into amino acids, fats form glycerin and fatty acids, polysaccharides are split into monosaccharides, nucleic acids into nucleotides.
Glycolysis
The second stage of dissimilation is glycolysis.It flows without oxygen. The biological essence of glycolysis is that it represents the beginning of the breakdown and oxidation of glucose, resulting in the accumulation of free energy in the form of 2 ATP molecules. This occurs in the course of several successive reactions, the final result of which is the formation of two molecules of pyruvate from the same glucose molecule and the same amount of ATP. It is in the form of adenosine triphosphate that part of the energy that is released as a result of glycolysis is stored. The rest is subject to dissipation as heat. Chemical reaction of glycolysis: C6H12O6 + 2ADF + 2F → 2C3H4O3 + 2ATP.
Under conditions of lack of oxygen in plant cells and in yeast cells, pyruvirate is split into two substances: ethyl alcohol and carbon dioxide. This is alcohol fermentation.
The amount of energy released during glycolysis,not enough for those organisms that breathe oxygen. That is why lactic acid is synthesized in the body of animals and humans during heavy physical exertion in muscles, which serves as a reserve source of energy and accumulates in the form of lactate. A characteristic feature of this process is the appearance of pain in the muscles.
Oxygen stage
Dissimilation is a very complex process, and the third oxygen stage also consists of two successive reactions. This is the Krebs cycle and oxidative phosphorylation.
During oxygen respiration, oxidation occurs.pyruvirate to the final products, which are CO2 and H2O. At the same time, the energy stored in the form of 36 ATP molecules is released. Then the same energy provides the synthesis of organic substances in the plastic volume. The evolutionary emergence of this stage is associated with the accumulation of molecular oxygen in the atmosphere and the appearance of aerobic organisms.
The site of the oxidativephosphorylation (cellular respiration) are the inner membranes of mitochondria, inside of which there are carrier molecules that transport electrons to molecular oxygen. The energy formed at this stage is partially dissipated in the form of heat, the rest goes to the formation of ATP.
Dissimilation in biology is energy metabolism, the reaction of which looks like this: С6Н12O6 + 6О2 → 6СО2 + 6Н2O + 38АТФ.
Thus, dissimilation is a collectionreactions occurring due to organic substances, which were previously synthesized by the cell, and free oxygen, which came from the external environment during respiration.
