Dissimilation is ... The stages of dissimilation

Dissimilation is a complex of chemical reactions in which a gradual decomposition of complex organic substances occurs to simpler ones. This process is accompanied by the release of energy, a significant part of which is used in the synthesis of ATP.

Dissimilation in biology

Dissimilation is a process opposite to assimilation. Nucleic acids, proteins, fats and carbohydrates act as the starting substances to be disintegrated. And the final products are water, carbon dioxide and ammonia. In the organism of animals, the products of decay as they gradually accumulate are discharged outward. And in plants carbon dioxide is released in part, and ammonia is fully used in the assimilation process, serving as a starting material for the biosynthesis of organic compounds.

The relationship between dissimilation and assimilation allows the tissues of the body to be constantly updated. For example, within 10 days, half of the albumin cells are renewed in human blood, and all red blood cells are regenerated within 4 months. The ratio of the intensity of the two opposite metabolic processes depends on many factors. This is the stage of development of the body, and age, and physiological condition. In the course of growth and development in the body, assimilation predominates, as a result new cells, tissues and organs are formed, their differentiation occurs, that is, the body weight increases. In the case of pathologies and fasting, the process of dissimulation 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, depending on the conditions in which dissimilation takes place. These are aerobes and anaerobes. The first for life is free oxygen, the latter do not feel the need for it. In anaerobes, dissimilation proceeds by fermentation, which is the oxygen-free enzymatic cleavage of organic substances to simpler ones. For example, lactic acid or alcohol fermentation.

Stages of dissimilation in aerobic organisms: a preparatory stage

The splitting of organic substances in aerobes is carried out in three steps. At the same time, several definite enzymatic reactions take place on each of them.

The first stage is preparatory. The main role at this stage belongs to multicellular organisms digestive enzymes, located in the gastrointestinal tract. In unicellular animals, enzymes of lysosomes. During the first stage, proteins break down into amino acids, fats form glycerol 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 cleavage and oxidation of glucose, as a result of which free energy is accumulated in the form of 2 ATP molecules. This occurs during 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 acid that a portion of the energy that is released as a result of glycolysis is stored, the remainder is to be dissipated in the form of heat. Chemical reaction of glycolysis: C6H12O6 + 2ADP + 2F → 2C3H4O3 + 2ATP.

Under conditions of a lack of oxygen in plant cells and in yeast cells, pyruvate is split into two substances: ethyl alcohol and carbon dioxide. This is alcohol fermentation.

The amount of energy released during glycolysis is not enough for those organisms that breathe oxygen. This is why lactic acid, which serves as a reserve source of energy and accumulates in the form of lactate, is synthesized in the body of animals and humans under heavy physical loads in muscles. A characteristic feature of this process is the appearance of pain in the muscles.

Oxygen step

Dissimilation is a very complex process, and the third oxygen stage also represents two consecutive reactions. This is the Krebs cycle and oxidative phosphorylation.

During oxygen breath, oxidation of pyruvate occurs to the final products, which are CO2 and H2O. In this case, the energy stored in the form of 36 ATP molecules is released. Then this same energy provides the synthesis of organic substances in the plastic volume. Evolutionary occurrence of this stage is associated with the accumulation of molecular oxygen in the atmosphere and the appearance of aerobic organisms.

The location of oxidative phosphorylation (cellular respiration) is internal mitochondrial membranes, within which there are carrier molecules that transport electrons to molecular oxygen. The energy generated at this stage is partially dispersed in the form of heat, the rest goes to the formation of ATP.

Dissimilation in biology is an energy exchange, the reaction of which looks like this: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38ATF.

Thus, dissimilation is a set of reactions that take place due to organic substances that were previously synthesized by the cell, and free oxygen, which came from the external medium during the process of breathing.