Dissimilation is a complex of chemical reactions in which a gradual decomposition of complex organic substances to simpler ones occurs. 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 the opposite of assimilation. Nucleic acids, proteins, fats and carbohydrates are used as starting substances to be decomposed. And the final products are water, carbon dioxide and ammonia. In the body of animals, decay products, as they gradually accumulate, are brought out. And in plants, carbon dioxide is partially released, and ammonia is fully used in the process of assimilation, serving as the starting material for the biosynthesis of organic compounds.
The relationship of dissimilation and assimilation allows the body's tissues to be constantly updated. For example, within 10 days, half of albumin cells are renewed in human blood, and all red blood cells are regenerated in 4 months. The ratio of the intensity of two opposite metabolic processes depends on many factors. This is the stage of development of the body, and age, and physiological state. During growth and development, assimilation predominates 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 starvation, 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, depending on the conditions under which dissimilation proceeds. These are aerobes and anaerobes. The former require free oxygen for life, 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 to simpler ones. For example, lactic acid or alcoholic fermentation.
Stages of dissimilation in aerobic organisms: preparatory stage
The breakdown of organic matter in aerobes is carried out in three steps. Moreover, on each of them there are several specific enzymatic reactions.
The first stage is preparatory. In multicellular organisms, the main role at this stage belongs to the digestive enzymes located in the gastrointestinal tract. In unicellular organisms, to lysosome enzymes. 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 breakdown and oxidation of glucose, as a result of which free energy accumulates in the form of 2 ATP molecules. This occurs during several successive reactions, the final result of which is the formation of two pyruvate molecules and the same amount of ATP from one glucose molecule. It is in the form of adenosine triphosphoric acid that part of the energy that is released as a result of glycolysis is stored, the rest is subject to dissipation in the form of heat. Chemical reaction of glycolysis: 612O6 + 2 + 2 → 234O3 + 2.
In conditions of a lack of oxygen in plant cells and in yeast cells, pyruvirite is split into two substances: ethyl alcohol and carbon dioxide. This is alcoholic fermentation.
The amount of energy released during glycolysis is not enough for those organisms that breathe oxygen. That is why in animals and humans, with great physical exertion in the muscles, lactic acid is synthesized , which serves as a backup source of energy and accumulates in the form of lactate. A characteristic feature of this process is the appearance of muscle pain.
Oxygen phase
Dissimilation is a very complex process, and the third oxygen phase also represents two successive reactions. It is a Krebs cycle and oxidative phosphorylation.
During oxygen respiration, pyruvrate is oxidized to the final products, which are CO2 and H2O. This releases energy stored in the form of 36 ATP molecules. Then the same energy provides the synthesis of organic substances in a plastic volume. The evolutionary occurrence of this stage is associated with the accumulation of molecular oxygen in the atmosphere and the appearance of aerobic organisms.
The site of oxidative phosphorylation (cellular respiration) is the inner mitochondrial membrane, inside which there are carrier molecules that transport electrons to molecular oxygen. The energy generated at this stage is partially dissipated in the form of heat, while 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 combination of reactions that occur due to organic substances that were previously synthesized by the cell, and free oxygen, which came from the external environment during breathing.