The main processes of cell life

A cell is an elementary unit of all organisms. From its state depends degree of activity, the ability to adapt to environmental conditions. The processes of cell life are subject to certain regularities. The degree of activity of each of them depends on the phase of the life cycle. In total, they are distinguished by two: interphase and division (phase M). The first takes time between the formation of the cell and its death or division. During the interphase period, almost all the basic processes of the cell's vital activity are active : nutrition , respiration, growth, irritability, and movement. Reproduction of the cell occurs only in the phase of M.

Interphase Periods

The time of cell growth between the divisions is divided into several stages:

• Presynthetic, or phase G-1, - the initial period: synthesis of matrix RNA, proteins and some other cellular elements;
• Synthetic, or phase S: DNA doubling;
• Post-synthetic, or G-2 phase: preparation for mitosis.

In addition, some cells after differentiation cease to divide. In their interphase there is no G-1 period. They are in the so-called rest phase (G-0).

Metabolism

As already mentioned, the processes of vital activity of a living cell for the most part occur during the interphase period. The main one is metabolism. Thanks to him not only various internal reactions take place, but also intercellular processes that connect individual structures to the whole organism.

Exchange of substances is inherent in a certain scheme. The processes of vital activity of a cell largely depend on its observance, absence of any violations in it. Substances, before affecting the intracellular environment, must penetrate the membrane. Then they undergo certain processing in the process of feeding or breathing. At the next stage, the processed products are used to synthesize new elements or transform existing structures. Remaining after all transformations, exchange products that are harmful to the cell or simply do not need it, are removed to the external environment.

Assimilation and dissimilation

The regulation of a consistent change in the transformation of certain substances into others is performed by enzymes. They contribute to a faster flow of certain processes, that is, act as catalysts. Each such "accelerator" affects only a specific transformation, directing the flow of the process in one direction. The newly formed substances are further subjected to the action of other enzymes that promote their further transformation.

At the same time, all the processes of cell life are connected in one way or another with two opposite tendencies: assimilation and dissimilation. For metabolism, their interaction, balance or some opposition are the basis. Various substances that come from outside are transformed under the action of enzymes into habitual and necessary for cells. These synthetic transformations are called assimilation. In this case, for such reactions, energy is needed. Its source is the processes of dissimilation, or destruction. The disintegration of the substance is accompanied by the release of energy necessary for the main processes of the vital activity of the cell to proceed. Dissimilation also promotes the formation of simpler substances, which are then used for a new synthesis. Part of the decay products is output in this case.

The processes of cell activity are often associated with the balance of synthesis and decay. So, growth is possible only with the predominance of assimilation over dissimilation. It is interesting that the cell can not grow infinitely: it contains certain boundaries, upon which growth stops.

Penetration

Transportation of substances from the environment into the cell is passively and actively. In the first case, transfer becomes possible due to diffusion and osmosis. Active transportation is accompanied by energy expenditure and often occurs in spite of these processes. Thus, for example, potassium ions penetrate. They are injected into the cell, even if their concentration in the cytoplasm exceeds its level in the external environment.

The characteristics of the substances affect the degree of permeability to them of the cell membrane. Thus, organic substances enter the cytoplasm more easily than inorganic substances . For the permeability, the size of the molecules also matters. Also, the properties of the membrane depend on the physiological state of the cell and such characteristics of the environment as temperature and illumination.

Food

In the intake of substances from the environment, fairly well-studied processes of vital activity take part: the respiration of the cell and its nutrition. The latter is carried out with the help of pinocytosis and phagocytosis. The mechanism of both processes is similar, but during pinocytosis, smaller and denser particles are captured. Molecules of the absorbed substance are adsorbed by the membrane, captured by special outgrowths and immersed with them inside the cell. As a result, a channel is formed, followed by bubbles from the membrane containing food particles. Gradually they are released from the shell. Further, the particles are exposed to very close to digestion processes. After a number of transformations, the substances split into simpler ones and are used to synthesize the elements necessary for the cell. At the same time, some of the produced substances are released into the environment, as it is not subject to further processing or use.

Breath

Nutrition is not the only process that promotes the appearance in the cell of the necessary elements. Breathing is very similar to it. It represents a series of successive transformations of carbohydrates, lipids and amino acids, as a result of which new substances appear: carbon dioxide and water. The most important part of the process is the formation of energy, which is stored by the cell in the form of ATP and some other compounds.

With the participation of oxygen

The processes of the life of a human cell, like many other organisms, are inconceivable without aerobic respiration. The main substance necessary for him is oxygen. The release of much-needed energy, as well as the formation of new substances occurs as a result of oxidation.

The process of breathing is divided into two stages:

• Glycolysis;

• Oxygen stage.

Glycolysis is the cleavage of glucose in the cytoplasm of a cell under the action of enzymes without the participation of oxygen. It represents eleven consecutively replacing each other's reactions. As a result, two molecules of ATP are formed from one glucose molecule. The products of decomposition fall into the mitochondria, where the oxygen stage begins. As a result of several other reactions, carbon dioxide, additional ATP molecules and hydrogen atoms are formed. In general, the cell receives 38 molecules of ATP from one glucose molecule. It is because of the large amount of stored energy that aerobic respiration is considered to be more effective.

Anaerobic respiration

There is another type of respiration for bacteria. Instead of oxygen, they use sulfates, nitrates and the like. This type of breathing is less effective, however it plays a huge role in the circulation of substances in nature. Thanks to anaerobic organisms, a biogeochemical cycle of sulfur, nitrogen and sodium is carried out. In general, the processes proceed similarly to oxygen breathing. After the termination of glycolysis, the formed substances enter into a fermentation reaction, the result of which can be ethyl alcohol or lactic acid.

Irritability

The cell constantly interacts with the environment. The answer to the influence of various external factors is called irritability. It is expressed in the transition of the cell to an excitable state and the occurrence of a reaction. The type of response to external influences differs depending on the functional characteristics. Muscle cells respond with contraction, gland cells - secretion secretion, and neurons - generation of a nerve impulse. It is the irritability that underlies many physiological processes. Thanks to it, for example, nervous regulation is carried out: neurons are able to transmit excitation not only to similar cells, but also to elements of other tissues.

Division

Thus, there is a certain cyclic scheme. The processes of the cell's life in it are repeated during the entire period of the interphase and are completed either by cell death or by its division. Self-reproduction is the key to saving life as a whole after the disappearance of a particular organism. During cell growth, assimilation exceeds dissimilation, the volume grows faster than the surface. As a result, the processes of vital activity of the cell are inhibited, deep transformations begin, after which the existence of the cell becomes impossible, it passes to division. At the end of the process, new cells are formed with increased potential and metabolism.

It is impossible to say which vital processes of the cell play the most important role. All of them are interrelated and meaningless in isolation from each other. Thin and well-functioning mechanism of work that exists in the cage, once again recalls the wisdom and grandeur of nature.