A cell is an elementary unit of all organisms. The degree of activity, the ability to adapt to environmental conditions depends on its condition. The vital processes of the cell are subject to certain laws. 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 cell formation and cell death or division. During the interphase period, practically all the basic processes of cell activity are actively proceeding : nutrition , respiration, growth, irritability, movement. Cell reproduction is carried out only in phase M.
Interphase periods
Cell growth time between divisions is divided into several stages:
- presynthetic, or phase G-1, is the initial period: the synthesis of messenger RNA, proteins and some other cellular elements;
- synthetic, or phase S: DNA duplication;
- postsynthetic, or G-2 phase: preparation for mitosis.
In addition, some cells after differentiation cease to divide. There is no G-1 period in their interphase. They are in the so-called resting phase (G-0).
Metabolism
As already mentioned, the vital processes of a living cell for the most part occur during interphase. The main of them is metabolism. Thanks to him, not only various internal reactions occur, but also intercellular processes that connect individual structures to the whole organism.
A certain pattern is inherent in metabolism. The vital processes of a cell are largely dependent on its observance, the absence of any violations in it. Substances, before affecting the intracellular environment, must penetrate through the membrane. Then they undergo certain processing in the process of nutrition or respiration. At the next stage, the resulting processed products are used to synthesize new elements or transform existing structures. The metabolic products remaining after all the transformations, which are harmful to the cell or simply are not needed by it, are removed to the external environment.
Assimilation and dissimilation
Enzymes are involved in the regulation of the successive change in the conversion of one substance to another. They contribute to the faster flow of certain processes, that is, they act as catalysts. Each such “accelerator” affects only a specific transformation, directing the flow of the process in one direction. Newly formed substances are further exposed to other enzymes that contribute to their further transformation.
Moreover, all the vital processes of a cell are somehow connected with two opposite trends: assimilation and dissimilation. For metabolism, their interaction, balance or some confrontation is the basis. A variety of substances received from the outside are converted under the action of enzymes in the usual and necessary for the cell. These synthetic transformations are called assimilation. Moreover, energy is needed for such reactions. Its source is the processes of dissimilation, or destruction. The breakdown of the substance is accompanied by the release of energy necessary for the basic processes of cell activity to occur. Dissimilation also contributes to the formation of simpler substances, which are then used for the new synthesis. Part of the decay products is thus excreted.
The processes of cell activity are often associated with a balance of synthesis and decay. Thus, growth is possible only with the predominance of assimilation over dissimilation. It is interesting that a cell cannot grow indefinitely: certain boundaries are laid in it, upon reaching which growth stops.
Penetration
Transportation of substances from the environment into the cell is carried out passively and actively. In the first case, transfer becomes possible due to diffusion and osmosis. Active transportation is accompanied by the expenditure of energy and often occurs contrary to 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.
Characteristics of substances affect the degree of permeability of the cell membrane for them . So, organic substances enter the cytoplasm more easily than inorganic ones. For permeability, the size of the molecules also matters. Also, the properties of the membrane depend on the physiological state of the cell and environmental features such as temperature and illumination.
Food
In the entry of substances from the environment, fairly well-studied vital processes take part: the respiration of the cell and its nutrition. The latter is carried out using 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 forms, and then bubbles from the membrane containing food particles arise. Gradually they are released from the shell. Then the particles are exposed to processes very close to digestion. After a series of transformations, substances are split into simpler ones and are used to synthesize the elements necessary for the cell. At the same time, part of the resulting substances is released into the environment, since it is not subject to further processing or use.
Breath
Nutrition is not the only process that contributes to the appearance of necessary elements in the cell. Breathing is in essence very similar to it. It represents a series of successive transformations of carbohydrates, lipids and amino acids, as a result of which new substances arise: carbon dioxide and water. The most important part of the process is the formation of energy, which is stored in the cell in the form of ATP and some other compounds.
Involving oxygen
The vital processes of a human cell, like many other organisms, are inconceivable without aerobic respiration. The main substance necessary for it is oxygen. The release of much-needed energy, as well as the formation of new substances occurs as a result of oxidation.
The breathing process is divided into two stages:
Glycolysis is the breakdown of glucose in the cytoplasm of a cell by the action of enzymes without the participation of oxygen. It represents eleven reactions successively replacing each other. As a result, two ATP molecules are formed from one glucose molecule. The decay products then fall into the mitochondria, where the oxygen phase begins. As a result of several reactions, carbon dioxide, additional ATP molecules and hydrogen atoms are formed. In general, a cell receives 38 ATP molecules from one glucose molecule. It is because of the large amount of stored energy that aerobic respiration is considered more effective.
Anaerobic respiration
Bacteria have a different type of respiration. Instead of oxygen, they use sulfates, nitrates, and more. This type of breathing is less effective, but it plays a huge role in the circulation of substances in nature. Thanks to anaerobic organisms, the biogeochemical cycle of sulfur, nitrogen and sodium is carried out. In general, the processes proceed similarly to oxygen respiration. After glycolysis is complete, the resulting substances enter into a fermentation reaction, which can result in ethyl alcohol or lactic acid.
Irritability
The cell constantly interacts with the environment. The response 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 features. Muscle cells respond with contraction, gland cells with secretion, and neurons with nerve impulse generation. It is 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 vital processes of the cell in it are repeated during the entire period of the interphase and terminate either in the death of the cell or in its division. Self-reproduction is the key to preserving life in general after the disappearance of a particular organism. During cell growth, assimilation exceeds dissimilation; volume grows faster than the surface. As a result, the vital processes of the cell are inhibited, deep transformations begin, after which the existence of the cell becomes impossible, it proceeds to division. At the end of the process, new cells are formed with increased potential and metabolism.
This is not to say which vital processes of the cell play the most important role. All of them are interconnected and meaningless in isolation from each other. The subtle and streamlined mechanism of the work existing in the cell once again reminds of the wisdom and grandeur of nature.