Cell is the elementary unit of all organisms. The degree of activity, the ability to adapt to environmental conditions depends on its state. The life processes of the cell are subject to certain patterns. The degree of activity of each of them depends on the phase of the life cycle. In total, there are two of them: interphase and division (phase M). The first takes the time between the formation of a cell and its death or division. During the period of interphase, almost all the main processes of the cell's vital activity are actively proceeding: nutrition, respiration, growth, irritability, movement. Cell reproduction is carried out only at the M phase.
Interphase periods
The time of cell growth between divisions is divided into several stages:
- presynthetic, or phase G-1, - initial period: synthesis of messenger RNA, proteins and some other cellular elements;
- synthetic, or phase S: DNA doubling;
- postsynthetic, or G-2 phase: preparation for mitosis.
In addition, some cells stop dividing after differentiation. In theirthere is no G-1 period in the 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 proceed during the interphase period. The main one is metabolism. Thanks to it, not only various internal reactions take place, but also intercellular processes that connect individual structures into the whole organism.
Metabolism has a certain pattern. The vital processes of a cell largely depend on its observance, the absence of any disturbances in it. Substances must penetrate the membrane before affecting the intracellular environment. Then they undergo a certain processing in the process of nutrition or respiration. At the next stage, the resulting processing 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 not needed by it, are removed to the external environment.
Assimilation and dissimilation
Enzymes are involved in the regulation of the successive change of transformations of one substance into 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 process in one direction. The newly formed substances are further exposed to other enzymes that contribute to their further transformation.
At the same time, everythingthe processes of cell vital activity are connected in one way or another with two opposite tendencies: assimilation and dissimilation. For metabolism, their interaction, balance or some opposition is the basis. A variety of substances that come from outside are converted under the action of enzymes into the usual and necessary for the cell. These synthetic transformations are called assimilation. However, these reactions require energy. Its source is the processes of dissimilation, or destruction. The decay of a substance is accompanied by the release of energy necessary for the basic processes of the cell's vital activity to proceed. Dissimilation also promotes the formation of simpler substances, which are then used for new synthesis. Some of the decay products are removed.
The life processes of a cell are often associated with the balance of synthesis and decay. Thus, growth is possible only if assimilation prevails over dissimilation. Interestingly, a cell cannot grow indefinitely: it has certain boundaries, upon reaching which growth stops.
Infiltration
Transportation of substances from the environment into the cell is carried out passively and actively. In the first case, the transfer becomes possible due to diffusion and osmosis. Active transport 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 inenvironment.
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 light.
Food
Quite well-studied vital processes take part in the intake of substances from the environment: cell respiration and its nutrition. The latter is carried out with the help of pinocytosis and phagocytosis.
The mechanism of both processes is similar, but smaller and denser particles are captured during pinocytosis. 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, and then bubbles appear from the membrane containing food particles. Gradually, they are released from the shell. Further, the particles are exposed to processes very close to digestion. After a series of transformations, the substances are broken down into simpler ones and used to synthesize the elements necessary for the cell. At the same time, part of the formed substances is discharged into the environment, since it is not subject to further processing or use.
Breathing
Nutrition is not the only process that contributes to the appearance of the necessary elements in the cell. Breath byits essence is very similar to it. It is 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 by the cell in the form of ATP and some other compounds.
With oxygen
The life 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;
- oxygen stage.
Glycolysis is the breakdown of glucose in the cytoplasm of a cell under the action of enzymes without the participation of oxygen. It consists of eleven successive reactions. As a result, two ATP molecules are formed from one glucose molecule. The decay products then enter the mitochondria, where the oxygen stage begins. As a result of several more reactions, carbon dioxide, additional ATP molecules and hydrogen atoms are formed. In general, the 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 efficient.
Anaerobic respiration
Bacteria have a different type of respiration. They use sulfates, nitrates, and so on instead of oxygen. This type of breathing is less efficient, but it plays a huge role.role in the cycle of matter 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 the end of glycolysis, the resulting substances enter into a fermentation reaction, which may 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 influence differs depending on the functional features. Muscle cells respond by contraction, gland cells by secretion, and neurons by generating a nerve impulse. 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 pattern. The life processes of the cell in it are repeated during the entire period of interphase and end either with the death of the cell or its division. Self-reproduction is the key to the preservation of life in general after the disappearance of a particular organism. During cell growth, assimilation exceeds dissimilation, the volume grows faster than the surface. As a result, processesthe vital activity of the cell is 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.
It is impossible to say which processes of cell vital activity play the most important role. All of them are interconnected and meaningless in isolation from each other. The subtle and well-oiled mechanism of work that exists in the cell once again reminds us of the wisdom and grandeur of nature.
