Cell: food and building. The value of cell nutrition. Examples of cell nutrition

Modern experimental studies have established that the cell is the most complex structural and functional unit of virtually all living organisms, with the exception of viruses that are non-cellular forms of life. Cytology studies the structure, as well as the life of the cell: breathing, nutrition, reproduction, growth. These processes will be considered in this paper.

Cell structure

Using a light and electron microscope, biologists have determined that plant and animal cells contain a surface device (supramembrane and sub-membrane complexes), cytoplasm and organelles. In animal cells, a glycocalyx containing enzymes is located above the membrane and provides nutrition to cells outside the cytoplasm. In plant cells, prokaryotes (bacteria and cyanobacteria), as well as fungi, a cell wall is formed above the membrane, which consists of cellulose, lignin or murein.

The nucleus is the obligatory organelle of eukaryotes. In it there is a hereditary material - DNA, having the form of chromosomes. Bacteria and cyanobacteria contain a nucleoid that serves as a carrier of deoxyribonucleic acid. All of them perform strictly specific functions that cause metabolic cellular processes.

What do we mean by the term "cellular nutrition"

Life manifestations of a cell are nothing more than the transfer of energy and its transformation from one species to another (according to the first law of thermodynamics). Energy, which is in nutrients in a latent, i.e., bound state, passes into ATP molecules. On the question of what is cell nutrition in biology, there is a response that takes into account the following postulates:

1. The cell, being an open biosystem, requires a constant inflow of energy from the external environment.
2. Organic substances needed for nutrition, the cell can get two ways:

A) from the intercellular environment, in the form of ready-made compounds;

B) independently synthesizing proteins, carbohydrates and fats from carbon dioxide, ammonia, etc.

Therefore, all organisms are divided into heterotrophic and autotrophic, the metabolism of which is studied by biochemistry.

Metabolism and energy

Organic substances entering the cell are split, resulting in the release of energy in the form of ATP or NADP-H2 molecules. The whole set of reactions of assimilation and dissimilation is metabolism. Below we will consider the stages of energy exchange, providing nutrition of heterotrophic cells. First, proteins, carbohydrates and lipids split to their monomers: amino acids, glucose, glycerol and fatty acids. Then, during anoxic cleavage, they undergo further decomposition (anaerobic digestion).

In this way, nutrition of intracellular parasites occurs: rickettsia, chlamydia and pathogenic bacteria, for example, clostridia. Unicellular yeast fungi split glucose to ethanol, lactobacillus bacteria - to lactic acid. Thus, glycolysis, alcohol, oleaginous acid, lactic acid fermentation are examples of cell nutrition due to anaerobic cleavage in heterotrophs.

Autotrophy and features of metabolic processes

For organisms living on Earth, the main source of energy is the Sun. Thanks to him, the needs of the inhabitants of our planet are provided. Some of them synthesize nutrients due to light energy, they are called phototrophs. Others - using the energy of oxidation-reduction reactions, they are called chemotropics. In unicellular algae, the nutrition of the cell, the photo of which is presented below, is photosynthetic.

Green plants contain chlorophyll, which is part of the chloroplasts. It plays the role of an antenna that captures quanta of light. In the light and dark phases of photosynthesis, enzymatic reactions occur (the Calvin cycle), the result of which is the formation of carbonic acid from all organic substances used for nutrition. Therefore, the cell, which is powered by the use of light energy, is called autotrophic or phototrophic.

Unicellular organisms, called chemosynthetic organisms, use the energy liberated by chemical reactions to form organic substances, for example, iron bacteria oxidize ferrous compounds to a trivalent iron, and the released energy goes to the synthesis of glucose molecules.

Thus, photo-synthetic organisms capture light energy and convert it into energy of covalent bonds of mono- and polysaccharides. Then, through the links of the supply chains, energy is transferred to cells of heterotrophic organisms. In other words, thanks to photosynthesis, all the structural elements of the biosphere exist. It can be said that a cell that feeds autotrophically, feeds not only itself, but everything that lives on planet Earth.

How do heterotrophic organisms feed?

The cell, the food of which depends on the intake of organic substances from the external environment, is called heterotrophic. Such organisms as fungi, animals, humans, as well as parasitic bacteria, break down carbohydrates, proteins and fats with the help of digestive enzymes.

Then the resulting monomers are absorbed by the cell and used by it to build its organelles and vital functions. Dissolved nutrients enter the cell by pinocytosis, and solid food particles - phagocytosis. Heterotrophic organisms can be divided into saprotrophs and parasites. The first (for example, soil bacteria, fungi, some insects) feed on dead organics, the latter (pathogenic bacteria, helminths, parasitic fungi) - cells and tissues of living organisms.

Mixotrophs, their spread in nature

Mixed type of food in nature is rare enough and is a form of adaptation (idioadaptation) to various factors of the environment. The main condition of mixotrophy is the presence of cells and organelles containing chlorophyll for photosynthesis and a system of enzymes that break down the finished nutrients coming from the environment. For example, the unicellular animal euglena green contains in the hyaloplasm chromatophores with chlorophyll.

When the reservoir in which euglena lives is well lit, it eats like a plant, i.e. autotrophically, by photosynthesis. As a result, glucose is synthesized from carbon dioxide, which the cell uses as food. At night, euglena feeds heterotrophically, splitting organic substances with enzymes in the digestive vacuoles. Thus, scientists consider the mixotrophic nutrition of the cell as evidence of the unity of the origin of plants and animals.

Growth of the cell and its relationship with trophism

The increase in length, mass, volume of both the whole organism and its individual organs and tissues is called growth. It is impossible without the constant entry into the cells of nutrients serving as building material. To get an answer to the question of how the cell grows, the nutrition of which occurs autotrophically, it is necessary to clarify whether it is an independent organism or it enters as a structural unit in the multicellular organism. In the first case, growth will occur during the interphase of the cell cycle. The processes of plastic exchange are intensively occurring in it. The nutrition of heterotrophic organisms is correlated with the presence of food coming from the external environment. The growth of a multicellular organism is due to the activation of biosynthesis in educational tissues, as well as the predominance of anabolic reactions over the processes of catabolism.

The role of oxygen in the nutrition of heterotrophic cells

Aerobic organisms: some bacteria, fungi, animals and humans use oxygen to completely break down nutrients, such as glucose, to carbon dioxide and water (the Krebs cycle). It occurs in the mitochondrial matrix containing the enzymatic system H + -ATP-ase, which synthesizes ATP molecules from ADP. In prokaryotic organisms, such as aerobic bacteria and cyanobacteria, the oxygen stage of dissimulation occurs on the plasma membrane of cells.

Specificity of food gamete

In molecular biology and cytology, the nutrition of a cell can be briefly described as the process of the intake of nutrients into it, their splitting and the synthesis of a certain portion of energy in the form of ATP molecules. The trophic gametes: ovules and spermatozoa, has some peculiarities associated with the high specificity of their functions. This is especially true of the female sex cell, which is forced to accumulate a large supply of nutrients, mainly in the form of yolk.

After fertilization, she will use them to crush and form the embryo. Spermatozoa in the process of maturation (spermatogenesis) receive organic substances from Sertoli cells located in the seminiferous tubules. Thus, both types of gametes have a high level of metabolism, which is possible, thanks to active cell trophism.

The role of mineral nutrition

The processes of metabolism are impossible without the influx of cations and anions, which are part of the mineral salts. For example, magnesium ions are necessary for photosynthesis, for the operation of the mitochondrial enzyme systems - potassium and calcium ions, the presence of sodium ions, as well as anions of carbonate acid, to preserve the buffer properties of the hyaloplasm. Solutions of mineral salts enter the cell by pinocytosis or diffusion through the cell membrane. Mineral nutrition is inherent in both autotrophic and heterotrophic cells.

Summing up, we were convinced that the value of cell nutrition is really great, because this process leads to the formation of building material (carbohydrates, proteins and fats) from carbon dioxide in autotrophic organisms. Heterotrophic cells feed on organic substances formed as a result of vital activity of autotrophs. They use the received energy for reproduction, growth, movement and other processes of vital activity.