The supranembrane complexes of plant cells, fungi, and some bacteria include such a structure as their wall. In this article, we will study the structure of the cell membrane in various groups of organisms, as well as the functions that it performs. As you know, this component was first discovered by the English scientist Robert Hooke in the 17th century. We also note that the cell membrane is absent in unicellular animals and multicellular organisms, ranging from intestinal and ending with vertebrates: fish, amphibians, reptiles, birds and mammals.
Why is she needed
Despite the fact that the structure and chemical composition of the wall of fungi, plants, and pellets are not the same, the functions of the cell membrane are very similar. First of all, it is the protection of the cytoplasm and its organelles from the damaging effects of environmental factors.
Further: the supramembrane complex serves as a reliable support and ensures the strength of contacts in the tissues of plants and fungi. Below we will consider in more detail how the shell structure is interconnected with the functions that it performs.
Features of the cell wall of plants
This structure in plant organisms consists mainly of a polymer belonging to the class of polysaccharides - cellulose. Its molecular formula is the same as that of plant starch (C 6 H 10 O 5 ) n . The macromolecules of this polysaccharide contain beta-glucose residues and have only a linear structure, so they can form fibers that are bundled. They form a strong cell wall framework , recessed into the colloidal matrix, which also consists mainly of carbohydrates - pectin and hemicellulose. Also, cellulose is often found in other parts of plants, for example, cotton fibers are 99% pure pulp, flax and hemp contain it in an amount of 75-80%, in wood - up to 55%. As mentioned earlier, the functions of the cell membrane are determined by the tissue of which organisms it enters.
In addition to cellulose, the wall contains proteins, lipids and inorganic substances. For example, the cell walls of higher spore plants - horsetail - contain silicon dioxide, so the plant itself is very stiff and durable and is inedible for animals. One of the layers forming the stem of perennials and called the cork, accumulates a fat-like substance in the shells - suberin. As a result of this, the cytoplasm and its organoids are destroyed, and the cells themselves can only perform a supporting function (stem sampling).
If lignin accumulates between cellulose fibers, it, together with hemicellulose, enhances the mechanical strength of the stems and trunks of tree species, and the pigments contained in lignin determine the color of the wood. The wall also contains pores lined with a membrane that allow the transport of substances.
The structure and functions of the cell membrane of fungi
In representatives of various groups of fungi, the basis of the wall is chitin, a polysaccharide that is also found in the external skeleton of arthropods and in some bacteria. The supmembrane complexes of fungi also contain cellulose and animal starch - glycogen. For example, the chemical structure of the cell wall of yeast is represented mainly by carbohydrates - glucan and mannan. The wall itself is quite strong and poorly digested in the gastrointestinal tract of animals, so the nutrients of the yeast are inaccessible and are not absorbed by the epithelium of the small intestine.
Bacteria features
If the cell membrane is absent in the protist, then in prokaryotes it has a very complex structure, including murein, lipoproteins and lipopolysaccharides, as well as teichoic acids. Wall lipopolysaccharides promote the adhesion of bacteria to various substrates: for example, to tooth enamel or to eukaryotic membranes. Therefore, the cell membrane of bacteria also has antigenic properties.
Often the wall of bacteria on top is covered with a mucous capsule (capsid), over which another protective layer can be located - peplos. Depending on its structure, in microbiology all bacteria are divided into gram-positive and gram-negative.
Differentiation of bacteria according to biochemical composition
The method that made it possible to distinguish prokaryotes by the peculiarities of the chemical structure of their shell was proposed by the Danish scientist G. Gram at the end of the 19th century. He found that some types of bacteria stain well with aniline dyes and form persistent violet compounds that make up the cell wall.
Such prokaryotes were called gram-positive: for example, staphylococci and streptococci. All of them are sensitive to antibiotics of a number of penicillin and actinomycin. Other bacteria called gram-negative do not stain with methyl violet. They are resistant to penicillin, as they have a strong capsule and low-permeable cell wall. These include salmonella, shigella, helicobacter. The cell membrane of bacteria, having a different chemical composition, serves as an important microbiological characteristic, which is taken into account in pharmacology and medicine.
Features of mycoplasmas
Let us dwell on a group of very small bacteria - mycoplasmas. Microscopic studies have shown that they do not have a cell membrane, therefore mycoplasmas are sensitive to certain antibiotics, for example, tetracycline. Mycoplasmas are widespread in nature, are the causative agents of many diseases, including the human urogenital system.
Most mycoplasmas in their metabolism necessarily use oxygen and are strict aerobes. Being parasites of humans and mammals, they multiply rapidly, since cholesterol is present in the composition of cell membranes, which is a favorable substrate for the growth and reproduction of mycoplasmas.
Adaptations in the simplest
Earlier, we noted the fact that the cell membrane is absent in ciliates and other unicellular animals, for example, in the roots. Zoologists have established that protists are a full-fledged animal organism, which is characterized by all functions: growth, reproduction, nutrition, respiration, and excretion. Moreover, living in an aquatic environment or moist soil, protists through a thin membrane transport water and mineral salts in the environment, and release products of their own metabolism through plasma membrane pores. Therefore, unicellular animals do not have complex supranembrane complexes, which is an idioadaptation to the peculiarities of environmental conditions.
To protect and preserve the integrity of the shell, protozoa have a pelicule - an outer more dense layer of ectoplasm. Thanks to the pelicule, which has elasticity and strength, a constant shape of the animal’s body is maintained.
In this article, we studied the structure and chemical composition of the cell membrane characteristic of cells of plant organisms, as well as bacteria and fungi.