Proteins are the most important organic substancesthe number of which prevails over all other macromolecules that are present in the living cell. They make up more than half the weight of the dry matter of both plant and animal organisms. The functions of proteins in the cell are diverse, some of them are still unknown to science. But still the main directions of their "work" are well studied. Some are needed in order to stimulate the processes occurring in cells and tissues. Others transfer important mineral compounds through the cell membrane and through the blood vessels from one organ to another. Some protect the body from often alien pathogenic agents. One thing is clear - without proteins, not a single process in our body proceeds.
The functions of proteins in the body are diverse.Each group has a specific chemical structure, performs one specialized "work". In some cases, several types of proteins are interconnected with each other. They are responsible for the different stages of the same process. Or they affect several at once. For example, the regulatory function of proteins is carried out by enzymes and hormones. This phenomenon can be imagined, remembering the hormone adrenaline. It is produced by the adrenal medulla. By entering the blood vessels, it increases the amount of oxygen in the blood. Blood pressure rises, sugar content increases. It stimulates metabolic processes. Adrenaline is also a mediator of the nervous system in fish, amphibians and reptiles.
Numerous flowing in the cells of the livingOrganisms biochemical reactions are carried out at high temperatures and with a neutral pH. In such conditions, the speed of their passage is too low, so we need specialized catalysts, called enzymes. All their diversity is combined into 6 classes, which differ in the specificity of the action. Enzymes are synthesized on the ribosomes in the cells. Their study is engaged in the science of Enzymology.
Undoubtedly, regulatory enzymes are impossible without enzymes.protein function. They have a high selectivity of action. Their activity can be regulated by inhibitors and activators. In addition, enzymes usually exhibit substrate specificity. Also, the enzymatic activity depends on the conditions in the body and in the cells in particular. Their flow is affected by pressure, acidic pH, temperature, ionic strength of the solution, that is, the concentration of salts in the cytoplasm.
The cage must constantly receive the necessarybody mineral and organic matter. They are needed as building materials and energy sources in cells. But the mechanism of their receipt is rather complicated. Cell membranes are not only protein. Biological membranes are built on the principle of a double layer of lipids. Between them are various proteins. It is very important that the hydrophilic sites are on the surface of the membrane, and the hydrophobic ones are in its thickness. Thus, such a structure makes the shell impenetrable. Through it they cannot independently, without “help”, pass such important components as sugars, metol ions and amino acids. Specialized proteins, which are inserted into the lipid layers, transport them through the cytoplasmic membrane into the cytoplasm.
But the transport function of proteins is notonly between the extracellular substance and the cell. Some substances important for physiological processes have to be delivered from one organ to another. For example, blood transport protein is serum albumin. It is endowed with the unique ability to form compounds with fatty acids, which appear during the digestion of fats, with drugs, as well as with steroid hormones. Hemoglobin (delivering oxygen molecules), transferrin (combining with iron ions) and ceruplazmin (forming complexes with copper) are important carrier proteins.
Great value in the course of physiologicalprocesses in multicellular complex organisms have receptor proteins. They are mounted in the plasma membrane. They serve for perception and decoding of various kinds of signals, which in a continuous stream enter the cells not only from neighboring tissues, but also from the external environment. At present, perhaps the most studied receptor protein is acetylcholine. It is located in a number of interneuronic contacts on the cell membrane.
But the signaling function of proteins is not carried out.just inside the cells. Many hormones bind to specific receptors on their surface. This formed connection is a signal that activates the physiological processes in the cells. An example of such proteins is insulin acting in the adenylate cyclase system.
The functions of proteins in the cell are different.Some of them are involved in immune responses. It protects the body from infections. The immune system is able to respond to the identified foreign agents by synthesizing a huge number of lymphocytes. These substances are capable of selectively damaging these agents, they may be foreign to the body, such as bacteria, supramolecular particles, or it may be cancer cells.
One of the groups - "beta" lymphocytes - producesproteins that enter the bloodstream. They have a very interesting function. These proteins must recognize foreign cells and macromolecules. Then they connect with them, forming a complex that is subject to destruction. These proteins are called immunoglobulins. The foreign components themselves are antigens. And the immunoglobulins that correspond to them are antibodies.
In the body, in addition to highly specialized,there are also structural proteins. They are necessary to provide mechanical strength. These functions of proteins in the cell are important for maintaining the shape and preserving the body's youth. The most famous is collagen. It is the main protein of the extracellular matrix of connective tissues. In higher mammals, it is up to 1/4 of the total mass of proteins. Collagen is synthesized in fibroblasts, which are the main cells of connective tissues.
Such functions of proteins in the cell have enormousvalue. In addition to collagen, another structural protein is known - elastin. It is also a component of the extracellular matrix. Elastin is able to give the fabric the ability to stretch within certain limits and easily return to its original form. Another example of a structural protein is fibroin, which is found in silkworm caterpillars. This is the main component of silk thread.
The role of proteins in the cell can not be overemphasized.They take part in the work of the muscles. Muscle contraction is an important physiological process. As a result, ATP stored in the form of macromolecules is converted into chemical energy. Two proteins, actin and myosin, are directly involved in the process.
These motor proteins arefilamentous molecules that function in the contractile system of skeletal muscles. They are also found in non-muscle tissues in eukaryotic cells. Another example of motor proteins is tubulin. Microtubules are constructed from it, which are an important element of the flagella and cilia. Also, microtubules containing tubulin are found in the cells of the nervous tissue of animals.
The protective role of proteins in the cell is enormous.In part, it is placed on a group that is commonly called antibiotics. These are substances of natural origin, which are synthesized, as a rule, in bacteria, microscopic fungi and other microorganisms. They are aimed at suppressing the physiological processes of other competing organisms. Antibiotics of protein origin were discovered in the 40s. They made a revolution in medicine, giving it a powerful impetus to development.
By their chemical nature, antibiotics are highlydiverse group. They differ in the mechanism of action. Some interfere with the synthesis of protein inside the cells, the second block the production of important enzymes, the third inhibit growth, the fourth - reproduction. For example, the well-known streptomycin interacts with bacterial cell ribosomes. Thus, the synthesis of proteins is slowed down in them. However, these antibiotics do not interact with eukaryotic ribosomes of the human body. This means that for higher mammals these substances are non-toxic.
This is not all the functions of proteins in the cell.The table of antibiotic substances makes it possible to determine other highly specialized actions that these specific natural compounds can have on bacteria and not only. Currently, studies are underway on antibiotics of protein origin, which, when interacting with DNA, violate the processes associated with the embodiment of hereditary information. But while such substances are used only in chemotherapy of oncological diseases. An example of such an antibiotic substance is dactinomycin, synthesized by actinomycetes.
Proteins in the cell perform a veryspecific and even extraordinary. A number of living organisms produce toxic substances - toxins. By nature, these are proteins and complex low molecular weight organic compounds. As an example, the poisonous pulp of the fungus is a pale grebe.
Some proteins perform the function of providingnutrition of embryos of animals and plants. There are many such examples. The value of protein in the cell of cereal seeds lies precisely in this. They will feed the emerging germ of a plant in the early stages of its development. In animals, food proteins are egg albumin and milk casein.
The above examples are only the part thatsufficiently studied. But in nature there are many mysteries. Proteins in the cage of many species are unique, and now it is even difficult to classify them. For example, monellin is a protein found and isolated from an African plant. It tastes sweet, but does not cause obesity and is not toxic. In the future it may be an excellent substitute for sugar. Another example is a protein found in some arctic fish that prevents blood from freezing, acting as antifreeze in the literal sense of this comparison. A number of insects in the wing compounds revealed a resilin protein, which has a unique, almost perfect elasticity. And this is not all examples of substances that are yet to be studied and classified.
