Proteins are the most important organic substances, the number of which prevails over all other macromolecules that are present in a living cell. They make up more than half of the dry matter weight 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 carry important mineral compounds across the cell membrane and through the blood vessels from one organ to another. Some protect the body from foreign often pathogenic agents. One thing is clear - not a single process in our body takes place without proteins.
Basic functions of proteins
The functions of proteins in the body are diverse. Each group has a specific chemicalbuilding, performs one specialized "work". In some cases, several types of proteins are interconnected with each other. They are responsible for 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 by remembering the hormone adrenaline. It is produced by the adrenal medulla. Entering the blood vessels, it increases the amount of oxygen in the blood. The blood pressure also rises, the sugar content increases. This stimulates metabolic processes. Adrenaline is also a neurotransmitter in fish, amphibians and reptiles.
Enzymatic function
Many biochemical reactions occurring in the cells of living organisms are carried out at high temperatures and with a neutral pH value. Under such conditions, the rate of their passage is too low, so specialized catalysts called enzymes are needed. All their diversity is combined into 6 classes, which differ in the specificity of the action. Enzymes are synthesized on ribosomes in cells. The science of enzymology is engaged in their study.
Undoubtedly, the regulatory function of proteins is impossible without enzymes. They have a high selectivity of action. Their activity can be regulated by inhibitors and activators. In addition, enzymes usually exhibit substrate specificity. Also, enzymatic activity depends on the conditions in the body and in cells in particular. Their flow is affected by pressure, acidic pH, temperature, ionic strength of the solution, that iss alt concentration in the cytoplasm.
Protein transport function
The cell must constantly receive the necessary mineral and organic substances for the body. They are needed as building materials and energy sources in cells. But the mechanism of their receipt is quite complicated. Cell walls are made up of more than just proteins. Biological membranes are built on the principle of a double layer of lipids. Various proteins are embedded between them. It is very important that the hydrophilic regions are located on the surface of the membrane, while the hydrophobic regions are located in its thickness. Thus, such a structure makes the shell impenetrable. They cannot pass through it on their own, without "help", such important components as sugars, metol ions and amino acids. They are transported through the cytoplasmic membrane to the cytoplasm by specialized proteins that are embedded in lipid layers.
Transport of substances from one organ to another
But the transport function of proteins is carried out not only between the intercellular substance and the cell. Some substances important for physiological processes have to be delivered from one body to another. For example, the transport protein in the blood is serum albumin. It is endowed with a unique ability to form compounds with fatty acids that appear during the digestion of fats, with drugs, as well as with steroid hormones. Important carrier proteins are hemoglobin (delivering oxygen molecules), transferrin (combining with iron ions) and ceruplasmin (forming complexes withcopper).
Signal function of proteins
Receptor proteins are of great importance in the course of physiological processes in multicellular complex organisms. They are embedded in the plasma membrane. They serve to perceive and decipher various kinds of signals that enter the cells in a continuous stream not only from neighboring tissues, but also from the external environment. Currently, perhaps the most studied receptor protein is acetylcholine. It is located in a number of interneuronal junctions on the cell membrane.
But the signaling function of proteins is carried out not only inside the cells. Many hormones bind to specific receptors on their surface. Such a formed compound is a signal that activates physiological processes in cells. An example of such proteins is insulin, which acts in the adenylate cyclase system.
Protection function
The functions of proteins in a cell are different. Some of them are involved in immune responses. This protects the body from infections. The immune system is able to respond to the identified foreign agents with the synthesis of a huge number of lymphocytes. These substances can selectively damage these agents, they can be foreign to the body, such as bacteria, supramolecular particles, or they can be cancer cells.
One of the groups - "beta"-lymphocytes - produces proteins 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 to be destroyed. These proteins are called immunoglobulins. The foreign components themselves are antigens. And the immunoglobulins that correspond to them are antibodies.
Structural function
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 body's shape and 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 are of great importance. In addition to collagen, another structural protein is known - elastin. It is also a constituent of the extracellular matrix. Elastin is able to give fabrics the ability to stretch within certain limits and easily return to their original shape. Another example of a structural protein is fibroin, which is found in silkworm caterpillars. It is the main component of silk threads.
Motor proteins
The role of proteins in the cell cannot be overestimated. They also take part in the work of muscles. Muscle contraction is an important physiological process. As a result, the ATP stored in the form of macromolecules is converted into chemical energy. The direct participants in the process are two proteins - actin and myosin.
These motor proteinsare filamentous 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 built from it, which are an important element of flagella and cilia. Microtubules containing tubulin are also found in the cells of the nervous tissue of animals.
Antibiotics
The protective role of proteins in the cell is enormous. Part of it is assigned to 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 revolutionized medicine, giving it a powerful impetus to development.
By their chemical nature, antibiotics are a very diverse group. They also differ in their mechanism of action. Some prevent protein synthesis inside cells, others block the production of important enzymes, others inhibit growth, and others inhibit reproduction. For example, the well-known streptomycin interacts with the ribosomes of bacterial cells. Thus, they dramatically slow down the synthesis of proteins. At the same time, these antibiotics do not interact with eukaryotic ribosomes of the human body. This means that these substances are not toxic to higher mammals.
This is not all the functions of proteins in the cell. Tableantibiotic substances allows you to determine other highly specialized actions that these specific natural compounds are able to have on bacteria and not only. Currently, antibiotics of protein origin are being studied, which, when interacting with DNA, disrupt the processes associated with the embodiment of hereditary information. But so far, such substances are used only in the chemotherapy of oncological diseases. An example of such an antibiotic substance is dactinomycin, synthesized by actinomycetes.
Toxins
Proteins in a cell perform a very specific and even extraordinary function. A number of living organisms produce toxic substances - toxins. By their nature, these are proteins and complex low molecular weight organic compounds. An example is the poisonous pulp of the fungus pale grebe.
Reserve and food proteins
Some proteins perform the function of providing nutrition to the embryos of animals and plants. There are many such examples. The importance of protein in the cell of cereal seeds lies precisely in this. They will nourish the emerging germ of the plant in the first stages of its development. In animals, the dietary proteins are egg albumin and milk casein.
Unexplored properties of proteins
The above examples are only the part that has already been sufficiently studied. But in nature there are many mysteries. Proteins in the cell of many biological species are unique, and at present even classify themdifficult. For example, monellin is a protein discovered and isolated from an African plant. It tastes sweet, but is non-obese and non-toxic. In the future, it may be an excellent substitute for sugar. Another example is a protein found in some arctic fish that prevents the blood from freezing by acting as antifreeze in the literal sense of the comparison. In a number of insects, the resilin protein, which has a unique, almost perfect elasticity, was found in the wing joints. And these are not all examples of substances that are yet to be studied and classified.
