Proteins are the most important organic substances, the amount of which prevails over all other macromolecules that are present in a living cell. They make up more than half 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 taking place in cells and tissues. Others carry important mineral compounds across the cell membrane and blood vessels from one organ to another. Some protect the body against alien often pathogenic agents. One thing is clear - without proteins, not a single process in our body proceeds.
The main functions of proteins
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. They are responsible for the different stages of one 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 recalling the hormone adrenaline. It is produced by the adrenal medulla. Entering the blood vessels, it increases the amount of oxygen in the blood. Blood pressure rises, sugar content increases. This stimulates metabolic processes. Adrenaline is also a mediator of the nervous system in fish, amphibians and reptiles.
Enzymatic function
Numerous biochemical reactions taking place in the cells of living organisms are carried out at high temperatures and with a neutral pH value. Under such conditions, the speed of their passage is too low, therefore, specialized catalysts called enzymes are needed. All their diversity is combined in 6 classes, which differ in the specificity of the action. Enzymes are synthesized on ribosomes in cells. Enzymology studies them.
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 specificity for substrates. Enzymatic activity also depends on the conditions in the body and in the cells in particular. Their course is affected by pressure, acid pH, temperature, ionic strength of the solution, that is, the concentration of salts in the cytoplasm.
Protein Transport Function
Mineral and organic substances necessary for the body must constantly enter the cell. They are needed as building materials and energy sources in cells. But the mechanism of their receipt is quite complicated. Cell membranes are not only made up of proteins. Biological membranes are built on the principle of a double layer of lipids. Between them various proteins are built. It is very important that hydrophilic sites are on the surface of the membrane, and hydrophobic in its thickness. Thus, such a structure makes the shell impervious. Such important components as sugars, metol ions, and amino acids cannot pass through it on their own, without “help”. Specialized proteins are transported through the cytoplasmic membrane into the cytoplasm, which are mounted in the layers of lipids.
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 organ to another. For example, blood transport protein is serum albumin. He is endowed with a unique ability to form compounds with fatty acids that appear during the digestion of fats, with drugs, and also with steroid hormones. Important carrier proteins are hemoglobin (delivering oxygen molecules), transferrin (combining with iron ions) and ceruplasmin (forming complexes with copper).
Signal function of proteins
Protein receptors are of great importance in the course of physiological processes in multicellular complex organisms. They are mounted in a plasma membrane. They serve for the 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 interneuronal contacts 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 acting in the adenylate cyclase system.
Protective function
The functions of proteins in the cell are different. Some of them are involved in immune responses. This protects the body against infections. The immune system is able to respond to 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, for example bacteria, supramolecular particles, or they may be cancer cells.
One of the groups - "beta" lymphocytes - produces proteins that enter the bloodstream. They have a very interesting feature. 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. Alien 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 shape and maintaining the body's youth. The most famous is collagen. This is the main protein of the extracellular matrix of connective tissues. In higher mammals, it makes up to 1/4 of the total mass of proteins. Collagen is synthesized in fibroblasts, which are the main cells of connective tissue.
Such protein functions in the cell are of great importance. In addition to collagen, another structural protein is known - elastin. It is also a component of the extracellular matrix. Elastin is able to give tissues the ability to stretch within certain limits and easily return to their original form. Another example of a structural protein is fibroin, which is found in silkworm caterpillars. This is the main component of silk threads.
Motor proteins
The role of proteins in the cell cannot be overestimated. They take part in the work of muscles. Muscle contraction is an important physiological process. As a result, the ATP stored as macromolecules is converted into chemical energy. The direct participants in the process are two proteins - actin and myosin.
These motor proteins are filiform 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. Partially, 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. Protein-derived antibiotics 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 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 the growth, the fourth reproduction. For example, well-known streptomycin interact with bacterial cell ribosomes. Thus, protein synthesis drastically slows 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 not toxic.
These are far from all the functions of proteins in the cell. The table of antibiotic substances allows us to determine other highly specialized actions that these specific natural compounds are able to exert on bacteria and not only. Currently, studies are being conducted on protein-derived antibiotics, which, when interacting with DNA, disrupt the processes associated with the embodiment of hereditary information. But while such substances are used only for chemotherapy of oncological diseases. An example of such an antibiotic substance is dactinomycin synthesized by actinomycetes.
Toxins
Proteins in the cell perform a very specific and even extraordinary function. 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 flesh of a mushroom is a pale toadstool.
Spare and food proteins
Some proteins perform the function of providing nutrition to the 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 nourish the emerging germ of the plant in the first stages of its development. In animals, edible proteins are egg albumin and milk casein.
Unexplored properties of proteins
The above examples are just 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 now it is difficult to even classify them. For example, monellin is a protein discovered and isolated from an African plant. It tastes sweet, but it does not cause obesity and is not toxic. In the future, it could be an excellent substitute for sugar. Another example is the protein found in some arctic fish, it prevents blood freezing, acting as antifreeze in the literal sense of this comparison. In a number of insects, the resilin protein, which has a unique, almost ideal elasticity, was detected in the wing compounds. And these are not all examples of substances that have yet to be studied and classified.