Proteins: a biological role. The biological role of protein in the body

Proteins, whose biological role will be considered today, are high-molecular compounds constructed from amino acids. Among all other organic compounds, they are among the most complex in their structure. By elemental composition, proteins differ from fats and carbohydrates: besides oxygen, hydrogen and carbon, they also contain nitrogen. In addition, an essential part of the most important proteins is sulfur, and some contain iodine, iron and phosphorus.

The biological role of the protein is very great. It is these compounds that make up the bulk of the protoplasmic mass, as well as the nuclei of living cells. In all animal and plant organisms are proteins.

One or more functions

The biological role and functions of their various compounds are different. As a substance having a specific chemical structure, each protein performs a highly specialized function. Only in some cases it can perform several interrelated ones. For example, adrenaline, which is produced in the adrenal medulla, entering the blood, increases blood pressure and oxygen consumption, the sugar content in the blood. In addition, he is a stimulant of metabolism, and in cold-blooded animals - and a mediator of the nervous system. As you can see, it performs many functions at once.

Enzymatic (catalytic) function

The diverse biochemical reactions taking place in living organisms are carried out under mild conditions, at which the temperature is close to 40 ° C, and the pH values are practically neutral. Under these conditions, the flow rates of many of them are negligible. Therefore, in order for them to be realized, enzymes are needed-special biological catalysts. Almost all reactions, except photolysis of water, are catalyzed in living organisms by enzymes. These elements are either proteins or complexes of proteins with cofactor (organic molecule or metal ion). Enzymes act very selectively, launching the necessary process. So, the catalytic function, considered above, is one of those that carry out proteins. The biological role of these compounds, however, is not limited to its fulfillment. There are many other functions that we will consider below.

Transport function

For the existence of a cell, it is necessary that many substances enter its interior, which provide it with energy and building material. All biological membranes are built on the general principle. This is a double layer of lipids, proteins are immersed in it. At the same time, hydrophilic regions of macromolecules are concentrated on the surface of membranes, and hydrophobic "tails" in the thickness of them. This structure remains impenetrable for important components: amino acids, sugars, alkali metal ions. The penetration of these elements into the cell occurs via transport proteins that are embedded in the cell membrane. Bacteria, for example, have a special protein that provides the transfer of lactose (milk sugar) through the outer membrane.

Multicellular organisms have a system for transporting various substances from one organ to another. This is primarily about hemoglobin (pictured above). In blood plasma, in addition, there is always serum albumin (transport protein). It has the ability to form strong complexes with fatty acids formed during digestion of fats, as well as with a number of hydrophobic amino acids (for example, with tryptophan) and with many medicinal preparations (some penicillins, sulfonamides, aspirin). Transferrin, which provides the transfer in the body of iron ions, is another example. You can also mention ceruplasmin, which carries copper ions. So, we looked at the transport function that proteins perform. Their biological role is very important from this point of view.

The receptor function

Protein receptors are of great importance, especially to ensure the vital activity of multicellular organisms. They are built into the plasma membrane and serve to perceive and further transform the signals that enter the cell. In this case, the signals can be both from other cells and from the environment. Acetylcholine receptors are currently most studied. They are in a series of interneuronal contacts on the cell membrane, including in neuromuscular junctions, in the cerebral cortex. These proteins interact with acetylcholine and transmit the signal inside the cell.

The neurotransmitter must be removed to receive the signal and its transformation in order for the cell to be able to prepare for the perception of further signals. For this, acetylcholinesterase is used, a special enzyme that catalyzes the hydrolysis of acetylcholine to choline and acetate. Is not it really important, and the receptor function that proteins perform? The biological role of the next, protective function, is enormous for the body. With this just can not disagree.

Protective function

In the body, the immune system responds to the appearance in it of foreign particles by the production of a large number of lymphocytes. They are able to damage elements selectively. Such foreign particles can be cancer cells, pathogenic bacteria, supramolecular particles (macromolecules, viruses, etc.). B-lymphocytes are a group of lymphocytes that produce specific proteins. These proteins are released into the circulatory system. They recognize foreign particles, while forming a highly specific complex at the stage of destruction. These proteins are called immunoglobulins. Antigens are called foreign substances that cause the immune system to respond.

Structural function

In addition to proteins that perform highly specialized functions, there are also those whose significance is mainly structural. Thanks to them, mechanical strength is provided, as well as other properties of tissues of living organisms. To such proteins belongs, first of all, collagen. Collagen (in the photo, see below) in mammals is about a quarter of the mass of proteins. It is synthesized in the main cells, of which the connective tissue consists (they are called fibroblasts).

Initially, collagen is formed as procollagen - its precursor, which undergoes chemical treatment in fibroblasts. Then it is formed in the form of three polypeptide chains twisted into a spiral. They combine already outside fibroblasts into collagen fibrils several hundred nanometers in diameter. The latter form collagen filaments, which can already be seen under a microscope. In the elastic tissues (walls of the lungs, blood vessels, in the skin), the extracellular matrix, in addition to collagen, also contains the elastin protein. It can stretch in a fairly wide range and then return to its original state. Another example of a structural protein that can be mentioned here is fibroin silk. It is isolated during the formation of the pupa of the silkworm caterpillar. This is the main component of silk threads. We now turn to the description of motor proteins.

Motor proteins

And in the implementation of motor processes, the biological role of proteins is great. Let us briefly describe this function. Muscle contraction is a process during which chemical energy is converted into mechanical work. Its immediate participants are two proteins - myosin and actin. Myosin has a very unusual structure. It is formed of two globular heads and a tail (a long thread-like part). About 1600 nm is the length of one molecule. The share of heads in this case is about 200 nm.

Actin (pictured above) is a globular protein with a molecular weight of 42,000. It can polymerize to form a long structure, and interact in this form with the myosin head. An important feature of this process is its dependence on the presence of ATP. If its concentration is high enough, the complex formed by myosin and actin is destroyed, and then it is restored after the hydrolysis of ATP as a result of the action of myosin ATPase. This process can be observed, for example, in a solution in which both proteins are present. It becomes viscous as a result of the formation of a high-molecular complex in the absence of ATP. When it is added, the viscosity is sharply reduced due to the destruction of the complex created, after which it gradually begins to recover as a result of the hydrolysis of ATP. In the process of muscle contraction, these interactions play a very large role.

Antibiotics

We continue to disclose the theme "The biological role of protein in the body." A very large and very important group of natural compounds are substances called antibiotics. They are of microbial origin. These substances are released by special types of microorganisms. The biological role of amino acids and proteins is indisputable, however, antibiotics perform a special, very important function. They inhibit the growth of microorganisms that compete with them. In the 1940s, the discovery and use of antibiotics produced a real revolution in the treatment of infectious diseases caused by bacteria. It should be noted that antibiotics do not work for viruses in most cases, so using them as antiviral drugs is ineffective.

Examples of antibiotics

The penicillin group was first put into practice. Examples of this group are ampicillin and benzylpenicillin. Antibiotics in the mechanism of action and chemical nature are diverse. Some of those that are widely used today interact with human ribosomes, while protein synthesis is inhibited in bacterial ribosomes. At the same time, they hardly interact with eukaryotic ribosomes. Therefore, for bacterial cells they are fatal, but for animals and humans are not very toxic. These antibiotics include streptomycin and levomycetin (chloramphenicol).

The biological role of protein biosynthesis is very important, and the process itself has several stages. We will talk about it only in general terms.

The process and biological role of protein biosynthesis

This process is multistage and very complex. It occurs in ribosomes - special organelles. There are many ribosomes in the cell. In Escherichia coli, for example, there are about 20 thousand.

"Describe the process of protein biosynthesis and its biological role" - this task many of us received at school. And for many it caused difficulties. Well, let's try to figure it out together.

The protein molecules are polypeptide chains. They are, as you already know, from individual amino acids. However, the latter are not sufficiently active. In order to connect and form a protein molecule, they need activation. It occurs as a result of the action of special enzymes. Each amino acid has its own enzyme, specifically tuned to it. The source of energy for this process is ATP (adenosine triphosphate). Amino acid as a result of activation becomes more labile and binds under the action of this enzyme with t-RNA, which transfers it to the ribosome (because of this, this RNA is called transport). In the ribosome, thus activated, activated amino acids are connected to the tRNA. The ribosome is a kind of conveyor for assembling from the incoming amino acids of the protein chain.

The role of protein synthesis is difficult to overestimate, since synthesized compounds perform very important functions. Almost all cellular structures consist of them.

So, we have described in general terms the process of protein biosynthesis and its biological role. This concludes our acquaintance with proteins. We hope you had a desire to continue it.