Proteins, the biological role of which will be considered today, are macromolecular compounds built from amino acids. Among all other organic compounds, they are among the most complex in their structure. According to the elemental composition, proteins differ from fats and carbohydrates: in addition to oxygen, hydrogen and carbon, they also contain nitrogen. In addition, sulfur is an indispensable component of the most important proteins, and some contain iodine, iron and phosphorus.
The biological role of protein is very high. It is these compounds that make up the bulk of the mass of protoplasm, as well as the nuclei of living cells. Proteins are found in all animal and plant organisms.
One or more functions
The biological role and functions of their various compounds are different. As a substance with a specific chemical structure, each protein performs a highly specialized function. Only in some cases it can perform several interconnected ones at once. For example, adrenaline, which is produced in the medullaadrenal glands, entering the bloodstream, increases blood pressure and oxygen consumption, blood sugar. In addition, it is a stimulant of metabolism, and in cold-blooded animals it is also a mediator of the nervous system. As you can see, it performs many functions at once.
Enzymatic (catalytic) function
Diverse biochemical reactions occurring in living organisms are carried out in mild conditions, in which the temperature is close to 40°C, and the pH values are almost 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 for the photolysis of water, are catalyzed in living organisms by enzymes. These elements are either proteins or complexes of proteins with a cofactor (organic molecule or metal ion). Enzymes act very selectively, starting the necessary process. So, the catalytic function discussed above is one of those that proteins perform. The biological role of these compounds, however, is not limited to its implementation. There are many more features that we'll look at below.
Transport function
For the existence of a cell, it is necessary that many substances enter into it, which provide it with energy and building material. All biological membranes are built in a commonprinciple. 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 the membranes, and hydrophobic "tails" are concentrated in their thickness. This structure remains impermeable to important components: amino acids, sugars, alkali metal ions. The penetration of these elements into the cell occurs with the help of transport proteins that are embedded in the cell membrane. Bacteria, for example, have a special protein that transports lactose (milk sugar) across the outer membrane.
Multicellular organisms have a system for transporting various substances from one organ to another. We are talking primarily about hemoglobin (pictured above). In addition, serum albumin (transport protein) is constantly present in the blood plasma. It has the ability to form strong complexes with fatty acids formed during the digestion of fats, as well as with a number of hydrophobic amino acids (for example, with tryptophan) and with many drugs (some penicillins, sulfonamides, aspirin). Transferrin, which mediates the transport of iron ions in the body, is another example. We can also mention ceruplasmin, which carries copper ions. So, we have considered the transport function that proteins perform. Their biological role is also very significant from this point of view.
Receptor function
Receptor proteins are of great importance, especially for the life support of multicellular organisms. They're built ininto the plasma cell 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 the most studied. They are located in a number of interneuronal contacts on the cell membrane, including at neuromuscular junctions, in the cerebral cortex. These proteins interact with acetylcholine and transmit a signal into the cell.
The neurotransmitter to receive the signal and convert it must be removed so that the cell has the opportunity 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. Isn't it true that the receptor function that proteins perform is also very important? The biological role of the next, protective function for the body is enormous. One simply cannot disagree with this.
Protection function
In the body, the immune system responds to the appearance of foreign particles in it by producing 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 special proteins. These proteins are released into the circulatory system. They recognize foreign particles, while forming a highly specific complex at the destruction stage. These proteins are called immunoglobulins. Foreign substances are called antigens.that trigger an immune system response.
Structural function
Besides 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 the tissues of living organisms. These proteins include, first of all, collagen. Collagen (pictured below) in mammals makes up about a quarter of the mass of proteins. It is synthesized in the main cells that make up connective tissue (called fibroblasts).
Initially, collagen is formed as procollagen - its precursor, undergoing chemical processing in fibroblasts. Then it is formed in the form of three polypeptide chains twisted into a spiral. They combine already outside the fibroblasts into collagen fibrils several hundred nanometers in diameter. The latter form collagen filaments, which can already be seen under a microscope. In elastic tissues (walls of the lungs, blood vessels, skin), the extracellular matrix, in addition to collagen, also contains the protein elastin. It can stretch over a fairly wide range and then return to its original state. Another example of a structural protein that can be given here is silk fibroin. It is isolated during the formation of the pupa of the silkworm caterpillar. It is the main component of silk threads. Let's move on to the description of motor proteins.
Motor proteins
And in the implementation of motor processes, the biological role of proteins is great. Let's briefly talk about this function. Muscle contraction is the process during which chemical energy is converted into mechanical work. Its direct participants are two proteins - myosin and actin. Myosin has a very unusual structure. It is formed from two globular heads and a tail (a long filamentous part). About 1600 nm is the length of one molecule. The heads account for approximately 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 again after ATP hydrolysis occurs 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 fact that a high molecular weight complex is formed in the absence of ATP. When it is added, the viscosity decreases sharply due to the destruction of the created complex, after which it gradually begins to recover as a result of ATP hydrolysis. In the process of muscle contraction, these interactions play a very important role.
Antibiotics
We continue to reveal the topic "The biological role of protein in the body." A very large and very important groupnatural compounds make up substances called antibiotics. They are of microbial origin. These substances are secreted by special types of microorganisms. The biological role of amino acids and proteins is indisputable, but 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 revolutionized the treatment of infectious diseases caused by bacteria. It should be noted that in most cases antibiotics do not act on viruses, so their use as antiviral drugs is ineffective.
Examples of antibiotics
The penicillin group was the first to be put into practice. Examples of this group are ampicillin and benzylpenicillin. Antibiotics are diverse in their mechanism of action and chemical nature. 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, they are destructive for bacterial cells, and slightly toxic for animals and humans. These antibiotics include streptomycin and levomycetin (chloramphenicol).
The biological role of protein biosynthesis is very important, and this process itself has several stages. We will only talk about it in general terms.
The process and biological role of protein biosynthesis
This process is multi-step and very complex. It occurs in ribosomes -special organelles. The cell contains many ribosomes. E. coli, for example, has about 20 thousand of them.
"Describe the process of protein biosynthesis and its biological role" - such a task many of us received in school. And for many it has been difficult. Well, let's try to figure it out together.
Protein molecules are polypeptide chains. They consist, as you already know, of individual amino acids. However, the latter are not active enough. In order to combine and form a protein molecule, they require activation. It occurs as a result of the action of special enzymes. Each amino acid has its own enzyme specifically tuned to it. The energy source for this process is ATP (adenosine triphosphate). As a result of activation, the amino acid becomes more labile and binds under the action of this enzyme to t-RNA, which transfers it to the ribosome (because of this, this RNA is called transport). Thus, activated amino acids connected with tRNA enter the ribosome. The ribosome is a kind of conveyor for assembling protein chains from incoming amino acids.
The role of protein synthesis is difficult to overestimate, since the synthesized compounds perform very important functions. Almost all cellular structures are made up of them.
So, we have described in general terms the process of protein biosynthesis and its biological role. This concludes our introduction to proteins. We hope you have the desire to continue it.
