Proteins, the biological role of which will be considered today, are high-molecular compounds built from amino acids. Among all other organic compounds, they are one of the most complex in their structure. In terms of 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 large. 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 certain chemical structure, each protein performs a highly specialized function. Only in some cases can he perform several interrelated at once. For example, adrenaline, which is produced in the adrenal medulla, enters the bloodstream, increases blood pressure and oxygen consumption, and blood sugar. In addition, it is a stimulant of metabolism, and in cold-blooded animals - 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, 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 (an organic molecule or metal ion). Enzymes act very selectively, starting the necessary process. So, the catalytic function discussed above is one of those that carry proteins. The biological role of these compounds, however, is not limited to its implementation. There are many other features that we will cover below.
Transport function
For a cell to exist, it is necessary that many substances enter the cell, which provide it with energy and building material. All biological membranes are built on a general principle. This is a double layer of lipids, proteins are immersed in it. At the same time, hydrophilic sections of macromolecules are concentrated on the membrane surface, and hydrophobic "tails" in their thickness. This structure remains impervious to important components: amino acids, sugars, alkali metal ions. The penetration of these elements into the cell occurs with the help of transport proteins, which are embedded in the cell membrane. Bacteria, for example, have a special protein that allows 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 addition, serum albumin (transport protein) is constantly 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, tryptophan) and with many medications (some penicillins, sulfanilamides, aspirin). Transferrin, which provides the transfer of iron ions in the body, is another example. Ceruplasmin, which carries copper ions, can also be mentioned. So, we examined the transport function that proteins perform. Their biological role from this point of view is very significant.
Receptor function
Receptor proteins are of great importance, especially for ensuring the vital activity of multicellular organisms. They are built into the plasma cell membrane and serve to perceive and further transform the signals that enter the cell. In this case, the signals can be from other cells, as well as from the environment. Acetylcholine receptors are currently the most studied. They are located in a number of interneuronal contacts on the cell membrane, including in neuromuscular connections, in the cerebral cortex. These proteins interact with acetylcholine and transmit a signal into the cell.
The neurotransmitter for receiving the signal and its conversion must be removed 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 is a catalyst for the hydrolysis of acetylcholine to choline and acetate. Isn’t the receptor function that proteins perform is very important? The biological role of the following protective function is enormous for the body. One simply cannot but agree with this.
Protective function
In the body, the immune system responds to the appearance of foreign particles in it by the production of a large number of lymphocytes. They are capable of damaging 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 secreted into the circulatory system. They recognize foreign particles, while forming a highly specific complex at the stage of destruction. These proteins are called immunoglobulins. And antigens are called foreign substances that cause the response of the immune system.
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. Such proteins include, first of all, collagen. Collagen (see photo below) in mammals makes up about a quarter of the mass of proteins. It is synthesized in the main cells that make up the connective tissue (they are called fibroblasts).
Initially, collagen is formed as collagen, its precursor chemically processed in fibroblasts. Then it is formed in the form of three polypeptide chains twisted into a spiral. They unite already outside of fibroblasts into collagen fibrils of several hundred nanometers in diameter. The latter form collagen threads, which can already be seen under the microscope. In elastic tissues (walls of the lungs, blood vessels, and skin), the extracellular matrix, in addition to collagen, also contains 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 secreted during the formation of the pupae of the silkworm caterpillar. This is the main component of silk threads. We turn to the description of motor proteins.
Motor proteins
And in the implementation of motor processes, the biological role of proteins is great. Briefly tell about their 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 of two globular heads and a tail (a long threadlike part). About 1600 nm is the length of one molecule. At the same time, 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 formation of a high molecular weight complex in the absence of ATP. When it is added, the viscosity sharply decreases 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 large role.
Antibiotics
We continue to expand on the topic "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 secreted by special types of microorganisms. The biological role of amino acids and proteins is undeniable, but antibiotics have a special, very important function. They inhibit the growth of microorganisms competing 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 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 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 almost do not interact with eukaryotic ribosomes. Therefore, they are fatal to bacterial cells, and are not toxic to animals and humans. These antibiotics include streptomycin and chloramphenicol.
The biological role of protein biosynthesis is very important, and this 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 multi-stage and very complex. It occurs in ribosomes - special organelles. There are many ribosomes in the cell. E. coli, for example, have about 20 thousand.
“Describe the process of protein biosynthesis and its biological role" - many of us received this task at school. And for many it caused difficulties. 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 connect and form a protein molecule, they require activation. It occurs as a result of the action of special enzymes. Each amino acid at the same time has its own enzyme, specifically tuned specifically for it. The energy source 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). Thus, activated amino acids connected to t-RNA enter the ribosome. Ribosome is a kind of conveyor for assembling a protein chain 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 composed 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 have a desire to continue it.