The structure of protein molecules. Relationship of properties, functions and activity of proteins with their structural organization (specificity, species affiliation, recognition effect, dynamism, effect of cooperative interaction).

Squirrels - These are high-molecular nitrogen-containing substances, consisting of amino acid residues linked by peptide bonds. Proteins are otherwise called proteins;

Simple proteins are built from amino acids and, upon hydrolysis, break down, respectively, only into amino acids. Complex proteins are two-component proteins that consist of some simple protein and a non-protein component called a prosthetic group. During the hydrolysis of complex proteins, in addition to free amino acids, the non-protein part or its decay products are released. Simple proteins, in turn, are divided on the basis of some conditionally selected criteria into a number of subgroups: protamines, histones, albumins, globulins, prolamins, glutelins, etc.

The classification of complex proteins is based on the chemical nature of their non-protein component. In accordance with this, there are: phosphoproteins (contain phosphoric acid), chromoproteins (they include pigments), nucleoproteins (contain nucleic acids), glycoproteins (contain carbohydrates), lipoproteins (contain lipids) and metalloproteins (contain metals).

3. Protein structure.

The sequence of amino acid residues in the polypeptide chain of a protein molecule is called protein primary structure. The primary structure of a protein, in addition to a large number of peptide bonds, usually also contains a small number of disulfide (-S-S-) bonds. The spatial configuration of the polypeptide chain, more precisely the type polypeptide helix, determinessecondary protein structure, it is presented in mostly α-helix, which is fixed by hydrogen bonds. tertiary structure-polypeptide chain, wholly or partially coiled, is located or packaged in space (in a globule). The known stability of the protein tertiary structure is provided by hydrogen bonds, intermolecular van der Waals forces, electrostatic interaction of charged groups, etc.

Quaternary protein structure - a structure consisting of a certain number of polypeptide chains occupying a strictly fixed position relative to each other.

The classic example of a protein having a quaternary structure is hemoglobin.

Physical properties of proteins: high viscosity solutions,

negligible diffusion, large swelling capacity, optical activity, mobility in an electric field, low osmotic pressure and high oncotic pressure, ability to absorb UV rays at 280 nm, like amino acids, are amphoteric due to the presence of free NH2- and COOH-groups and are characterized, respectively, by all St. you acids and bases. They have pronounced hydrophilic properties. Their solutions have a very low osmotic pressure, high viscosity and little diffusivity. Proteins are capable of swelling to a very large extent. The phenomenon of light scattering, which underlies the quantitative determination of proteins by nephelometry, is associated with the colloidal state of proteins.

Proteins are able to adsorb low molecular weight organic compounds and inorganic ions on their surface. This property determines the transport functions of individual proteins.

Chemical properties of proteins are diverse, since the side radicals of amino acid residues contain various functional groups (-NH2, -COOH, -OH, -SH, etc.). A characteristic reaction for proteins is the hydrolysis of peptide bonds. Due to the presence of both amino and carboxyl groups, proteins have amphoteric properties.

Protein denaturation- destruction of bonds that stabilize the quaternary, tertiary and secondary structures, leading to disorientation of the configuration of the protein molecule and accompanied by the loss of native properties.

There are physical (temperature, pressure, mechanical impact, ultrasonic and ionizing radiation) and chemical (heavy metals, acids, alkalis, organic solvents, alkaloids) factors that cause denaturation.

The reverse process is renaturation, that is, the restoration of the physicochemical and biological properties of the protein. Renaturation is not possible if the primary structure is affected.

Most proteins denature when heated with a solution above 50-60 ° C. External manifestations of denaturation are reduced to a loss of solubility, especially at the isoelectric point, an increase in the viscosity of protein solutions, an increase in the amount of free functional SH-rpypp and a change in the nature of X-ray scattering, globules of native protein molecules and form random and disordered structures.

contraction function. actin and myosin are specific proteins of muscle tissue. structural function. fibrillar proteins, in particular collagen in connective tissue, keratin in hair, nails, skin, elastin in the vascular wall, etc.

hormonal function. A number of hormones are represented by proteins or polypeptides, such as hormones of the pituitary gland, pancreas, etc. Some hormones are derivatives of amino acids.

Nutritional (reserve) function. reserve proteins that are sources of nutrition for the fetus. The main protein of milk (casein) also performs a mainly nutritional function.

Biological functions of proteins. Diversity of proteins in terms of structural organization and biological function. Polymorphism. Differences in the protein composition of organs and tissues. Changes in the composition in ontogeny and in diseases.

-Degree of difficulty Protein structures are divided into simple and complex. Simple or one-component proteins consist only of the protein part and, when hydrolyzed, give amino acids. To difficult or two-component include proteins, in the composition of which includes a protein and an additional group of non-protein nature, called prosthetic. ( lipids, carbohydrates, nucleic acids can act); respectively, complex proteins are called lipoproteins, glycoproteins, nucleoproteins.

- according to the shape of the protein molecule proteins are divided into two groups: fibrillar (fibrous) and globular (corpuscular). fibrillar proteins characterized by a high ratio of their length to diameter (several tens of units). Their molecules are filamentous and are usually collected in bundles that form fibers. (they are the main components of the outer layer of the skin, forming the protective covers of the human body). They are also involved in the formation of connective tissue, including cartilage and tendons.

The vast majority of natural proteins are globular. For globular proteins characterized by a small ratio of length to diameter of the molecule (several units). Having a more complex conformation, globular proteins are also more diverse.

-In relation to conventionally selected solvents allocate albuminsandglobulins. Albumins dissolve very well in water and concentrated saline solutions. Globulins insoluble in water and in solutions of salts of moderate concentration.

--Functional classification of proteins the most satisfactory, since it is based not on a random sign, but on a performed function. In addition, it is possible to distinguish the similarity of structures, properties and functional activity of specific proteins included in any class.

catalytically active proteins called enzymes. They catalyze almost all chemical transformations in the cell. This group of proteins will be discussed in detail in Chapter 4.

Hormones regulate metabolism within cells and integrate metabolism in various cells of the body as a whole.

Receptors selectively bind various regulators (hormones, mediators) on the surface of cell membranes.

Transport proteins carry out the binding and transport of substances between tissues and through cell membranes.

Structural proteins . First of all, this group includes proteins involved in the construction of various biological membranes.

Squirrels - inhibitors enzymes constitute a large group of endogenous inhibitors. They regulate the activity of enzymes.

Contractile squirrels provide a mechanical reduction process using chemical energy.

Toxic proteins - some proteins and peptides secreted by organisms (snakes, bees, microorganisms) that are poisonous to other living organisms.

protective proteins. antibodies - substances of a protein nature produced by an animal organism in response to the introduction of an antigen. Antibodies, interacting with antigens, deactivate them and thereby protect the body from the effects of foreign compounds, viruses, bacteria, etc.

The protein composition depends on the physiology. Activity, food composition and diet, biorhythms. In the process of development, the composition changes significantly (from the zygote to the formation of differentiated organs with specialized functions). For example, erythrocytes contain hemoglobin, which provides oxygen transport by blood, mice cells contain contractile proteins actin and myosin, rhodopsin is a protein in the retina, etc. In diseases, the protein composition changes - proteinopathy. Hereditary proteinopathies develop as a result of damage to the genetic apparatus. Any protein is not synthesized at all or is synthesized, but its primary structure is changed (sickle cell anemia). Any disease is accompanied by a change in the protein composition i.e. acquired proteinopathy develops. In this case, the primary structure of proteins is not disturbed, but a quantitative change in proteins occurs, especially in those organs and tissues in which the pathological process develops. For example, with pancreatitis, the production of enzymes necessary for the digestion of nutrients in the gastrointestinal tract decreases.

Factors of damage to the structure and function of proteins, the role of damage in the pathogenesis of diseases. Proteinopathy

The protein composition of the body of a healthy adult is relatively constant, although changes in the amount of individual proteins in organs and tissues are possible. In various diseases, there is a change in the protein composition of tissues. These changes are called proteinopathies. There are hereditary and acquired proteinopathies. Hereditary proteinopathies develop as a result of damage in the genetic apparatus of a given individual. Any protein is not synthesized at all or is synthesized, but its primary structure is changed. Any disease is accompanied by a change in the protein composition of the body, i.e. acquired proteinopathy develops. In this case, the primary structure of proteins is not disturbed, but usually there is a quantitative change in proteins, especially in those organs and tissues in which the pathological process develops. For example, with pancreatitis, the production of enzymes necessary for the digestion of nutrients in the gastrointestinal tract decreases.

In some cases, acquired proteinopathies develop as a result of changes in the conditions in which proteins function. So, when the pH of the medium changes to the alkaline side (alkaloses of various nature), the conformation of hemoglobin changes, its affinity for O 2 increases and the delivery of O 2 to tissues decreases (tissue hypoxia).

Sometimes, as a result of the disease, the level of metabolites in cells and blood serum increases, which leads to the modification of some proteins and disruption of their function.

In addition, proteins can be released from the cells of the damaged organ into the blood, which are normally determined there only in trace amounts. In various diseases, biochemical studies of the protein composition of the blood are often used to clarify the clinical diagnosis.

4. Primary structure of proteins. Dependence of the properties and functions of proteins on their primary structure. Changes in the primary structure, proteinopathy.

But life on our planet originated from a coacervate droplet. It was also a protein molecule. That is, the conclusion follows that it is these chemical compounds that are the basis of all life that exists today. But what are protein structures? What role do they play in the body and people's lives today? What types of proteins are there? Let's try to figure it out.

Proteins: a general concept

From the point of view, the molecule of the substance in question is a sequence of amino acids interconnected by peptide bonds.

Each amino acid has two functional groups:

• carboxyl -COOH;
• an amino group -NH 2 .

It is between them that the formation of bonds in different molecules occurs. Thus, the peptide bond has the form -CO-NH. A protein molecule may contain hundreds or thousands of such groups, it will depend on the specific substance. The types of proteins are very diverse. Among them there are those that contain essential amino acids for the body, which means they must be ingested with food. There are varieties that perform important functions in the cell membrane and its cytoplasm. Biological catalysts are also isolated - enzymes, which are also protein molecules. They are widely used in human life, and not only participate in the biochemical processes of living beings.

The molecular weight of the compounds under consideration can vary from several tens to millions. After all, the number of monomer units in a large polypeptide chain is unlimited and depends on the type of a particular substance. The protein in its pure form, in its native conformation, can be seen when examining a chicken egg in a light yellow, transparent, dense colloidal mass, inside which the yolk is located - this is the desired substance. The same can be said about fat-free cottage cheese. This product is also almost pure protein in its natural form.

However, not all compounds under consideration have the same spatial structure. In total, four organizations of the molecule are distinguished. Species determine its properties and speak of the complexity of the structure. It is also known that more spatially entangled molecules undergo extensive processing in humans and animals.

Types of protein structures

There are four of them in total. Let's take a look at what each of them is.

1. Primary. Represents the usual linear sequence of amino acids connected by peptide bonds. There are no spatial twists, no spiralization. The number of links included in the polypeptide can reach several thousand. Types of proteins with a similar structure are glycylalanine, insulin, histones, elastin, and others.
2. Secondary. It consists of two polypeptide chains that are twisted in the form of a spiral and oriented towards each other by formed turns. In this case, hydrogen bonds form between them, holding them together. This is how a single protein molecule is formed. The types of proteins of this type are as follows: lysozyme, pepsin and others.
3. Tertiary conformation. It is a densely packed and compactly coiled secondary structure. Here, other types of interaction appear, in addition to hydrogen bonds - this is the van der Waals interaction and the forces of electrostatic attraction, hydrophilic-hydrophobic contact. Examples of structures are albumin, fibroin, silk protein, and others.
4. Quaternary. The most complex structure, which is several polypeptide chains twisted into a spiral, rolled into a ball and united all together into a globule. Examples such as insulin, ferritin, hemoglobin, collagen illustrate just such a protein conformation.

If we consider all the given structures of molecules in detail from a chemical point of view, then the analysis will take a long time. Indeed, in fact, the higher the configuration, the more complex and intricate its structure, the more types of interactions are observed in the molecule.

Denaturation of protein molecules

One of the most important chemical properties of polypeptides is their ability to break down under the influence of certain conditions or chemical agents. For example, various types of protein denaturation are widespread. What is this process? It consists in the destruction of the native structure of the protein. That is, if initially the molecule had a tertiary structure, then after the action of special agents it will collapse. However, the sequence of amino acid residues remains unchanged in the molecule. Denatured proteins quickly lose their physical and chemical properties.

What reagents can lead to the process of conformation destruction? There are several.

1. Temperature. When heated, there is a gradual destruction of the quaternary, tertiary, secondary structure of the molecule. Visually, this can be observed, for example, when frying an ordinary chicken egg. The resulting "protein" is the primary structure of the albumin polypeptide that was in the raw product.
2. Radiation.
3. Action by strong chemical agents: acids, alkalis, salts of heavy metals, solvents (for example, alcohols, ethers, benzene and others).

This process is sometimes also called the melting of the molecule. The types of protein denaturation depend on the agent under whose action it occurred. Moreover, in some cases, the reverse process takes place. This is renaturation. Not all proteins are able to restore their structure back, but a significant part of them can do this. So, chemists from Australia and America carried out the renaturation of a boiled chicken egg using some reagents and a centrifugation method.

This process is important for living organisms in the synthesis of polypeptide chains by ribosomes and rRNA in cells.

Hydrolysis of a protein molecule

Along with denaturation, proteins are characterized by another chemical property - hydrolysis. This is also the destruction of the native conformation, but not to the primary structure, but completely to individual amino acids. An important part of digestion is protein hydrolysis. The types of hydrolysis of polypeptides are as follows.

1. Chemical. Based on the action of acids or alkalis.
2. Biological or enzymatic.

However, the essence of the process remains unchanged and does not depend on what types of protein hydrolysis take place. As a result, amino acids are formed, which are transported to all cells, organs and tissues. Their further transformation consists in the participation of the synthesis of new polypeptides, already those that are necessary for a particular organism.

In industry, the process of hydrolysis of protein molecules is used just to obtain the desired amino acids.

Functions of proteins in the body

Various types of proteins, carbohydrates, fats are vital components for the normal functioning of any cell. And that means the whole organism as a whole. Therefore, their role is largely due to the high degree of significance and ubiquity within living beings. There are several main functions of polypeptide molecules.

1. catalytic. It is carried out by enzymes that have a protein structure. We'll talk about them later.
2. Structural. The types of proteins and their functions in the body primarily affect the structure of the cell itself, its shape. In addition, polypeptides that perform this role form hair, nails, mollusc shells, and bird feathers. They are also a certain armature in the body of the cell. Cartilage is also made up of these types of proteins. Examples: tubulin, keratin, actin and others.
3. Regulatory. This function is manifested in the participation of polypeptides in such processes as: transcription, translation, cell cycle, splicing, mRNA reading, and others. In all of them, they play an important role as a regulator.
4. Signal. This function is performed by proteins located on the cell membrane. They transmit different signals from one unit to another, and this leads to communication between tissues. Examples: cytokines, insulin, growth factors and others.
5. Transport. Some types of proteins and their functions that they perform are simply vital. This happens, for example, with the protein hemoglobin. It transports oxygen from cell to cell in the blood. For a person it is irreplaceable.
6. Spare or reserve. Such polypeptides accumulate in plants and animal eggs as a source of additional nutrition and energy. An example is globulins.
7. Motor. A very important function, especially for the simplest organisms and bacteria. After all, they are able to move only with the help of flagella or cilia. And these organelles, by their nature, are nothing more than proteins. Examples of such polypeptides are the following: myosin, actin, kinesin and others.

Obviously, the functions of proteins in the human body and other living beings are very numerous and important. This once again confirms that without the compounds we are considering, life on our planet is impossible.

Protective function of proteins

Polypeptides can protect against various influences: chemical, physical, biological. For example, if the body is in danger in the form of a virus or bacteria of an alien nature, then immunoglobulins (antibodies) enter into battle with them, performing a protective role.

If we talk about physical effects, then fibrin and fibrinogen, which are involved in blood coagulation, play an important role here.

Food proteins

The types of dietary protein are as follows:

• complete - those that contain all the amino acids necessary for the body;
• incomplete - those in which there is an incomplete amino acid composition.

However, both are important for the human body. Especially the first group. Each person, especially during periods of intensive development (childhood and adolescence) and puberty, must maintain a constant level of proteins in himself. After all, we have already considered the functions that these amazing molecules perform, and we know that practically not a single process, not a single biochemical reaction within us can do without the participation of polypeptides.

That is why it is necessary to consume every day the daily norm of proteins that are contained in the following products:

• egg;
• milk;
• cottage cheese;
• meat and fish;
• beans;
• beans;
• peanut;
• wheat;
• oats;
• lentils and others.

If one consumes 0.6 g of the polypeptide per kg of weight per day, then a person will never lack these compounds. If for a long time the body does not receive the necessary proteins, then a disease occurs, which has the name of amino acid starvation. This leads to severe metabolic disorders and, as a result, many other ailments.

Proteins in a cell

Inside the smallest structural unit of all living things - cells - there are also proteins. Moreover, they perform almost all of the above functions there. First of all, the cytoskeleton of the cell is formed, consisting of microtubules, microfilaments. It serves to maintain shape, as well as for internal transport between organelles. Various ions and compounds move along protein molecules, as along channels or rails.

The role of proteins immersed in the membrane and located on its surface is also important. Here they perform both receptor and signal functions, take part in the construction of the membrane itself. They stand guard, which means they play a protective role. What types of proteins in the cell can be attributed to this group? There are many examples, here are a few.

1. actin and myosin.
2. Elastin.
3. Keratin.
4. Collagen.
5. Tubulin.
6. Hemoglobin.
7. Insulin.
8. Transcobalamin.
9. Transferrin.
10. Albumen.

In total, there are several hundred different ones that constantly move inside each cell.

Types of proteins in the body

Of course, they have a huge variety. If you try to somehow divide all existing proteins into groups, then you can get something like this classification.

In general, many features can be taken as a basis for classifying proteins found in the body. One does not yet exist.

Enzymes

Biological catalysts of protein nature, which significantly accelerate all ongoing biochemical processes. Normal exchange is impossible without these compounds. All processes of synthesis and decay, assembly of molecules and their replication, translation and transcription, and others are carried out under the influence of a specific type of enzyme. Examples of these molecules are:

• oxidoreductases;
• transferases;
• catalase;
• hydrolases;
• isomerases;
• lyases and others.

Today, enzymes are used in everyday life. So, in the production of washing powders, so-called enzymes are often used - these are biological catalysts. They improve the quality of washing while observing the specified temperature regime. Easily binds to dirt particles and removes them from the surface of fabrics.

However, due to their protein nature, enzymes do not tolerate too hot water or the proximity to alkaline or acidic drugs. Indeed, in this case, the process of denaturation will occur.

Structural function of proteins

Structural function of proteins is that proteins

• participate in the formation of almost all cell organelles, largely determining their structure (shape);
• form a cytoskeleton that gives shape to cells and many organelles and provides the mechanical shape of a number of tissues;
• are part of the intercellular substance, which largely determines the structure of tissues and the shape of the body of animals.

Proteins of the intercellular substance

In the human body, there are more proteins of the intercellular substance than all other proteins. The main structural proteins of the intercellular substance are fibrillar proteins.

collagens

Collagens are a family of proteins, in the human body they make up to 25 - 30% of the total mass of all proteins. In addition to the structural function, collagen also performs mechanical, protective, nutritional and reparative functions.

The collagen molecule is a right-handed helix of three α-chains.

In total, a person has 28 types of collagen. All of them are similar in structure.

Elastin

Elastin is widely distributed in connective tissue, especially in the skin, lungs, and blood vessels. Common characteristics for elastin and collagen are the high content of glycine and proline. Elastin contains much more valine and alanine and less glutamic acid and arginine than collagen. Elastin contains desmosine and isodesmosine. these compounds can only be found in elastin. Elastin is insoluble in aqueous solutions (like collagen), in solutions of salts, acids and alkalis, even when heated. Elastin contains a large number of amino acid residues with non-polar side groups, which, apparently, determines the high elasticity of its fibers.

Other extracellular matrix proteins

Keratins are divided into two groups: α-keratins and β-keratins. The strength of keratin is second only to chitin. A characteristic feature of keratins is their complete insolubility in water at pH 7.0. They contain the residues of all amino acids in the molecule. They differ from other fibrillar structural proteins (for example, collagen) primarily by their increased content of cysteine ​​residues. The primary structure of the polypeptide chains of a-keratins has no periodicity.

Other intermediate filament proteins

In other types of tissues (except epithelium), intermediate filaments are formed by proteins similar in structure to keratin - vimentin, neurofilament proteins, etc. Lamin proteins in most eukaryotic cells form the inner lining of the nuclear envelope. The nuclear lamina, which consists of them, supports the nuclear membrane and is in contact with chromatin and nuclear RNA.

Tubulin

Structural proteins of organelles

Proteins create and determine the shape (structure) of many cell organelles. Organelles such as ribosomes, proteasomes, nuclear pores, etc. are mainly composed of proteins. Histones are necessary for the assembly and packaging of DNA strands into chromosomes. The cell walls of some protists (for example, chlamydomonas) are composed of proteins; in the composition of the cell membrane of many bacteria and archaea there is a protein layer (S-layer), which is attached to the cell wall in gram-positive species, and to the outer membrane in gram-negative species. Prokaryotic flagella are made up of flagellin protein.

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The functioning of the human body became clear at the beginning of the 19th century. Scientists designated these substances with the Greek term "proteins", from the word protos - "main, first".

The main feature of these chemical compounds is that they are the basis that the body uses to create new cells. Their other functions are to provide regulatory and metabolic processes; in the performance of transport functions (for example, hemoglobin protein, which distributes oxygen throughout the body with blood flow); in the formation of muscle fibers; in the management of many vital functions of the body (a striking example is the protein insulin); in regulating the process of digestion, energy metabolism; in protecting the body.

The chemical structure of these substances is determined by the number of amino acids that make up the protein molecules. The molecules are quite large in size. These substances are high-molecular organic substances and are a chain of amino acids linked by a peptide bond. The amino acid composition of proteins is determined by the genetic code. Many variations in the combination of amino acids gives a variety of properties of protein molecules. As a rule, they are interconnected and form complex complexes.

The classification of proteins has not been finalized, since not all proteins have been studied by scientists. The role of many of them continues to be a mystery to people. So far, proteins are divided according to their biological role and according to which amino acids are included in their composition. For our nutrition, it is not the protein itself that is valuable, but the amino acids that make it up. Amino acids are one of the varieties of organic acids. There are more than 100 of them. Without them, metabolic processes are impossible.

The body cannot fully absorb the proteins that come from food. Most of them are destroyed by acidic digestive juices. Proteins are broken down into amino acids. The body “takes” after the breakdown the amino acids it needs and constructs the necessary proteins from them. In this case, the transformation of one amino acid into another can occur. In addition to transformation, they can also be independently synthesized in the body.

However, not all amino acids can be produced by our body. Those that are not synthesized are called irreplaceable, because the body needs them, and can only get them from the outside. Essential amino acids cannot be replaced by others. These include methionine, lysine, isoleucine, leucine, phenylalanine, threonine, valine. In addition, there are other amino acids that are formed exclusively from the essential phenylalanine and methionine. Therefore, the quality of nutrition is determined not by the amount of incoming proteins, but by their qualitative composition. For example, potatoes, white cabbage, beets, cabbage, legumes, bread contain a large amount of tryptophan, lysine, methionine.

The course of protein metabolism in our body depends on a sufficient amount of the necessary proteins. The splitting and transformation of some substances into others occurs with the release of the energy needed by the body.

As a result of the vital activity of the body, there is a constant loss of part of the proteins. Approximately 30 g per day is lost from protein substances coming from outside. Therefore, taking into account the loss, the diet should contain a sufficient amount of these substances to ensure the health of the body.

The consumption of protein substances by the body depends on various factors: performing difficult physical work or being at rest; emotional condition. Per day, the rate of protein intake is a total of at least 50 grams for adults (this is approximately 0.8 grams per kilogram of body weight). Children, due to intensive growth and development, require more proteins - up to 1.9 grams per kilogram of body weight.

However, even a large amount of protein substances eaten does not guarantee a balanced amount of amino acids in them. Therefore, the diet should be varied so that the body can get the most out of it in the form of different amino acids. We are not talking about the fact that if today there was no tryptophan in the food you ate, then tomorrow you will get sick. No, the body "knows how" to store useful amino acids in small quantities and use them if necessary. However, the cumulative capacity of the body is not too high, so the reserves of useful substances must be regularly replenished.

If, due to personal beliefs (vegetarianism) or for health reasons (problems with the gastrointestinal tract and dietary nutrition), you have a dietary restriction, then you need to consult a dietitian to adjust your diet and restore the balance of proteins in the body.
During intensive sports activities, the body needs a large amount of proteins. Specially for such people, sports nutrition is produced. However, the intake of proteins should correspond to the physical activity performed. An excess of these substances, contrary to popular belief, will not lead to a sharp increase in muscle mass.

The variety of functions of proteins covers almost all biochemical processes occurring in the body. They can be called biochemical catalysts.
Proteins form the cytoskeleton, which maintains the shape of cells. Without proteins, the successful functioning of the immune system is impossible.

An excellent food source of proteins are meat, milk, fish, grains, legumes, nuts. Fruits, berries and vegetables are less rich in proteins.

The first protein that has been studied to determine its amino acid sequence is insulin. For this achievement, F. Sanger received the Nobel Prize in the 60s of the last century. And scientists D. Kendrew and M. Perutz at the same time were able to create a three-dimensional structure of myoglobin and hemoglobin using the X-ray diffraction technique. They were also awarded the Nobel Prize for this.

History of study

The founder of the study of proteins is Antoine Francois de Fourcroix. He singled them out in a separate class after he noticed their property to denature (or fold) under the influence of acids or high temperature. He investigated fibrin (isolated from blood), gluten (isolated from wheat grain) and albumin (egg white).


The Dutch scientist G. Mulder supplemented the scientific work of his French colleague de Fourcroix and analyzed the protein composition. Based on this analysis, he hypothesized that most protein molecules have a similar empirical formula. He was also the first to be able to determine the molecular weight of a protein.
According to Mulder, any protein consists of small structural components - "proteins". And in 1838, the Swedish scientist J. Berzelius proposed the term "proteins" as a common name for all proteins.

In the next 30-40 years, studies were carried out on most of the amino acids that make up proteins. In 1894, A. Kossel, a German physiologist, made the assumption that it is amino acids that are the very structural components of proteins, and that they are interconnected by peptide bonds. He tried to study the amino acid sequence of the protein.
In 1926, the dominant role of proteins in the body was finally recognized. This happened when the US chemist D. Sumner proved that urease (an enzyme without which many chemical processes are impossible) is a protein.

It was extremely difficult at that time to isolate pure proteins for the needs of science. That is why the first experiments were carried out using those polypeptides that could be purified in significant quantities at minimal cost - these are blood proteins, chicken proteins, various toxins, enzymes of digestive or metabolic origin, released after slaughtering cattle. In the late 1950s, it was possible to purify bovine pancreatic ribonuclease. It is this substance that has become an experimental object for many scientists.

In modern science, the study of proteins has continued at a qualitatively new level. There is a branch of biochemistry called proteomics. Now, thanks to proteomics, it is possible to study not only isolated purified proteins, but also a parallel, simultaneous change in the modification of many proteins belonging to different cells and tissues. Scientists can now theoretically calculate the structure of a protein from its amino acid sequence. Cryoelectron microscopy methods make it possible to study large and small protein complexes.

Protein properties

The size of proteins can be measured in terms of the number of amino acids that make them up, or in daltons, which denotes their molecular weight. For example, yeast proteins are composed of 450 amino acids and have a molecular weight of 53 kilodaltons. The largest protein known to modern science, which is called titin, consists of more than 38 thousand amino acids and has a molecular weight of about 3700 kilodaltons.
Proteins that bind to nucleic acids by interacting with their phosphate residues are considered basic proteins. These include protamines and histones.

Proteins are distinguished by their degree of solubility, most of them are highly soluble in water. However, there are also exceptions. Fibroin (the basis of cobwebs and silk) and keratin (the basis of human hair, as well as wool in animals and feathers in birds), are insoluble.

Denaturation

As a rule, proteins retain the physicochemical properties and structure of the living organism to which they belong. Consequently, if the body is adapted to a certain temperature, then the protein will withstand it and not change its properties.
Changes in conditions such as ambient temperature, or exposure to an acid/alkaline environment cause the protein to lose its secondary, tertiary, and quaternary structures. The loss of the native structure inherent in a living cell is called protein denaturation or folding. Denaturation may be partial or complete, irreversible or reversible. The most popular and everyday example of irreversible denaturation is the hard boiled egg. Under the influence of high temperature, ovalbumin, a transparent protein, becomes opaque and dense.

In some cases, denaturation is reversible; the reverse state of the protein can be restored using ammonium salts. Reversible denaturation is used as a protein purification method.

Simple and complex proteins

In addition to peptide chains, some proteins also contain non-amino acid structural units. According to the criterion of the presence or absence of non-amino acid fragments, proteins are divided into two groups: complex and simple proteins. Simple proteins are made up of only amino acid chains. Complex proteins contain fragments that are non-protein in nature.

According to the chemical nature of complex proteins, five classes are distinguished:

• Glycoproteins.
• Chromoproteins.
• Phosphoproteins.
• Metalloproteins.
• Lipoproteins.

Glycoproteins contain covalently linked carbohydrate residues and their variety - proteoglycans. Glycoproteins include, for example, immunoglobulins.

Chromoproteins is the general name for complex proteins, which include flavoproteins, chlorophylls, hemoglobin, and others.

Proteins called phosphoproteins contain residues of phosphoric acid. This group of proteins includes, for example, milk casein.

Metalloproteins are proteins that contain covalently bound ions of certain metals. Among them there are proteins that perform transport and storage functions (transferrin, ferritin).

Complex lipoprotein proteins contain lipid residues in their composition. Their function is the transport of lipids.

Biosynthesis of proteins

Living organisms create proteins from amino acids based on genetic information that is encoded in genes. Each of the synthesized proteins consists of a completely unique sequence of connected amino acids. A unique sequence is determined by such a factor as the nucleotide sequence of a gene that encodes information about a given protein.

The genetic code is made up of codons. A codon is a unit of genetic information consisting of nucleotide residues. Each codon is responsible for attaching one amino acid to a protein. Their total number is 64. Some amino acids are determined not by one, but by several codons.

Functions of proteins in the body

Along with other biological macromolecules (polysaccharides and lipids), proteins are needed by the body to carry out most of the life processes in cells. Proteins carry out metabolic processes and energy transformations. They are part of organelles - cellular structures, participate in the synthesis of intercellular substance.

It should be noted that the classification of proteins according to their functions is rather arbitrary, because in some living organisms the same protein can perform several different functions. Proteins perform many functions due to the fact that they have high enzymatic activity. In particular, these enzymes include the motor protein myosin, as well as the regulatory proteins of protein kinase.

catalytic function

The most studied role of proteins in the body is the catalysis of various chemical reactions. Enzymes are a group of proteins with specific catalytic properties. Each of these enzymes is a catalyst for one or more similar reactions. Science knows several thousand enzymatic substances. For example, the substance pepsin, which breaks down proteins during digestion, is an enzyme.

More than 4,000 reactions in our body need to be catalyzed. Without the action of enzymes, the reaction proceeds tens and hundreds of times slower.
Molecules that attach to an enzyme during a reaction and then change are called substrates. The enzyme contains many amino acids, but not all of them interact with the substrate, and even more so, not all of them directly participate in the catalytic process. The part of the enzyme to which the substrate is attached is considered the active site of the enzyme.

structural function

Structural proteins of the cytoskeleton are a kind of rigid framework that gives shape to cells. Thanks to them, the shape of the cells can change. These include elastin, collagen, keratin. The main components of the intercellular substance in the connective tissue are collagen and elastin. Keratin is the basis for the formation of hair and nails, as well as feathers in birds.

Protective function

There are several protective functions of proteins: physical, immune, chemical.
Collagen is involved in the formation of physical protection. It forms the basis of the intercellular substance of such types of connective tissue as bones, cartilage, tendons and deep layers of the skin (dermis). Examples of this group of proteins are thrombins and fibrinogens, which are involved in blood coagulation.

Immune defense involves the participation of proteins that make up the blood or other biological fluids in the formation of a protective response of the body to the attack of pathogenic microorganisms or damage. For example, immunoglobulins neutralize viruses, bacteria, or foreign proteins. Antibodies produced by the immune system attach to substances foreign to the body, called antigens, and neutralize them. As a rule, antibodies are secreted into the intercellular space or are fixed in the membranes of specialized plasma cells.

Enzymes and substrate are not interconnected too closely, otherwise the course of the catalyzed reaction may be disturbed. But the stability of the attachment of antigen and antibodies is not limited by anything.

Chemical protection consists in the binding of various toxins by protein molecules, that is, in ensuring the detoxification of the body. The most important role in the detoxification of our body is played by liver enzymes that break down poisons or convert them into a soluble form. Dissolved toxins quickly leave the body.

Regulatory function

Most intracellular processes are regulated by protein molecules. These molecules perform a highly specialized function and are neither a building material for cells nor a source of energy. Regulation is carried out due to the activity of enzymes or due to binding to other molecules.
Protein kinases play an important role in the regulation of processes inside cells. These are enzymes that affect the activity of other proteins by attaching phosphate particles to them. They either increase activity or completely suppress it.

Signal function

The signaling function of proteins is expressed in their ability to serve as signaling substances. They transmit signals between tissues, cells, organs. Sometimes the signaling function is considered similar to the regulatory one, since many regulatory intracellular proteins also carry out signaling. Cells communicate with each other using signal proteins that propagate through the intercellular substance.

Cytokines, proteins-hormones perform a signaling function.
Hormones are carried in the blood. The receptor, when bound to a hormone, triggers a response in the cell. Thanks to hormones, the concentration of substances in blood cells is regulated, as well as the regulation of cell growth and reproduction. An example of such proteins is the well-known insulin, which regulates the concentration of glucose in the blood.

Cytokines are small peptide messenger molecules. They act as regulators of the interaction between different cells, and also determine the survival of these cells, inhibit or stimulate their growth and functional activity. Without cytokines, the coordinated work of the nervous, endocrine and immune systems is impossible. For example, cytokines can cause tumor necrosis - that is, suppression of the growth and vital activity of inflammatory cells.

transport function

Soluble proteins that take part in the transport of small molecules should easily bind to the substrate if it is present in high concentration, and should also release it easily where it is in low concentration. An example of transport proteins is hemoglobin. It transports oxygen from the lungs and brings it to the rest of the tissues, and also transfers carbon dioxide back from the tissues to the lungs. Proteins similar to hemoglobin have been found in all kingdoms of living organisms.

Spare (or back-up) function

These proteins include casein, ovalbumin and others. These reserve proteins are stored in animal eggs and plant seeds as an energy source. They perform nutritional functions. Many proteins are used in our body as a source of amino acids.

Receptor function of proteins

Protein receptors can be located both in the cell membrane and in the cytoplasm. One part of the protein molecule receives a signal (of any nature: chemical, light, thermal, mechanical). The receptor protein undergoes conformational changes under the influence of a signal. These changes affect another part of the molecule, which is responsible for signal transmission to other cellular components. Signaling mechanisms differ from each other.

Motor (or motor) function

Motor proteins are responsible for ensuring the movement and contraction of muscles (at the body level) and for the movement of flagella and cilia, intracellular transport of substances, amoeboid movement of leukocytes (at the cellular level).

Proteins in metabolism

Most plants and microorganisms are able to synthesize the 20 essential amino acids, as well as some additional amino acids. But if they are in the environment, then the body will prefer to save energy and transport them inside, rather than synthesize them.

Those amino acids that are not synthesized by the body are called essential, therefore, they can only come to us from the outside.

A person receives amino acids from those proteins that are contained in food. Proteins undergo denaturation during digestion under the action of acidic gastric juices and enzymes. Some of the amino acids obtained as a result of the digestive process are used to synthesize the necessary proteins, and the rest of them are converted into glucose during gluconeogenesis or used in the Krebs cycle (this is a metabolic breakdown process).

The use of proteins as an energy source is especially important in unfavorable conditions, when the body uses the internal "untouchable reserve" - ​​its own proteins. Amino acids are also an important source of nitrogen for the body.

There are no uniform norms for the daily requirement for proteins. The microflora that inhabits the large intestine also synthesizes amino acids, and they cannot be taken into account when compiling protein norms.

The reserves of proteins in the human body are minimal, and new proteins can only be synthesized from decaying proteins coming from body tissues and from amino acids coming with food. Of those substances that are part of fats and carbohydrates, proteins are not synthesized.

Protein deficiency
The lack of protein substances in the diet causes a strong slowdown in growth and development in children. For adults, protein deficiency is dangerous due to the appearance of deep changes in the liver, changes in hormonal levels, impaired functioning of the endocrine glands, impaired absorption of nutrients, impaired memory and performance, and heart problems. All these negative phenomena are due to the fact that proteins are involved in almost all processes of the human body.

In the 70s of the last century, fatal cases were recorded in people who had been following a low-calorie diet with a pronounced protein deficiency for a long time. As a rule, the immediate cause of death in this case was irreversible changes in the heart muscle.

Protein deficiency reduces the resistance of the immune system to infections, as the level of antibody formation decreases. Violation of the synthesis of interferon and lysozyme (protective factors) causes an exacerbation of inflammatory processes. In addition, protein deficiency is often accompanied by a lack of vitamins, which in turn also leads to adverse consequences.

Deficiency affects the production of enzymes and the absorption of important nutrients. It should not be forgotten that hormones are protein formations, therefore, a lack of proteins can lead to severe hormonal disorders.

Any activity of a physical nature harms muscle cells, and the greater the load, the more the muscles suffer. To repair damaged muscle cells, you need a large amount of high-quality protein. Contrary to popular belief, physical activity is only beneficial when enough protein is supplied to the body with food. With intense physical exertion, protein intake should reach 1.5 - 2 grams per kilogram of weight.

Excess protein

To maintain the nitrogen balance in the body, a certain amount of protein is needed. If there is a little more protein in the diet, then this will not harm health. The excess amount of amino acids in this case is used simply as an additional source of energy.

But if a person does not play sports, and at the same time consumes more than 1.75 grams of protein per kilogram of weight, then an excess of protein accumulates in the liver, which is converted into nitrogenous compounds and glucose. The nitrogenous compound (urea) must be excreted by the kidneys from the body without fail.

In addition, with an excess of protein, an acidic reaction of the body occurs, which leads to a loss of calcium due to a change in the drinking regimen. In addition, protein-rich meat foods often contain purines, some of which are deposited in the joints during metabolism and cause the development of gout. It should be noted that disorders associated with excess protein are much less common than disorders associated with protein deficiency.

An assessment of a sufficient amount of protein in the diet is carried out according to the state of nitrogen balance. In the body, the synthesis of new proteins and the release of the end products of protein metabolism are constantly taking place. The composition of proteins includes nitrogen, which is not contained in either fats or carbohydrates. And if nitrogen is deposited in the body in reserve, it is exclusively in the composition of proteins. With protein breakdown, it should stand out along with the urine. In order for the functioning of the body to be carried out at the desired level, it is necessary to replenish the removed nitrogen. Nitrogen balance means that the amount of nitrogen consumed matches the amount excreted from the body.

Protein nutrition

The benefits of dietary proteins are evaluated by the coefficient of protein digestibility. This coefficient takes into account the chemical value (composition of amino acids), and the biological value (percentage of protein digestion). Complete protein sources are those foods that have a digestibility factor of 1.00.

The digestibility factor is 1.00 in the following foods: eggs, soy protein, milk. Beef shows a coefficient of 0.92.

These products are a high-quality source of protein, but you need to remember that they contain a lot of fat, so it is undesirable to abuse their frequency in the diet. In addition to a large amount of protein, an excessive amount of fat will also enter the body.

Preferred high-protein foods: soy cheeses, low-fat cheeses, lean veal, egg whites, low-fat cottage cheese, fresh fish and seafood, lamb, chicken, white meats.
Less preferred foods are: milk and yoghurt with added sugar, red meat (tenderloin), dark chicken and turkey meat, low-fat cuts, homemade cottage cheese, processed meat in the form of bacon, salami, ham.

Egg white is a pure protein with no fat. Lean meat contains about 50% of the kilocalories that come from protein; in products containing starch - 15%; in skim milk - 40%; in vegetables - 30%.

The main rule when choosing a protein diet is as follows: more protein per calorie unit and a high protein digestibility ratio. It is best to consume foods that are low in fat and high in protein. Calorie data can be found on the packaging of any product. Generalized data on the content of proteins and fats in those products whose calorie content is difficult to calculate can be found in special tables.

Heat-treated proteins are easier to digest, as they become readily available for the action of digestive tract enzymes. However, heat treatment can reduce the biological value of the protein due to the fact that some amino acids are destroyed.

The content of proteins and fats in some foods

Products	Proteins, grams	Fats, grams
Chicken	20,8	8,9
Heart	15	3
Lean pork	16,3	27,8
Beef	18,9	12,3
Veal	19,7	1,2
Doctor's boiled sausage	13,7	22,9
Diet boiled sausage	12,2	13,5
pollock	15,8	0,7
Herring	17,7	19,6
Sturgeon caviar granular	28,6	9,8
Wheat bread from flour I grade	7,6	2,3
Rye bread	4,5	0,8
Sweet pastries	7,2	4,3

It is very useful to consume soy products: tofu cheese, milk, meat. Soy contains absolutely all the necessary amino acids in such a ratio that is necessary to meet the needs of the body. In addition, it is well absorbed.
The casein found in milk is also a complete protein. Its digestibility coefficient is 1.00. The combination of casein isolated from milk and soy makes it possible to create healthy foods with a high protein content, while they do not contain lactose, which allows them to be consumed by persons suffering from lactose intolerance. Another plus of such products is that they do not contain whey, which is a potential source of allergens.

Protein metabolism

To absorb protein, the body needs a lot of energy. First of all, the body must break down the amino acid chain of the protein into several short chains, or into the amino acids themselves. This process is quite lengthy and requires different enzymes that the body must create and transport into the digestive tract. Residual products of protein metabolism - nitrogenous compounds - must be removed from the body.


All these actions in total consume a considerable amount of energy for the absorption of protein foods. Therefore, protein food stimulates the acceleration of metabolism and an increase in energy costs for internal processes.

The body can spend about 15% of the total caloric content of the diet on the assimilation of food.
Food with a high protein content, in the process of metabolism, contributes to increased heat production. Body temperature slightly increases, which leads to additional energy consumption for the process of thermogenesis.

Proteins are not always used as an energy substance. This is due to the fact that their use as an energy source for the body can be unprofitable, because from a certain amount of fats and carbohydrates you can get much more calories and much more efficiently than from a similar amount of protein. In addition, there is rarely an excess of proteins in the body, and if there is, then most of the excess proteins go to carry out plastic functions.

In the event that the diet lacks energy sources in the form of fats and carbohydrates, the body is taken to use the accumulated fats.

A sufficient amount of protein in the diet helps to activate and normalize a slow metabolism in those people who are obese, and also helps maintain muscle mass.

If there is not enough protein, the body switches to using muscle proteins. This is because the muscles are not so important for the maintenance of the body. Most of the calories are burned in muscle fibers, and a decrease in muscle mass reduces the body's energy costs.

Very often, people who follow various diets for weight loss choose a diet in which very little protein enters the body with food. As a rule, these are vegetable or fruit diets. In addition to harm, such a diet will not bring anything. The functioning of organs and systems with a lack of proteins is inhibited, which causes various disorders and diseases. Each diet should be considered in terms of the body's need for protein.

Processes such as the absorption of proteins and their use in energy needs, as well as the excretion of products of protein metabolism, require more fluid. In order not to get dehydrated, you need to take about 2 liters of water per day.

Proteins and their functions.

We will study the main substances that make up our organisms. One of the most important is proteins.

Squirrels(proteins, polypeptides) - carbon substances, consisting of chain-linked amino acids. They are an essential part of all cells.

Amino acids- carbon compounds, the molecules of which simultaneously contain carboxyl (-COOH) and amine (NH2) groups.

A compound consisting of a large number of amino acids is called - polypeptide. Each protein in its chemical structure is a polypeptide. Some proteins are made up of several polypeptide chains. Most proteins contain an average of 300-500 amino acid residues. Several very short natural proteins, 3-8 amino acids long, and very long biopolymers, more than 1500 amino acids long, are known.

The properties of proteins determine their amino acid composition, in a strictly fixed sequence, and the amino acid composition, in turn, is determined by the genetic code. When creating proteins, 20 standard amino acids are used.

The structure of proteins.

There are several levels:

- Primary structure - determined by the order of alternation of amino acids in the polypeptide chain.

Twenty different amino acids can be likened to 20 letters of the chemical alphabet, which make up "words" 300-500 letters long. With 20 letters, you can write an unlimited number of such long words. If we consider that the replacement or rearrangement of at least one letter in a word gives it a new meaning, then the number of combinations in a word 500 letters long will be 20500.

It is known that the replacement of even one amino acid unit by another in a protein molecule changes its properties. Each cell contains several thousand different types of protein molecules, and each of them is characterized by a strictly defined sequence of amino acids. It is the order of alternation of amino acids in a given protein molecule that determines its special physicochemical and biological properties. Researchers are able to decipher the sequence of amino acids in long protein molecules and synthesize such molecules.

- secondary structure- protein molecules in the form of a spiral, with equal distances between the turns.

Hydrogen bonds arise between the N-H and C=O groups located on adjacent turns. They are repeated many times, fasten the regular turns of the spiral.

- Tertiary structure- the formation of a spiral coil.

This tangle is formed by the regular interlacing of sections of the protein chain. Positively and negatively charged groups of amino acids attract and bring together even widely spaced parts of the protein chain. Other parts of the protein molecule, carrying, for example, “water-repellent” (hydrophobic) radicals, also approach each other.

Each type of protein is characterized by its own shape of a ball with bends and loops. The tertiary structure depends on the primary structure, that is, on the order of the amino acids in the chain.
- Quaternary structure- assembly protein consisting of several chains that differ in primary structure.
Combining together, they create a complex protein that has not only a tertiary, but also a quaternary structure.

protein denaturation.

Under the influence of ionizing radiation, high temperature, strong agitation, extreme pH values ​​(concentration of hydrogen ions), as well as a number of organic solvents such as alcohol or acetone, proteins change their natural state. Violation of the natural structure of the protein is called denaturation. The vast majority of proteins lose their biological activity, although their primary structure does not change after denaturation. The fact is that in the process of denaturation, secondary, tertiary and quaternary structures are violated, due to weak interactions between amino acid residues, and covalent peptide bonds (with the union of electrons) do not break. Irreversible denaturation can be observed when liquid and transparent chicken egg protein is heated: it becomes dense and opaque. Denaturation can also be reversible. After elimination of the denaturing factor, many proteins are able to return to their natural form, i.e. renature.

The ability of proteins to reversibly change the spatial structure in response to the action of physical or chemical factors underlies irritability, the most important property of all living beings.

Protein functions.

catalytic.

Hundreds of biochemical reactions take place continuously in every living cell. During these reactions, the splitting and oxidation of nutrients coming from outside take place. The energy of nutrients obtained as a result of oxidation and the products of their breakdown are used by the cell to synthesize the various organic compounds it needs. The rapid occurrence of such reactions is provided by biological catalysts, or reaction accelerators - enzymes. More than a thousand different enzymes are known. They are all white.
Protein enzymes - speed up reactions in the body. Enzymes are involved in the breakdown of complex molecules (catabolism) and their synthesis (anabolism), as well as the creation and repair of DNA and RNA template synthesis.

Structural.

Structural proteins of the cytoskeleton, like a kind of armature, give shape to cells and many organelles and are involved in changing the shape of cells. Collagen and elastin are the main components of the intercellular substance of connective tissue (for example, cartilage), and hair, nails, bird feathers, and some shells are made up of another structural protein, keratin.

Protective.

1. Physical protection.(example: collagen is a protein that forms the basis of the intercellular substance of connective tissues)

1. Chemical protection. The binding of toxins to protein molecules ensures their detoxification. (example: liver enzymes that break down poisons or convert them into a soluble form, which contributes to their rapid removal from the body)

1. Immune protection. When bacteria or viruses enter the blood of animals and humans, the body reacts by producing special protective proteins - antibodies. These proteins bind to proteins of pathogens that are foreign to the body, which suppresses their vital activity. For each foreign protein, the body produces special "anti-proteins" - antibodies.

Regulatory.

Hormones are carried in the blood. Most animal hormones are proteins or peptides. The binding of the hormone to the receptor is a signal that triggers a response in the cell. Hormones regulate the concentration of substances in the blood and cells, growth, reproduction and other processes. An example of such proteins is insulin which regulates the concentration of glucose in the blood.

Cells interact with each other using signal proteins transmitted through the intercellular substance. Such proteins include, for example, cytokines and growth factors.

Cytokines- small peptide information molecules. They regulate interactions between cells, determine their survival, stimulate or suppress growth, differentiation, functional activity and programmed cell death, ensure the coordination of actions of the immune, endocrine and nervous systems.

Transport.

Only proteins transport substances in the blood, for example, lipoproteins(fat transfer) hemoglobin(oxygen transport), transferrin(iron transport) or across membranes - Na +, K + -ATPase(opposite transmembrane transport of sodium and potassium ions), Ca2+-ATPase(pumping calcium ions out of the cell).

Receptor.

Protein receptors can either be located in the cytoplasm or integrated into the cell membrane. One part of the receptor molecule receives a signal, most often a chemical substance, and in some cases, light, mechanical action (for example, stretching), and other stimuli.

Construction.

Animals in the process of evolution have lost the ability to synthesize ten particularly complex amino acids, called essential. They get them ready-made with plant and animal food. Such amino acids are found in the proteins of dairy products (milk, cheese, cottage cheese), in eggs, fish, meat, as well as in soybeans, beans and some other plants. In the digestive tract, proteins are broken down into amino acids, which are absorbed into the bloodstream and enter the cells. In cells, from ready-made amino acids, their own proteins are built, which are characteristic of a given organism. Proteins are an essential component of all cellular structures and this is their important building role.

Energy.

Proteins can serve as a source of energy for the cell. With a lack of carbohydrates or fats, amino acid molecules are oxidized. The energy released in this process is used to support the vital processes of the body. With prolonged fasting, proteins of muscles, lymphoid organs, epithelial tissues and liver are used.

Motor (motor).

A whole class of motor proteins provides for the movements of the body, for example, muscle contraction, including the movement of myosin bridges in the muscle, the movement of cells within the body (for example, the amoeboid movement of leukocytes).

In fact, this is a very brief description of the functions of proteins, which can only clearly demonstrate their functions and significance in the body.

A little video for understanding about proteins: