Types of proteins, their functions and structure

According to Oparin-Haldane theory, life on our planet originated from a coacervate droplet. It was a protein molecule. That is, it follows that these chemical compounds are the basis of all living things that exist today. But what are the protein structures? What role do they play today in the body and people's lives? What kinds of proteins exist? Let's try to understand.

Proteins: a general concept

From the point of view of the chemical structure, the molecule of the substance in question is a sequence of amino acids linked together by peptide bonds.

Each amino acid has two functional groups:

• Carboxyl-COOH;
• Amino group -NH ₂ .

It is between them that the formation of a bond in different molecules takes place. Thus, the peptide bond has the form -CO-NH. A protein molecule can contain hundreds and thousands of such groups, this will depend on the particular substance. The types of proteins are very diverse. Among them, there are those that contain amino acids that are irreplaceable for the body, and therefore must enter the body with food. There are such varieties that perform important functions in the cell membrane and its cytoplasm. Biological nature catalysts are also isolated - enzymes, which are also protein molecules. They are widely used and in the life of man, and not only participate in the biochemical processes of living beings.

The molecular weight of the compounds in question can range from several tens to millions. After all, the number of monomeric units in a large polypeptide chain is unlimited and depends on the type of the particular substance. Protein in its pure form, in its native conformation, can be seen when considering a chicken egg in its raw form. A light yellow, transparent, thick colloidal mass, inside which the yolk is located, is the desired substance. The same thing to say about low-fat cottage cheese, This product is also almost pure protein in its natural form.

However, not all considered compounds have the same spatial structure. In total, four organization of the molecule. Types of protein structures determine its properties and speak about the complexity of the structure. It is also known that more spatially entangled molecules undergo thorough processing in the human body and animals.

Types of protein structures

There are four in all. Let us consider what each of them represents.

1. Primary. It is the usual linear sequence of amino acids linked by peptide bonds. No spatial twists, no spiral. The number of polypeptide elements entering into the polypeptide can reach several thousand. Types of proteins with a similar structure - glycylalanine, insulin, histones, elastin and others.
2. Secondary. It is two polypeptide chains that twist in the form of a spiral and are oriented towards each other by the formed turns. At the same time, hydrogen bonds form between them, holding them together. So a single protein molecule is formed. Types of proteins of this type are the following: lysozyme, pepsin and others.
3. Tertiary conformation. It is a densely packed and compactly assembled secondary structure. Here there are other types of interaction, 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, consisting of several polypeptide chains twisted into a spiral, rolled up into a ball and combined together into a globule. Examples such as insulin, ferritin, hemoglobin, collagen, illustrate just such a conformation of proteins.

If we consider all the given molecular structures in detail from a chemical point of view, then the analysis will take a long time. In fact, the higher the configuration, the more complex and complicated 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 degrade under the influence of certain conditions or chemical agents. For example, different types of denaturation of proteins 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 destruction of the conformation? There are several such.

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

This process is sometimes also called melting of a molecule. The types of denaturation of proteins depend on the agent under whose action it occurred. In this case, in some cases, there is a process inverse to the one considered. It's renaturation. Not all proteins are able to restore their structure back, but a significant part of them can do this. Thus, chemists from Australia and America performed renaturation of boiled chicken eggs with the help of some reagents and a method of centrifugation.

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

Hydrolysis of the Protein Molecule

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

1. Chemical. It is 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 kinds 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 specific organism.

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

Functions of proteins in the body

Different types of proteins, carbohydrates, fats are vital components for normal vital activity of any cell. And that means the whole organism as a whole. Therefore, in many respects, their role is explained by the high degree of significance and widespread prevalence within living beings. Several basic functions of polypeptide molecules can be distinguished.

1. Catalytic. It is carried out by enzymes, which have the protein nature of the structure. About them we will tell 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, the polypeptides that perform this role form hair, nails, shells of mollusks, feathers of birds. They are a specific armature in the body of the cell. Cartilages are also composed 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 of the 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 the communication of tissues among themselves. 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 carries oxygen from the cell to the cell in the blood. For man it is indispensable.
6. Spare or backup. Such polypeptides accumulate in plants and ovum animals as a source of additional nutrition and energy. An example is globulins.
7. Motor. 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 organoids by their nature are nothing but proteins. Examples of such polypeptides are the following: myosin, actin, kinesin and the like.

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

Protective function of proteins

Polypeptides can protect against various effects: chemical, physical, biological. For example, if an organism is threatened with a virus or a bacterium having an alien nature, then immunoglobulins (antibodies) enter into battle with them, performing a protective role.

If we talk about physical effects, then a great role is played, for example, by fibrin and fibrinogen, which are involved in blood clotting.

Protein food

The types of food protein are as follows:

• Full-fledged - those that contain all the amino acids necessary for the body;
• Inferior - those in which the partial amino acid composition is located.

However, for the human body, both are important. Especially the first group. Everyone, especially during periods of intense development (childhood and adolescence) and puberty should maintain a constant level of proteins in themselves. After all, we have already examined the functions that these amazing molecules perform, and we know that virtually no process, no biochemical reaction inside of us can do without the participation of polypeptides.

That is why every day you need to consume the daily norm of proteins, which are contained in the following products:

• egg;
• milk;
• cottage cheese;
• Meat and fish;
• Beans;
• Soybeans;
• Beans;
• peanut;
• wheat;
• Oats;
• Lentils and others.

If you consume 0.6 g of polypeptide per day per kilogram of weight per day, then a person will never have a shortage of these compounds. If, for a long time, the body lacks the necessary proteins, then there comes a disease called amino acid starvation. This leads to a strong disruption of metabolism and, as a result, many other ailments.

Proteins in a cage

Within the smallest structural unit of all living things-cells-there are also proteins. And they perform almost all of the above functions. First of all, a cytoskeleton of a cell consisting of microtubules, microfilaments is formed. It serves to maintain the shape, as well as for transport inside the organelles. On protein molecules, as through channels or rails, various ions and compounds move.

Important role of proteins immersed in the membrane and located on its surface. Here they both receptor and signal functions perform, take part in the construction of the membrane itself. Are on guard, and therefore play a protective role. What kinds of proteins in the cell can be attributed to this group? There are many examples, we give 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 types of proteins that constantly move inside each cell.

Types of proteins in the body

They, of course, a huge variety. If you try to somehow divide all existing proteins into groups, then this classification may turn out.

1. Globular proteins. These are those that are represented by a tertiary structure, that is, a tightly packed globule. Examples of such structures are: immunoglobulins, a significant part of enzymes, many hormones.
2. Fibrillar proteins. They are strictly ordered threads that have the correct spatial symmetry. This group includes proteins with a primary and secondary structure. For example, keratin, collagen, tropomyosin, fibrinogen.

In general, it is possible to take as a basis many features for the classification of proteins found in the body. Single yet does not exist.

Enzymes

Biological catalysts of protein nature, which greatly accelerate all the ongoing biochemical processes. Normal metabolism is simply impossible without these compounds. All processes of synthesis and decomposition, 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:

• Oxidoreductase;
• Transferase;
• Catalase;
• Hydrolases;
• Isomerase;
• Lyases and others.

Today, enzymes are used in everyday life. So, when manufacturing detergent powders, so-called enzymes are often used - these are biological catalysts. They improve the quality of washing under the specified temperature conditions. Easily bind to particles of dirt and remove them from the surface of tissues.

However, because of the protein nature, enzymes do not tolerate too hot water or proximity to alkaline or acidic drugs. In this case, a process of denaturation will occur.