Types of proteins, their functions and structure

According to the theory of Oparin-Haldane, life on our planet originated from a coacervate droplet. She 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 protein structures? What role do they play today in the human body and life? What types of proteins exist? Let's try to figure it out.

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 interconnected by peptide bonds.

Each amino acid has two functional groups:

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

It is between them that a bond is formed in different molecules. Thus, the peptide bond has the form —CO — NH. A protein molecule can contain hundreds and thousands of such groups, it will depend on the specific substance. Types of proteins are very diverse. Among them are those that contain amino acids essential 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. Catalysts of a biological nature 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 in question can range 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 specific substance. Protein in its pure form, in its native conformation, can be seen when considering a raw chicken egg . A light yellow, transparent thick dense colloidal mass, inside of which the yolk is located - this is the desired substance. The same is true for low-fat 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. The types of protein structures determine its properties and indicate the complexity of the structure. It is also known that more spatially entangled molecules undergo careful processing in humans and animals.

Types of protein structures

In total, four of them are distinguished. Consider what each of them is.

1. Primary It is an ordinary linear sequence of amino acids connected by peptide bonds. There are no spatial twists, no spiralization. The number of links in 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 are twisted in a spiral and are oriented towards each other by formed coils. In this case, hydrogen bonds arise between them, holding them together. Thus a single protein molecule is formed. Types of proteins of this type are as follows: lysozyme, pepsin and others.
3. Tertiary conformation. It is a tightly packed and compactly bundled 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 consists of several polypeptide chains twisted into a spiral, coiled 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 above molecular structures 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 complicated and confused its structure, the more types of interactions are observed in the molecule.

Protein denaturation

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 protein structure. That is, if initially the molecule had a tertiary structure, then after the action of special agents it will be destroyed. 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 destruction of conformation? There are several of them.

1. Temperature. When heated, a gradual destruction of the quaternary, tertiary, secondary structure of the molecule occurs. 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. 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 the melting of a molecule. Types of protein denaturation depend on the agent upon which it occurred. Moreover, in some cases, the process opposite to the one considered takes place. This is a 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 renatured boiled chicken eggs 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, another chemical property is characteristic of proteins - hydrolysis. It 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 hydrolysis of proteins take place. As a result, amino acids are formed that are transported throughout 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 obtain the desired amino acids.

The 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, in many respects their role is explained by a high degree of significance and widespread prevalence within living beings. Several main functions of polypeptide molecules can be distinguished.

1. Catalytic. It is carried out by enzymes that have a protein nature of the structure. We will talk about them later.
2. Structural. Types of proteins and their functions in the body primarily affect the structure of the cell itself, its shape. In addition, polypeptides playing this role form hair, nails, mollusk shells, and feathers of birds. They are a certain armature in the body of the cell. Cartilage also consists 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, reading of mRNA and others. In all of them, they play an important role as a traffic controller.
4. Signal. This function is performed by proteins located on the cell membrane. They transmit various signals from one unit to another, and this leads to the message of tissues between 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 hemoglobin protein. It carries out oxygen transport from cell to cell in the blood. For a person, it is indispensable.
6. Spare or standby. Such polypeptides accumulate in animal plants and eggs as a source of additional nutrition and energy. An example is globulins.
7. Propulsion. A very important function, especially for protozoa and bacteria. After all, they are able to move only with the help of flagella or cilia. And these organelles are by nature nothing more than proteins. Examples of such polypeptides are as follows: 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.

Protein protective function

Polypeptides can protect against various effects: chemical, physical, biological. For example, if the body is in danger in the form of a virus or bacteria of a foreign nature, then immunoglobulins (antibodies) come 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:

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

However, both are important for the human body. Especially the first group. Everyone, especially during periods of intensive development (childhood and adolescence) and puberty should maintain a constant level of protein in themselves. After all, we have already examined the functions that these amazing molecules perform, and we know that practically no process, not a single biochemical reaction within us is complete without the participation of polypeptides.

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

• 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 kg of weight per day, then a person will never have a lack of these compounds. If, for a long time, the body does not receive the necessary proteins, then a disease called amino acid starvation sets in. This leads to a severe metabolic disorder and, as a consequence, many other ailments.

Proteins in a cage

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 cell cytoskeleton is formed, consisting of microtubules, microfilaments. It serves to maintain shape, as well as for transport within between organoids. Along protein molecules, like channels or rails, various ions and compounds move.

An important role is played by proteins immersed in the membrane and located on its surface. Here they fulfill both receptor and signaling 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 a 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 types of proteins that constantly move inside each cell.

Types of proteins in the body

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

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

In general, many signs can be taken as a basis for the classification of proteins in the body. One does not exist yet.

Enzymes

Biological catalysts of protein nature, which significantly accelerate all ongoing biochemical processes. Normal metabolism is simply not possible 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;
• isomerase;
• lyases and others.

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

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