What does the protein consist of? Examples of simple and complex proteins

To imagine the importance of proteins, it is enough to recall the well-known phrase of Friedrich Engels: "Life is a way of existence of protein bodies." In fact, on the Earth these substances along with nucleic acids cause all manifestations of living matter. In this paper, we will find out what the protein consists of, we will study what function it performs, and also we will determine the features of the structure of various species.

Peptides - highly organized polymers

Indeed, in a living cell, both plant and animal, proteins predominate over other organic substances, and also perform the greatest number of diverse functions. They participate in a variety of very important cellular processes, such as movement, defense, signaling, and so on. For example, in the muscle tissue of animals and humans, peptides constitute up to 85% of the dry matter mass, and in the bone and dermis, from 15-50%.

All cellular and tissue proteins consist of amino acids (20 species). Their number in living organisms is always twenty kinds. Various combinations of peptide monomers form a variety of proteins in nature. It is calculated by an astronomical number of 2x10 ¹⁸ possible species. In biochemistry, polypeptides are called high molecular biological polymers, macromolecules.

Amino acids - monomers of proteins

All 20 kinds of these chemical compounds are structural units of proteins and have the general formula NH ₂ -R-COOH. They are amphoteric organic substances capable of exhibiting both basic and acidic properties. Not only simple proteins, but also complex ones, contain so-called non-essential amino acids. But indispensable monomers, for example, such as valine, lysine, methionine can be found only in some types of proteins. Such proteins are called full.

Therefore, characterizing the polymer takes into account not only how many amino acids the protein consists of, but also which monomers are connected by peptide bonds to the macromolecule. We also add that interchangeable amino acids, such as asparagine, glutamic acid, cysteine can be synthesized independently in human and animal cells. Irreplaceable protein monomers are formed in cells of bacteria, plants and fungi. They enter heterotrophic organisms only with food.

How the polypeptide is formed

As you know, 20 different amino acids can be combined into many different protein molecules. How does the binding of monomers occur among themselves? It turns out that the carboxyl and amine groups of a number of lying amino acids interact with each other. So-called peptide bonds are formed, and water molecules are released as a by-product of the polycondensation reaction. The protein molecules formed consist of amino acid residues and repeatedly recurring peptide bonds. Therefore they are also called polypeptides.

Often, proteins can contain not one but several polypeptide chains and consist of many thousands of amino acid residues. Moreover, simple proteins, as well as proteids, can complicate their spatial configuration. This creates not only a primary, but also a secondary, tertiary and even quaternary structure. Let us consider this process in more detail. Continuing to study the question: what does the protein consist of, what is the configuration of this macromolecule. We have established above that the polypeptide chain contains a number of covalent chemical bonds. It is this structure that is called primary.

It plays an important role in the quantitative and qualitative composition of amino acids, as well as the sequence of their connection. Secondary structure occurs at the time of formation of the spiral. It is stabilized by many newly emerging hydrogen bonds.

Higher levels of protein organization

The tertiary structure appears as a result of packaging a spiral in the form of a globule, for example, the muscle protein protein myoglobin has just such a spatial structure. It is maintained by both newly formed hydrogen bonds and disulfide bridges (if several cysteine residues enter the protein molecule). The quaternary form is the result of combining several protein globules into a single structure at once by means of new types of interactions, for example, hydrophobic or electrostatic. Along with peptides, non-protein parts also enter the quaternary structure. They can be ions of magnesium, iron, copper, or residues of orthophosphate or nucleic acids, as well as lipids.

Features of protein biosynthesis

Previously, we found out what the protein consists of. It is constructed from a sequence of amino acids. Their assembling into a polypeptide chain occurs in ribosomes - non-membrane organelles of plant and animal cells. Molecules of information and transport RNA also participate in the process of biosynthesis. The first are the matrix for protein assembly, and the second transport various amino acids. In the process of cellular biosynthesis, a dilemma arises, namely, does the protein consist of nucleotides or amino acids? The answer is unambiguous - polypeptides, both simple and complex, consist of amphoteric organic compounds - amino acids. In the life cycle of the cell, there are periods of its activity, when the synthesis of proteins is particularly active. These are the so-called stages J1 and J2 of the interphase. At this time, the cell is actively growing and needs a lot of building material, which is protein. In addition, as a result of mitosis, which ends with the formation of two daughter cells, each of them needs a large amount of organic substances, therefore active channels of lipids and carbohydrates are synthesized on the channels of the smooth endoplasmic reticulum, and protein biosynthesis occurs on the granular EPS.

Functions of proteins

Knowing what the protein consists of, one can explain both the huge variety of their species and the unique properties inherent in these substances. Proteins perform a variety of functions in the cell, for example, construction, as they are part of the membranes of all cells and organoids: mitochondria, chloroplasts, lysosomes, the Golgi complex, and so on. Such peptides as gamoglobulins or antibodies are examples of simple proteins that perform a protective function. In other words, cellular immunity is the result of the action of these substances. Complex protein - hemocyanin, along with hemoglobin, performs in animals the transport function, that is, carries oxygen in the blood. Signal proteins, which are part of cell membranes, provide information to the cell itself about substances that try to get into its cytoplasm. Peptide albumin is responsible for the basic blood parameters, for example, for its ability to clot. Protein of chicken eggs ovalbumin is stored in a cage and serves as the main source of nutrients.

Proteins are the basis of the cell's cytoskeleton

One of the important functions of peptides is the supporting one. It is very important for preserving the shape and volume of living cells. The so-called sub-membrane structures - microtubules and micro-filaments interweaving form the inner skeleton of the cell. The proteins that make up their composition, for example, tubulin, can easily contract and stretch. This helps the cell to maintain its shape under various mechanical deformations.

In plant cells, along with the proteins of the hyaloplasm, the cytoplasmic tracts - plasmodesmas also carry a supporting function. Passing through the pores in the cell wall, they cause the relationship between a number of lying cellular structures forming plant tissue.

Enzymes are substances of protein nature

One of the most important properties of proteins is their effect on the rate of chemical reactions. The main proteins are capable of partial denaturation - the process of unwinding the macromolecule in the tertiary or quaternary structure. The polypeptide chain itself does not break down. Partial denaturation underlies both the signal and catalytic functions of the protein. The last property is the ability of enzymes to influence the rate of biochemical reactions in the nucleus and the cytoplasm of the cell. Peptides, which, on the contrary, reduce the speed of chemical processes are usually called not inhibitors, but enzymes. For example, a simple catalase protein is an enzyme that accelerates the cleavage of the toxic substance of hydrogen peroxide. It is formed as the final product of many chemical reactions. Catalase accelerates its utilization to neutral substances: water and oxygen.

Properties of proteins

Peptides are classified by many features. For example, in relation to water, they can be divided into hydrophilic and hydrophobic. Temperature also affects the structure and properties of protein molecules in different ways. For example, the protein keratin - a component of nails and hair can withstand both low and high temperatures, that is, it is thermolabile. But the protein ovalbumin, already mentioned earlier, when heated to 80-100 ° C completely destroyed. This means that its primary structure is split into amino acid residues. This process is called destruction. Whatever conditions we create, the protein can not return to the native form. Motor proteins - actin and milosin are present in muscle fibers. Their alternate reduction and relaxation lies at the heart of the work of the muscle tissue.