Monomers of proteins are what substances? What are protein monomers?

Proteins are biological polymers with a complex structure. They have a high molecular weight and consist of amino acids, prosthetic groups represented by vitamins, lipid and carbohydrate inclusions. Proteins that contain carbohydrates, vitamins, metals or lipids are called complex. Simple proteins consist of only amino acids linked together by a peptide bond.

Peptides

Regardless of the structure of the substance, amino acids are monomers of proteins. They form a basic polypeptide chain, from which the fibrillar or globular structure of the protein is then formed. In this case, the protein can be synthesized only in living tissue - in plant, bacterial, fungal, animal and other cells.

The only organisms that can not combine protein monomers are viruses and protozoa. All the others are capable of forming structural proteins. But what substances are monomers of proteins, and how are they formed? About this and about protein biosynthesis, about polypeptides and the formation of a complex protein structure, about amino acids and their properties, read below.

The only monomer of the protein molecule is any alpha-amino acid. In this case, the protein is a polypeptide, a chain of connected amino acids. Depending on the amount of amino acids involved in its formation, dipeptides (2 residues), tripeptides (3), oligopeptides (contains from 2-10 amino acids) and polypeptides (many amino acids) are isolated.

Review of the structure of proteins

The structure of the protein can be primary, slightly more complex - secondary, even more complex - tertiary, and the most complex - Quaternary.

The primary structure is a simple chain into which monomers of proteins (amino acids) are connected through a peptide bond (CO-NH). The secondary structure is an alpha helix or a beta fold. Tertiary is an even more complicated three-dimensional structure of the protein, which was formed from the secondary due to the formation of covalent, ionic and hydrogen bonds, as well as hydrophobic interactions.

The quaternary structure is the most complex and is characteristic of receptor proteins located on cell membranes. This is a supramolecular (domain) structure formed by combining several molecules with a tertiary structure, supplemented with carbohydrate, lipid or vitamin groups. In this case, as in the primary, secondary and tertiary structures, the protein monomers are alpha-amino acids. They are also linked by peptide bonds. The only difference is the complexity of the structure.

Amino acids

The only monomers of protein molecules are alpha-amino acids. They are only 20, and they are almost the basis of life. Thanks to the appearance of a peptide bond, protein synthesis became possible. And the protein itself after that began to perform the structure-forming, receptor, enzymatic, transport, mediator and other functions. Thanks to this, the living organism functions and is able to reproduce.

The alpha-amino acid itself is an organic carboxylic acid with an amino group linked to an alpha-carbon atom. The latter is located next to the carboxyl group. In this case, protein monomers are considered as organic substances in which the terminal carbon atom carries both an amine and a carboxyl group.

The combination of amino acids in peptides and proteins

Amino acids are combined in dimers, trimers and polymers through a peptide bond. It is formed by cleavage of the hydroxyl (-OH) group from the carboxyl portion of one alpha-amino acid and hydrogen (-H) - from the amino group of the other alpha-amino acid. As a result of the interaction, water is split off, and at the carboxyl end there remains a C = O region with a free electron near the carbon of the carboxyl residue. In the amino group of the other acid, there is a (NH) residue with an available free radical at the nitrogen atom. This allows two radicals to be joined together to form a bond (CONH). It is called peptide.

Variants of alpha-amino acids

In total 23 alpha-amino acids are known. They are presented in the form of a list: glycine, valine, alanine, isoleucine, leucine, glutamate, asparaginate, ornithine, threonine, serine, lysine, cystine, cysteine, phenylalanine, methionine, tyrosine, proline, tryptophan, hydroxyproline, arginine, histidine, asparagine and glutamine. Depending on whether they can be synthesized by the human body, these amino acids are divided into interchangeable and irreplaceable.

The concept of interchangeable and essential amino acids

Replaceable human body can synthesize, while the irreplaceable must come only with food. In this case, both essential and replaceable acids are important for protein biosynthesis, because without them synthesis can not be completed. Without one amino acid, even if all the others are present, it is impossible to build exactly the protein that the cell requires to perform its functions.

One error at any stage of biosynthesis - and the protein is already unsuitable, because it can not gather in the desired structure due to violation of electronic densities and interatomic interactions. Therefore, it is important for a person (and other organisms) to consume protein foods, in which there are essential amino acids. Their absence in food leads to a number of violations of protein metabolism.

The process of peptide bond formation

The only monomers of proteins are alpha-amino acids. They gradually combine into a chain of polypeptides, the structure of which is pre-stored in the genetic code of DNA (or RNA, if bacterial biosynthesis is considered). In this case, the protein is a strict sequence of amino acid residues. This is a chain, ordered in a specific structure, which performs a preprogrammed function in the cell.

Step sequence of protein biosynthesis

The process of protein formation consists of a chain of steps: the replication of the DNA (or RNA) region, the synthesis of RNA of the informational type, its release into the cytoplasm of the cell from the nucleus, the connection with the ribosome and the gradual attachment of the amino acid residues that are supplied by the transport RNA. The substance, which is a monomer of the protein, participates in the enzymatic reaction of the elimination of the hydroxyl group and the hydrogen proton, and then joins the escalating polypetic chain.

Thus, a polypeptide chain is obtained which, already in the cellular endoplasmic reticulum, is ordered into a predetermined structure and supplemented with a carbohydrate or lipid residue, if required. This is called the "maturation" of the protein, after which it is sent by the transport cellular system to the destination.

Functions of synthesized proteins

Monomers of proteins are the amino acids necessary for constructing their primary structure. The secondary, tertiary and quaternary structure already forms itself, although sometimes it also requires the participation of enzymes and other substances. However, they are no longer basic, although it is essential that proteins fulfill their function.

The amino acid, which is a monomer of the protein, can have attachment sites for carbohydrates, metals or vitamins. The formation of a tertiary or quaternary structure makes it possible to find even more places for the arrangement of intercalary groups. This makes it possible to create from a protein a derivative that plays the role of an enzyme, a receptor, a carrier of substances into or out of the cell, an immunoglobulin, a structural component of a membrane or a cell organelle, a muscle protein.

Proteins, formed from amino acids, are the only basis of life. And today it is believed that life was born after the appearance of the amino acid and its polymerization. After all, the intermolecular interaction of proteins is the beginning of life, including the rational one. All other biochemical processes, including energy, are necessary for the realization of protein biosynthesis, and as a result, the further continuation of life.