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 containing carbohydrates, vitamins, metals or lipids are called complex. Simple proteins consist only of amino acids linked by peptide bonds.
Peptides
Regardless of what structure a substance has, the monomers of proteins are amino acids. They form the basic polypeptide chain, from which the fibrillar or globular structure of the protein is then formed. At the same time, protein can only be synthesized in living tissue - in plant, bacterial, fungal, animal and other cells.
The only organisms that cannot combine protein monomers are viruses and protozoa. All others are capable of forming structural proteins. But what substances are protein monomers, and how are they formed? Read about this and about protein biosynthesis, about polypeptides and the formation of a complex protein structure, about amino acids and their properties.below.
The only monomer of a protein molecule is any alpha-amino acid. A protein is a polypeptide, a chain of linked amino acids. Depending on the number 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.
Protein structure review
Protein structure 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 protein monomers (amino acids) are connected through a peptide bond (CO-NH). The secondary structure is the alpha helix or beta folds. Tertiary is an even more complicated three-dimensional protein structure, 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 as a result of the combination of several molecules with a tertiary structure, supplemented with carbohydrate, lipid or vitamin groups. In this case, as in the case of primary, secondary, and tertiary structures, the monomers of proteins are alpha-amino acids. They are also connected by peptide bonds. The only difference is the complexity of the structure.
Amino acids
The only monomersprotein molecules are alpha amino acids. There are only 20 of them, and they are almost the basis of life. Thanks to the appearance of the peptide bond, protein synthesis became possible. And the protein itself after that began to perform structure-forming, receptor, enzymatic, transport, mediator and other functions. Thanks to this, a living organism functions and is able to reproduce.
The alpha amino acid itself is an organic carboxylic acid with an amino group attached to the 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.
Connection of amino acids in peptides and proteins
Amino acids are linked into dimers, trimers and polymers through a peptide bond. It is formed by cleavage of a hydroxyl (-OH) group from the carboxyl site of one alpha-amino acid and hydrogen (-H) from the amino group of another alpha-amino acid. As a result of the interaction, water is split off, and a C=O site with a free electron near the carbon of the carboxyl residue remains at the carboxyl end. In the amino group of another acid, there is a residue (NH) with an existing free radical at the nitrogen atom. This allows two radicals to be connected to form a bond (CONH). It's called peptide.
Alpha amino acid variants
There are 23 known alpha-amino acids. They arelisted as: glycine, valine, alanine, isolecine, leucine, glutamate, aspartate, 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 nonessential and nonessential.
The concept of nonessential and essential amino acids
Replaceables can be synthesized by the human body, while essentials must come only from food. At the same time, both essential and non-essential acids are important for protein biosynthesis, because without them the synthesis cannot be completed. Without one amino acid, even if all the others are present, it is impossible to build exactly the protein that the cell needs to perform its functions.
One mistake at any of the stages of biosynthesis - and the protein is no longer suitable, because it will not be able to assemble into the desired structure due to a violation of electronic densities and interatomic interactions. Therefore, it is important for a person (and other organisms) to consume protein foods that contain essential amino acids. Their absence in food leads to a number of protein metabolism disorders.
The process of forming a peptide bond
The only monomers of proteins are alpha-amino acids. They gradually combine into a polypeptide chain, the structure of which is pre-stored in the genetic code of DNA (or RNA, if bacterial biosynthesis is considered). A protein is a strict sequence of amino acid residues. This is a chain ordered in a certaina structure that performs a pre-programmed function in a cell.
Step sequence of protein biosynthesis
The process of protein formation consists of a chain of steps: replication of a DNA (or RNA) section, synthesis of information type RNA, its release into the cytoplasm of the cell from the nucleus, connection with the ribosome and gradual attachment of amino acid residues that are supplied by transfer RNA. A substance that is a protein monomer participates in the enzymatic reaction of the elimination of a hydroxyl group and a hydrogen proton, and then joins the growing polypeptide chain.
Thus, a polypeptide chain is obtained, which, already in the cellular endoplasmic reticulum, is ordered into some predetermined structure and supplemented with a carbohydrate or lipid residue, if required. This is called the process of "maturing" the protein, after which it is sent by the transport cellular system to its destination.
Functions of synthesized proteins
Protein monomers are the amino acids needed to build their primary structure. The secondary, tertiary and quaternary structure is already formed by itself, although sometimes it also requires the participation of enzymes and other substances. However, they are no longer essential, although they are essential for proteins to perform their function.
Amino acid, which is a protein monomer, 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 insertion groups. This allows you to create fromprotein derivative that plays the role of an enzyme, receptor, carrier of substances into or out of a cell, immunoglobulin, structural component of a membrane or cell organelle, muscle protein.
Proteins, formed from amino acids, are the only basis of life. And today it is believed that life just arose after the appearance of the amino acid and as a result of its polymerization. After all, it is the intermolecular interaction of proteins that is the beginning of life, including intelligent life. All other biochemical processes, including energy ones, are necessary for the implementation of protein biosynthesis, and as a result, the further continuation of life.
