Protein is the basis of cell and body life. Performing a huge number of functions in living tissues, it implements its main capabilities: growth, vital activity, movement and reproduction. In this case, the cell itself synthesizes a protein, the monomer of which is an amino acid. Its position in the primary structure of the protein is programmed by the genetic code, which is inherited. Even the transfer of genes from a mother cell to a daughter cell is only an example of the transfer of information about the structure of a protein. This makes it a molecule that is the foundation of biological life.
General characteristics of protein structure
Protein molecules synthesized in a cell are biological polymers.
In a protein, the monomer is always an amino acid, and their combination makes up the primary chain of the molecule. It is called the primary structure of a protein molecule, which later spontaneously or under the action of biological catalysts is modified into a secondary, tertiary or domain structure.
Secondary and tertiary structure
Secondary proteinstructure is a spatial modification of the primary chain associated with the formation of hydrogen bonds in polar regions. For this reason, the chain is folded into loops or twisted into a spiral, which takes up less space. At this time, the local charge of the sections of the molecule changes, which triggers the formation of a tertiary structure - a globular one. The crimped or helical sections are twisted into balls with the help of disulfide bonds.
The balls themselves allow you to form a special structure that is needed to perform the programmed functions. It is important that even after such a modification, the monomer of the protein is an amino acid. This also confirms that during the formation of the secondary, and then the tertiary and quaternary structure of the protein, the primary amino acid sequence does not change.
Characterization of protein monomers
All proteins are polymers, the monomers of which are amino acids. These are organic compounds that are either synthesized by a living cell or enter it as nutrients. Of these, a protein molecule is synthesized on the ribosomes using the messenger RNA matrix with a huge expenditure of energy. Amino acids themselves are compounds with two active chemical groups: a carboxyl radical and an amino group located at the alpha carbon atom. It is this structure that allows the molecule to be called an alpha-amino acid, capable of forming peptide bonds. Protein monomers are only alpha-amino acids.
Peptide bond formation
A peptide bond is a molecular chemical group formed by carbon, oxygen, hydrogen and nitrogen atoms. It is formed in the process of splitting off water from the carboxyl group of one alpha-amino acid and the amino group of another. In this case, the hydroxyl radical is split off from the carboxyl radical, which, combining with the proton of the amino group, forms water. As a result, two amino acids are connected by a covalent polar bond CONH.
Only alpha-amino acids, monomers of proteins of living organisms, can form it. It is possible to observe the formation of a peptide bond in the laboratory, although it is difficult to selectively synthesize a small molecule in solution. Protein monomers are amino acids, and its structure is programmed by the genetic code. Therefore, amino acids must be connected in a strictly designated order. In a solution under chaotic equilibrium conditions, this is impossible, and therefore it is still impossible to synthesize a complex protein artificially. If there is equipment that allows a strict order of assembly of the molecule, its maintenance will be quite expensive.
Protein synthesis in a living cell
In a living cell, the situation is reversed, since it has a developed biosynthesis apparatus. Here, the monomers of protein molecules can be assembled into molecules in a strict sequence. It is programmed by the genetic code stored in the chromosomes. If it is necessary to synthesize a certain structural protein or enzyme, the process of reading the DNA code and forming a matrix (andRNA) from which protein is synthesized. The monomer will gradually join the growing polypeptide chain on the ribosomal apparatus. Upon completion of this process, a chain of amino acid residues will be created, which spontaneously or during the enzymatic process will form a secondary, tertiary or domain structure.
Regularities of biosynthesis
Some features of protein biosynthesis, transmission of hereditary information and its implementation should be highlighted. They lie in the fact that DNA and RNA are homogeneous substances consisting of similar monomers. Namely, DNA is made up of nucleotides, just like RNA. The latter is presented in the form of informational, transport and ribosomal RNA. This means that the entire cellular apparatus responsible for storing hereditary information and protein biosynthesis is a single whole. Therefore, the cell nucleus with ribosomes, which are also domain RNA molecules, should be considered as one whole apparatus for storing genes and their implementation.
The second feature of the biosynthesis of a protein, the monomer of which is an alpha-amino acid, is to determine the strict order of their attachment. Each amino acid must take its place in the primary protein structure. This is ensured by the apparatus described above for the storage and implementation of hereditary information. Errors may occur in it, but they will be eliminated by it. In case of incorrect assembly, the molecule will be destroyed, and biosynthesis will start again.
