Protein is the basis of cell and body life. Performing a huge number of functions in living tissues, he realizes 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 protein structure is programmed by inherited genetic code. Even the transfer of genes from the mother cell to the daughter cell is just an example of the transfer of protein structure information. This makes it the molecule that makes up the foundation of biological life.
General characteristics of protein structure
The protein molecules synthesized in the cell are biological polymers.
In a protein, the amino acid is always the monomer, and their combination constitutes the primary chain of the molecule. It is called the primary structure of the protein molecule, which later changes spontaneously or under the influence of biological catalysts into a secondary, tertiary or domain.
Secondary and tertiary structure
The secondary protein structure 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 molecular sites changes, because of which the process of formation of the tertiary structure - globular - starts. Curved or spiral sections are twisted into balls with 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 amino acid is the monomer in the protein. 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 whose monomers are amino acids. These are organic compounds that are either synthesized by a living cell, or enter into it as nutrients. Of these, a protein molecule is synthesized on ribosomes using a messenger RNA matrix with a huge expenditure of energy. The amino acids themselves are compounds with two active chemical groups: a carboxy radical and an amino group localized 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 during the removal of water from the carboxyl group of one alpha amino acid and the amino group of another. In this case, the hydroxyl radical is cleaved from the carboxyl radical, which, when combined with the proton of the amino group, forms water. As a result, two amino acids are joined by the covalent polar bond CONH.
Only alpha-amino acids, the monomers of the proteins of living organisms, can form it. The formation of a peptide bond can be observed in laboratory conditions, although it is difficult to selectively synthesize a small molecule in solution. The monomers of the protein are amino acids, and its structure is programmed with a 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 not yet possible to synthesize a complex protein artificially. If equipment appears that allows for strict assembly of the molecule, its maintenance will be quite expensive.
Protein Synthesis in a Living Cell
In a living cell, the situation is the opposite, since it has a developed biosynthesis apparatus. Here, the monomers of protein molecules can be assembled into molecules in strict sequence. It is programmed with the genetic code stored on the chromosomes. If necessary, the synthesis of a specific structural protein or enzyme starts the process of reading the DNA code and the formation of a matrix (and RNA), on the basis of which the protein is synthesized. The monomer will gradually attach to the growing polypeptide chain on the ribosomal apparatus. Upon completion of this process, a chain of amino acid residues will be created, which will spontaneously or during the enzymatic process form a secondary, tertiary or domain structure.
Patterns of biosynthesis
Some features of protein biosynthesis, transmission of hereditary information and its implementation should be highlighted. They consist in the fact that DNA and RNA are homogeneous substances consisting of similar monomers. Namely, DNA consists of nucleotides, like RNA. The latter is presented in the form of information, transport and ribosomal RNA. This means that the entire cellular apparatus responsible for the storage of 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 protein biosynthesis, the monomer of which is an alpha amino acid, is to determine the strict order of their addition. Each amino acid must take its place in the primary protein structure. The apparatus for storing and implementing hereditary information described above is engaged in this. Errors may occur in it, but they will be eliminated by himself. In case of improper assembly, the molecule will be destroyed, and biosynthesis will start again.