The biosynthesis of protein occurs in all organs,tissues and cells. The greatest amount of protein is synthesized in the liver. Ribosomes carry out protein biosynthesis. The chemical nature of the ribosome is nucleoproteins consisting of RNA (50-65%) and proteins (35-50%). Ribonucleic acid is an integral part of the granular endoplasmic reticulum, where biosynthesis and movement of synthesized protein molecules occurs.
Ribosomes in the cell are in the form of clusters from 3 to 100 units - polis (polyribosome). Ribosomes are usually interconnected by a kind of filament visible under the electron microscope - i-RNA.
Each ribosome is capable of synthesizing a single polypeptide chain independently, a group of several such chains and protein molecules.
Stages of protein biosynthesis
Activation of amino acids.Amino acids enter the hyaloplasm from the intercellular fluid as a result of diffusion, osmosis or active transfer. Each species of amino- and imino acids interacts with an individual enzyme-aminoacyl synthetase. The reaction is activated by cations of magnesium, manganese, cobalt. There is an activated amino acid.
Biosynthesis of protein (second stage) - interaction andthe connection of an activated amino acid with tRNA. Activated amino acids (aminoacyladenylate) are transferred by enzymes to the cytoplasm tRNA. The process is catalyzed by aminoacyl-RNA synthetases. The amino acid residue is connected by the carboxyl group from the hydroxyl of the second Carbon atom to the ribose ribbon of the tRNA nucleotide.
Biosynthesis of protein (the third stage) - transportationcomplex activated amino acid with t-RNA in the ribosome cells. The amino acid is associated with t-RNA, transferred from the hyaloplasm to the ribosome. The process is catalyzed by specific enzymes that are at least 20 in the body. Some amino acids are transported by several tRNAs (eg, valine and leucine - three tRNAs). In this process, the energy of GTP and ATP is used. The fourth stage of biosynthesis is characterized by the binding of aminoacyl-t-RNA to the complex of the i-RNA-ribosome. Aminoacyl-t-RNA, coming to the ribosome, interacts with i-RNA. Each t-RNA has a site consisting of three nucleotides - an anticodon. In the i-RNA it corresponds to a region with three nucleotides - the codon. Each codon corresponds to the anticodon t-RNA and one amino acid. In the course of biosynthesis, the ribosomes are joined in the form of aminoacyl-tRNA amino acids, which are subsequently formed in the polypeptide chain in the order determined by the placement of codons in the i-RNA.
The next stage of protein biosynthesis is initiationpolypeptide chain. After two adjacent aminoacyl-t-RNA with their anticodons joined the codons of i-RNA, conditions are created for the synthesis of the polypeptide chain. A peptide bond is formed. These processes are catalysed by peptidesyntases, activated by Mg cations and protein initiation factors F1, F2, F3. The source of chemical energy is guanosine triphosphate acid.
Терминация полипептидной цепи.Ribosome, on the surface of which the polypeptide chain was synthesized, reaches the end of the i-RNA chain, and subsequently "jumps" out of it. To the opposite end of the i-RNA, a new ribosome joins its place, which carries out the synthesis of the next polypeptide molecule. The polypeptide chain disconnects from the ribosome and is released into the hyaloplasm. This reaction is carried out using a specific release factor (factor R), which is connected to the ribosome and facilitates the hydrolysis of the ester bond between the polypeptide and t-RNA.
In hyaloplasm polypeptide chains are formedsimple and complex proteins. Secondary, tertiary, and in many cases, quaternary structures of the protein molecule are formed. Thus, protein biosynthesis occurs in the cell.
