How does protein biosynthesis work?

The biosynthesis of the protein occurs in all organs, tissues and cells. The greatest amount of protein is synthesized in the liver. Ribosomes carry out protein biosynthesis. According to the chemical nature of the ribosome, 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 of 3 to 100 units - a 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.

Protein biosynthesis (second stage) is the interaction and connection of the activated amino acid with tRNA. The 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 a carboxyl group from the hydroxyl of the second Carbon atom to the ribose ribbon of the tRNA nucleotide.

Protein biosynthesis (the third stage) is the transportation of a complex of activated amino acid with t-RNA into the cell's ribosomes. 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 t-RNAs (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 i-RNA-ribosome complex. 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. During the 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 the initiation of the polypeptide 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.

Termination of the polypeptide chain. Ribosome, on the surface of which the polypeptide chain was synthesized, reaches the end of the i-RNA chain, 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 molecule of the polypeptide. 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 tRNA.

In the hyaloplasm, simple and complex proteins are formed from polypeptide chains . Secondary, tertiary and, in many cases, quaternary structures of the protein molecule are formed. Thus, protein biosynthesis takes place in the cell.