Life is a process of the existence of proteinmolecules. This is how many scientists express it, who are convinced that protein is the basis of all life. These judgments are absolutely correct, because the given substances in the cell have the largest number of basic functions. All other organic compounds play the role of energy substrates, and energy is again needed to synthesize protein molecules.
The ability of the body to synthesize protein
Not all existing organisms are capable ofto carry out the synthesis of proteins in the cell. Viruses and certain types of bacteria can not form proteins, and therefore are parasites and receive the necessary substances from the host cell. The remaining organisms, including prokaryotic cells, are capable of synthesizing proteins. All human cells, animals, plants, fungi, almost all bacteria and protists live at the expense of the ability of protein biosynthesis. This is required for the realization of the structure-forming, protective, receptor, transport and other functions.
Stage characteristic of protein biosynthesis
The structure of the protein is encoded in the nucleic acidacid (DNA or RNA) in the form of codons. This is hereditary information, which is reproduced every time a cell needs a new protein substance. The beginning of biosynthesis is the transfer of information into the nucleus about the need to synthesize a new protein with already prescribed properties.
In response, the area is despiralizednucleic acid, where its structure is encoded. This site is duplicated by the information RNA and transferred to the ribosomes. They are responsible for constructing a polypeptide chain based on the matrix - information RNA. Briefly all the stages of biosynthesis are presented as follows:
- transcription (the stage of doubling the DNA portion with the encoded protein structure);
- processing (the stage of formation of information RNA);
- translation (synthesis of proteins in a cell based on information RNA);
- posttranslational modification ("maturation" of the polypeptide, formation of its volume structure).
Nucleic acid transcription
The entire synthesis of proteins in the cell is carried outribosomes, and information about molecules is contained in the nucleic acid (RNA or DNA). It is located in the genes: each gene is a certain protein. The genes contain information about the amino acid sequence of the new protein. In the case of DNA, the removal of the genetic code is carried out in this way:
- the release of the nucleic acid from histones begins, despiralization occurs;
- DNA polymerase doubles the portion of DNA in which the protein gene is stored;
- The doubled site is the precursor of the information RNA, which is processed by enzymes to remove non-coding inserts (it is based on the synthesis of mRNA).
On the basis of the information RNA, the synthesis of mRNA occurs. It is already a matrix, after which the synthesis of proteins in the cell occurs on the ribosomes (in the rough endoplasmic reticulum).
Ribosomal synthesis of protein
Information RNA has two ends thatare made out as 3`- 5`. The reading and synthesis of proteins on the ribosomes begins at the 5 'end and continues to the intron - a site that does not encode any of the amino acids. This happens as follows:
- the information RNA "strands" on the ribosome, joins the first amino acid;
- The ribosome is displaced by the information RNA into one codon;
- transport RNA provides the desired (encoded by the given codon of mRNA) alpha-amino acid;
- the amino acid is attached to the starting amino acid to form a dipeptide;
- then the mRNA is again shifted to one codon, an alpha-amino acid is brought in and attached to the growing peptide chain.
Once the ribosome reaches the intron(non-coding insert), the information RNA simply moves on. Then, as the information RNA moves, the ribosome again reaches the exon - a region whose nucleotide sequence corresponds to a specific amino acid.
From this place, the joining begins againmonomers of the protein to the chain. The process continues until the appearance of the next intron or to the stop codon. The latter stops the synthesis of the polypeptide chain, after which the primary structure of the protein is considered complete and the stage of post-synthetic (post-translational) modification of the molecule begins.
After translation, the synthesis of proteins occurs incisterns of a smooth endoplasmic reticulum. The latter contains a small amount of ribosomes. In some cells, they may not be present in the RES at all. Such areas are necessary for the formation of a secondary, then a tertiary or, if it is programmed, a quaternary structure.
The entire synthesis of proteins in the cell occurs with the costa huge amount of ATP energy. Therefore, all other biological processes are needed to maintain protein biosynthesis. In addition, some of the energy is needed to transport proteins in the cell by active transport.
Many of the proteins are transferred from one locationcells to another for modification. In particular, post-translational synthesis of proteins occurs in the Golgi complex, where a carbohydrate or lipid domain is attached to a polypeptide of a specific structure.