Life is a process of existence of protein molecules. This is how many scientists express it, who are convinced that protein is the basis of all living things. These judgments are absolutely correct, because these 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 for the synthesis of protein molecules.
The body's ability to synthesize protein
Not all existing organisms are capable of synthesizing proteins in a cell. Viruses and some types of bacteria cannot form proteins, and therefore are parasites and receive the necessary substances from the host cell. Other organisms, including prokaryotic cells, are capable of synthesizing proteins. All human, animal, plant, fungal cells, almost all bacteria and protists live off the ability of protein biosynthesis. This is required for the implementation of structure-forming, protective, receptor, transport and other functions.
Stage responseprotein biosynthesis
The structure of a protein is encoded in nucleic acid (DNA or RNA) in the form of codons. This is hereditary information that is reproduced every time a cell needs a new protein substance. The beginning of biosynthesis is the transfer of information to the nucleus about the need to synthesize a new protein with already given properties.
In response to this, a section of nucleic acid is despiralized, where its structure is encoded. This place is duplicated by messenger RNA and transferred to ribosomes. They are responsible for building a polypeptide chain based on a matrix - messenger RNA. Briefly, all stages of biosynthesis are presented as follows:
- transcription (the stage of doubling the DNA segment with the encoded protein structure);
- processing (formation of messenger RNA);
- translation (protein synthesis in a cell based on messenger RNA);
- post-translational modification ("maturation" of the polypeptide, the formation of its three-dimensional structure).
Nucleic acid transcription
All protein synthesis in a cell is carried out by ribosomes, and information about molecules is contained in nucleic acid (RNA or DNA). It is located in the genes: each gene is a specific protein. Genes contain information about the amino acid sequence of a 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 site from histones begins, despiralization occurs;
- DNA polymerasedoubles the section of DNA that stores the protein gene;
- doubled section is a precursor of messenger RNA, which is processed by enzymes to remove non-coding inserts (mRNA synthesis is carried out on its basis).
Based on pro-information RNA, mRNA is synthesized. It is already a matrix, after which protein synthesis in the cell occurs on ribosomes (in the rough endoplasmic reticulum).
Ribosomal protein synthesis
Message RNA has two ends, which are arranged as 3`-5`. Reading and synthesis of proteins on ribosomes begins at the 5'end and continues to the intron, a region that does not encode any of the amino acids. It goes like this:
- messenger RNA "strings" onto the ribosome, attaches the first amino acid;
- the ribosome shifts along the messenger RNA by one codon;
- transfer RNA provides the desired (encoded by the given mRNA codon) alpha-amino acid;
- an amino acid joins the starting amino acid to form a dipeptide;
- then the mRNA is shifted one codon again, an alpha amino acid is brought in and joins the growing peptide chain.
Once the ribosome reaches the intron (non-coding insert), the messenger RNA just moves on. Then, as the messenger RNA advances, the ribosome again reaches the exon - the site whose nucleotide sequence corresponds to a certainamino acid.
From this point, the addition of protein monomers to the chain begins again. The process continues until the next intron appears or until 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 postsynthetic (post-translational) modification of the molecule begins.
Post-translational modification
After translation, protein synthesis occurs in the cisternae of the smooth endoplasmic reticulum. The latter contains a small number of ribosomes. In some cells, they may be completely absent in the RES. Such areas are needed to form first a secondary, then a tertiary or, if programmed, a quaternary structure.
All protein synthesis in the cell occurs with the expenditure of a huge amount of ATP energy. Therefore, all other biological processes are needed to maintain protein biosynthesis. In addition, some of the energy is needed for the transfer of proteins in the cell by active transport.
Many of the proteins are transferred from one location in the cell to another for modification. In particular, post-translational protein synthesis occurs in the Golgi complex, where a carbohydrate or lipid domain is attached to a polypeptide of a certain structure.
