Life is the process of the existence of protein molecules. That is how many scientists who are convinced that protein is the basis of all living things express themselves about it. 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 the 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 able to synthesize proteins. All human, animal, plant, fungal cells, almost all bacteria and protists live due to the ability of protein biosynthesis. This is required for the implementation of structure-forming, protective, receptor, transport and other functions.
Phase Characterization of Protein Biosynthesis
The protein structure is encoded in nucleic acid (DNA or RNA) as 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 specified properties.
In response to this, the nucleic acid site 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 step of doubling a portion of DNA with an encoded protein structure);
- processing (the stage of formation of information RNA);
- translation (protein synthesis in a cell based on messenger RNA);
- post-translational modification ("maturation" of the polypeptide, the formation of its bulk structure).
Nucleic acid transcription
The whole protein synthesis in the cell is carried out by ribosomes, and information about the molecules is contained in nucleic acid (RNA or DNA). It is located in the genes: each gene is a specific 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 as follows:
- the release of the nucleic acid site from histones begins, despiralization occurs;
- DNA polymerase doubles the portion of DNA in which the protein gene is stored;
- the doubled region is the precursor of messenger RNA, which is processed by enzymes to remove non-coding inserts (mRNA synthesis is performed on its basis).
Based on proinformational RNA, mRNA synthesis 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 protein synthesis
Informational RNA has two ends, which are arranged as 3`- 5`. Reading and synthesis of proteins on the ribosomes begins at the 5th end and continues to the intron, a region that does not encode any of the amino acids. This happens as follows:
- messenger RNA "strung" onto the ribosome, attaches the first amino acid;
- the ribosome is shifted by one codon in messenger RNA;
- transport RNA provides the desired alpha-amino acid (encoded by a given mRNA codon);
- the amino acid joins the starting amino acid with the formation of a dipeptide;
- then the mRNA is again shifted by one codon, an alpha amino acid is introduced and attached to the growing chain of the peptide.
Once the ribosome reaches the intron (non-coding insertion), messenger RNA simply moves on. Then, as the messenger RNA advances, the ribosome reaches the exon again — the region whose nucleotide sequence corresponds to a specific amino acid.
From this point, the addition of protein monomers to the chain begins again. The process continues until the next intron appears or to the stop codon. The latter terminates 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 tanks of a smooth endoplasmic reticulum. The latter contains a small number of ribosomes. In some cells, they may not be present at all in RES. Such sites are necessary for the formation of a secondary, then tertiary, or, if programmed, quaternary structure.
All protein synthesis in the cell takes a huge amount of ATP energy. Therefore, all other biological processes are needed to maintain protein biosynthesis. In addition, some of the energy needed for the transfer of proteins in the cell by active transport.
Many of the proteins are transferred from one cell location 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.