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Synthesis of proteins in the cell, the sequence of biosynthetic processes. Synthesis of proteins on ribosomes.

Life is the process of the 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 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 able to carry out the synthesis of proteins in the cell. Viruses and some 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 protein structure is encoded in a 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 into the nucleus about the need to synthesize a new protein with already specified properties.

In response to this, the nucleic acid region despiralizes , where its structure is encoded. This place 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 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 volumetric structure).

Nucleic acid transcription

All the synthesis of proteins in the cell is carried out by ribosomes, 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 conducted 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 (on its basis, the synthesis of mRNA is conducted).

Based on the information RNA, the synthesis of mRNA occurs. It is already a matrix, after which the synthesis of proteins in the cell takes place on the ribosomes (in the rough endoplasmic reticulum).

Ribosomal synthesis of protein

Information RNA has two ends, which are formed 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, attaches the first amino acid;
  • The ribosome is shifted along 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 certain amino acid.

From this point, the addition of protein monomers to the chain begins again. 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.

Post-translational modification

After translation, the synthesis of proteins occurs in the tanks 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 needed to form a secondary, then a tertiary or, if programmed, quaternary structure.

The entire synthesis of proteins 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 to transport 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 specific structure.

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