Since viruses do not belong to the cellular form of life, the term "virion" is used as a designation for a discrete viral particle. This concept was introduced in 1962 by the Frenchman André Lvov.
The virus does not exist in this form all the time, but only at a certain stage of its life cycle.
What is a virion
Virion is the final phase of the development of the virus, which includes a complete set of structural and functional elements packed into a single particle. This form is typical for the extracellular stage of the life cycle of the virus, however, for some time after assembly, the virion can also exist inside the infected cell.
Since the virion is just a designation of a morphological unit, it should not be identified with the concept of "virus". The latter includes the entire set of biological properties that characterize this taxon, and not just structural features.
The structure of the virion
A virus particle consists of a nucleic acid (RNA or DNA) surrounded by a protein layer (capsid) that performs protective functions andprovides interaction with the host cell. Some virions have an additional shell in the form of a bilipid membrane pierced by spikes of virus proteins sticking out. This structure is of cellular origin and is called the supercapsid. Viral particle sizes range from 20 to 200 nm.
Protein subunits of the virion envelope can be folded into various spatial configurations, on the basis of which the morphological classification of viruses is built. According to the type of structural organization, virions are distinguished:
- with helical symmetry - protein units are arranged in a spiral, in the center of which lies a similarly structured nucleic acid;
- with cubic symmetry - equilateral triangles (capsomeres) formed from protein molecules form various forms of polyhedra (tetrahedra, octahedrons, icosahedrons, etc.);
- with binary (mixed) symmetry - combination of both types of organization in one viral particle (typical for bacteriophages);
- intricately organized, covered with supercapsid.
In addition to the structural envelope subunits, some virions contain enzymes necessary for the transcription of genetic material.
The spatial structure, protein composition and type of nucleic acid of the virion are the main taxonomic features of the biological differentiation of viruses. Additional criteria are life history features and host spectrum.
Genetic material of virus particles
Unlike the genetic material of other organisms, the virions of viruses contain only one type of nucleic acid: DNA or RNA. These molecules can be circular or linear, fragmented or whole, with closed (completely or partially) or free ends, contain both two chains and one. Such a variety of organization of nucleic acids is characteristic only for viruses.
The viral genome also has a functional characteristic. So, virion RNA can be positive, that is, it can be translated in the host cell with the formation of viral proteins, and negative, not possessing template activity (in this case, translation is preceded by the synthesis of positive RNA by an enzyme that is part of the virus - transcriptase).
Depending on the combination of these characteristics, virions are divided into 6 types of RNA:
- single-stranded unfragmented positive;
- single-stranded unfragmented negative;
- single strand fragmented negative;
- double-strand fragmented negative;
- single strand double positive;
- single-stranded circular defective.
In the DNA genome, "+" and "-" chains are distinguished and the following types of molecular organization are distinguished:
- partially single-stranded circular;
- superspiral closed ring;
- single strand linear;
- linear duplex;
- linear duplex with covalently crosslinked ends;
- single strandedlinear;
Among all types of genomes, groups are distinguished, each of which is characterized by a certain mechanism of replication in an infected cell.
Assembly of the virion inside the host cell
The formation of viral particles is carried out by enzymes and biosynthesis mechanisms of the infected cell, which the virus forces to work for itself. This process includes several steps.
First, the virion's genetic material enters the host cell. At the same time, in simple viruses, the protein shell remains outside, while in complex viruses it penetrates inside due to the fusion of the supercapsid with the plasma membrane (receptor endocytosis). In the latter case, the capsid found in the cytoplasm is destroyed by the action of the lytic enzymes of the phagosome.
On the basis of nucleic acid, 2 processes proceed in parallel: genome replication (creation of many copies of DNA or RNA genetic molecules) and translation of virion proteins in the ribosomal apparatus of the host cell.
Synthesized protein and genetic elements are combined into a nucleocapsid - a full-fledged virion of simple viruses. In complex, assembly is completed at the moment the particle leaves the cell, during which the capsid is enveloped by a plasma membrane containing receptor proteins pre-built into it.
Scientific and Production Association "Virion"
Research enterprise "Virion" is the largest pharmaceutical complex for the creation and production of immunobiologicaldrugs price Russia. In 1906, it was founded as the Tomsk Bacteriological Institute named after Ivan and Zinaida Churin, and in 1953 it received the status of the Research Institute of Vaccines and Serums. In 1988, the Institute was renamed into Scientific and Production Association (NPO) "Virion", which later became a branch of the Moscow Federal State Unitary Enterprise NPO "Microgen".
The main activities of the company include the creation and production of immunoglobulins, antiviral vaccines, probiotics, psychotropic drugs and various drugs for diagnostics. The company is located at Tomsk, Ivanovsky street 8.
At present, the Virion production complex is a well-known large company with a high-tech production base and a professional staff of 600 people.
