Virus Discovery Composition Structure Names Viral Reproduction

Virus Composition Structure Naming and Viral Reproduction

Viruses are a class of microorganisms that do not have cell structures and are intertwined with life features such as genetics and replication. They are non-cellular microbial groups. It has the characteristics of life in the host cell, only the characteristics of general chemical macromolecules outside the living cell, and obligate parasitization in the living cell. Individuals are tiny and can be seen under an electron microscope through a bacterial filter. The size is expressed in nanometers (nm). In 1892, the Russian scholar Ivanovsky first discovered that the pathogen of tobacco mosaic disease could pass unimpeded through the porcelain that bacteria could not pass through, so it was named filter virus or virus. Viruses are small and have no cell structure. Most of them can be observed with an electron microscope. Various viruses have different structures and morphologies, and have strict host specificity, that is, they can only proliferate in certain types of living cells. 

The basic chemical composition of viruses is nucleic acids and egg protein. Some viruses also contain lipids, polysaccharides and inorganic salts. A virus has only one type of nucleic acid (DNA or RNA) genetic material. Depending on the host, viruses can be divided into animal viruses, plant viruses and bacterial viruses (phages).

Table of Content

  1.    Virus Discovery

  2.    Chemical composition of the virus

  3.    Structure of the virus

  4.    Viral Reproduction

  5.    Classification and naming of viruses

How virus was discovered?

Although early on, people recognized the presence of the virus through disease caused by the virus. In the second and third centuries BC, India and China had records of smallpox. However, the discovery and identification of viruses was a matter of the late 19th century.

In 1886, Mayer, a German working in the Netherlands, was attracted by a pathological condition of tobacco. His symptoms were infection of dark, shallow green areas on the leaves. The leaves of the plant are crushed with water, and the juice is injected into the veins of healthy tobacco, which can cause mosaic disease, which proves that the disease is contagious. Through analysis of leaves and soil, Maier pointed out that tobacco mosaic is caused by bacteria.

Mayr's Experiment for Viruses

In 1892, Russian biologist Ivanovski repeated Mayr's experiments, confirming the phenomenon Mayr saw, and further found that the leaf juice of diseased tobacco plants passed through a bacterial filter It can also cause mosaic disease in healthy tobacco plants. This phenomenon can at least explain that the pathogenic cause is not bacteria, but Ivanovsky explained that it was caused by toxins produced by bacteria. Living in the heyday of Pasteur's theory of bacterial pathogenicity, Ivanovsky was unable to think further, thus missing a major discovery.

In 1898, the Dutch bacteriologist Beijerinck also confirmed Maier's observations, and, like Ivanovsky, found that the tobacco mosaic pathogen could pass through bacterial filters, but Bergerinck Think deeper. He placed the sap of the tobacco mosaic virus strain on the surface of the agar gel block and found that the substance infected with tobacco mosaic disease diffused at a moderate rate in the gel, while the bacteria remained on the surface of the agar.

Soluble live bacteria

 Since Bejlink's experiments did not show the particle morphology of the pathogen, he called it contagium vivum fluidum (soluble live bacteria), named the virus, and called it Virus in Latin. No doubt Bejlink became the discoverer of the virus. However, Bergerinck believed that the virus exists in liquid form, but this view was later overturned by American biochemist and virologist Stanley, who proved that the virus is granular. Virus size and morphology

Virus sizes vary widely by species. Small viruses are only 10 to 22 nanometers, such as foot-and-mouth disease virus, which is equivalent to the largest protein molecule (heme protein molecule); large viruses, such as pox virus, are 250-300 × 200-250 nanometers in size, which is approximately the smallest prokaryotic Mycoplasma microorganisms.

Most plant viruses range in length from 300 nanometers (such as tobacco mosaic virus) to 750 nanometers (such as potato Y virus) and are about 10-20 nanometers wide. The morphology of the virus varies by species. Animal viruses are generally spherical, oval. or brick-shaped. Plant viruses are mainly rod-shaped or filamentous, and many are spherical. Bacterial viruses are mostly tadpole-shaped and also micro-spherical and filamentous.

Chemical composition of virus

The chemical composition of most viruses is nucleic acids and proteins, and some also contain lipids and polysaccharides.

Viral nucleic acid A virus contains only one type of nucleic acid (RNA or DNA). Most plant viruses contain RNA and a few contain DNA; phages mostly contain DNA and a few contain RNA, such as E. coli phages M13 and M12; some animal viruses contain DNA, such as variola virus, and some contain RNA, such as influenza virus. In biological cells, DNA is double-stranded and RNA is single-stranded, but the situation is more complicated in viruses. Nucleic acid content varies greatly among different viruses, some are only 1%, such as influenza viruses, and some are as high as 50%, such as E. coli T-line even phage.

The protein of the virus mainly constitutes the shell of the virus particle and protects the virus nucleic acid from being destroyed by nucleases and other physical and chemical factors; determines the specificity of the virus infection and has specific affinity with the receptors present on the surface of susceptible cells; determines the antigenicity of the virus ; Stimulate the body to produce corresponding antibodies. Viral proteins also constitute enzymes in the virus.

Other ingredients The lipids and polysaccharides are contained in the coatings of more complex viruses (such as pox virus). Lipids account for 50 to 60% of the lipids and the rest is cholesterol. Polysaccharides often exist in the form of glycolipids and glycoproteins.

Structure of virus

The structure is intact and infectious individuals are called virions. The nucleocapsid is the basic structure of virions. Complex viruses have a capsule on the outer surface of the nucleocapsid, and there are spikes on it. Because the capsid particles are arranged and combined in different ways, the virus assumes different configurations and shapes.

Viral reproduction

Replication (replication) is a way for viruses to multiply. The entire process is called the replication cycle and includes five consecutive steps: adsorption, invasion, husking, biosynthesis, assembly and release. The virus lacks the enzyme system and energy necessary for metabolism and the raw materials, energy and biosynthetic site required for its proliferation are provided by the host cells. Under the control of viral nucleic acid, the virus's nucleic acid (RNA or DNA) and protein are synthesized, and then assembled into mature, infectious viral particles in the cytoplasm or nucleus of the host cell and then released to the cell in various ways External infection of other cells.

Classification and naming of viruses

Names of Viruses: According to the International Virus Classification Commission's principles for virus classification and naming, its classification basis includes the host of the virus, the disease it causes, the shape and size of the virus particle, the type, structure, and chain number of the nucleic acid, and the presence or absence of the capsule of the virus particle. Among them, virus nucleic acid is DNA or RNA, the virus genome is a single component or multiple groups of systems, and the presence or absence of capsular vesicles is the three important characteristics of the virus. The viruses currently understood are divided into seven categories, with 59 families (groups). Or groups), in practice, viruses are still divided into plant viruses, animal viruses (also divided into vertebrate viruses, insect viruses) and microbial viruses (also divided into phages and fungi) according to the host.

Viruses are not only the research objects of microbiology and virology, but also the important research objects of molecular biology and molecular genetics. As the pathogen of many diseases, the research on virus diseases and its prevention has important practical significance.

Viruses invade animals, plants and microorganisms, destroy animal husbandry and crops, and cause significant losses to the national economy. The virus is very harmful to human health, and many infectious diseases such as influenza, measles, Japanese encephalitis, pneumonia, and polio are all caused by the virus. Certain viruses can also cause tumors in animals. Bacterial virus pollution is a taboo in the fermentation industry, threatening the fermentation production of pesticides, antibiotics, enzyme preparations, organic solvents and dairy production. Some viruses can be used to control pests and pathogens. Viruses are also important experimental materials for molecular biology research.

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