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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