| Sections on virus infection |
| Discovery of virus |
Virus was formally recognized as microscopic bacteria. When German scientist Adolf Mayer attempted to determine the cause of tobacco mosaic disease in 1883, he observed that the disease could be transmitted to other plants by spraying sap from infected leaves. He later claimed that the disease was caused by small bacteria that could not be seen under the microscope.
A decade after Mayer's finding, Dimitri Ivanowsky sought to remove the pathogenic bacteria by using the filter. The disease, however, continued to infect plants in vicinity. Ivanowsky's demonstration confirmed the existence of a living form smaller than bacteria. Furthermore, Martinus Beijernick in 1897 showed that the agent of the disease was able to reproduce despite the filtering. Finally, Wendell Stanley proved the existence of virus when he successfully crystallized the infectious particle.
Top| General structure of virus |
Genome: Viruses may have different types of genes to propagate themselves. Viral genomes include double-stranded DNA, singled-stranded DNA, double-stranded RNA, and singled-stranded RNA.
Protective proteins: Viruses may have a protective protein shell,
capsid, and a membranous envelope. Some viruses contain few functional
enzymes in their capsids.
Different types of viruses have different shape of the capsid. Diagram
on the left, for instance, is an example of the adenovirus capsid.
Glycoprotein: Glycoprotein is a protein bonded to a chain of carbohydrates. It may function as a tool used for cell-to-cell recognition.
Top| Classification of virus |
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Virus classification
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Description
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Diseases
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Hepatovirus
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Uses single-stranded RNA as mRNA
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Poxvirus
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Uses double-stranded DNA for replication
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Smallpox, vaccinia
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Filovirus
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Uses single-stranded RNA for replication
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Ebola, marburg
virus
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Retrovirus
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Uses single-stranded RNA for reverse transcription
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AIDS, HIV, leukemia
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Coronavirus
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Uses single-stranded RNA for replication
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| Viral reproductive cycle (DNA-based) |
A virus enters a host cell and injects its DNA strands and capsids into the cell. The virus uses the host cell's DNA polymerase to replicate its viral DNA strands. On the other hand, the virual DNA produces capsids via RNA transcription and translation. After assembly of vital parts, the newly formed DNA and capsids fuse to form a new virus.
Top| Viral reproductive cycle (RNA-based) |
A virus enters a host cell and injects its RNA strand and capsids into the cell. The virus uses the host cell's resources to generate a new RNA by replicating a template RNA. mRNA generates new capsids through RNA translation. Newly formed RNAs and capsids fuse together to form a new RNA virus.
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