Virus
Say it: VY-rus
A virus is a tiny infectious particle of DNA or RNA inside a protein coat that can multiply only by taking over the machinery of a living host cell.
Also: viruses, virion, viral particle
Definition
What is a virus?
A virus is an infectious agent much smaller than a bacterium, made of genetic material, either DNA or RNA but never both, packed inside a protein shell called a capsid. Some viruses also have an outer envelope, a piece of host cell membrane carrying viral proteins, which they pick up as they leave a cell. A complete virus particle outside a cell is called a virion.
Viruses are not made of cells, have no metabolism of their own and cannot reproduce independently, so they are obligate intracellular parasites. A virus attaches to specific receptors on a host cell, delivers its genome inside, and uses the cell's ribosomes, enzymes and energy to make new viral parts. These assemble into new virions, which leave by bursting the cell or budding from it. Each virus usually infects only certain species and cell types, its host range. Viruses infect all kinds of organisms, and those that infect bacteria, the bacteriophages, are the most abundant.
Most virions measure tens to hundreds of nanometers, too small to see with a light microscope. Viral diseases of humans include influenza, measles, AIDS and COVID-19. Antibiotics have no effect on viruses, so viral infections are prevented with vaccines, and some are treated with antiviral drugs.
Word parts
Where does the word “virus” come from?
- virus
- poison, venom, slimy liquidLatin virus
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Related
Terms that go with it
- CapsidA capsid is the protein shell of a virus that surrounds and protects its genome, built from many repeating protein subunits called capsomeres.
- BacteriophageA bacteriophage, or phage, is a virus that infects bacteria, injecting its genome and using the host cell's machinery to make new phages.
- RetrovirusA retrovirus is an RNA virus that copies its genome into DNA with reverse transcriptase and inserts that DNA into the host cell's chromosomes.
- Lytic cycleThe lytic cycle is a viral life cycle in which a phage takes over a bacterial cell, makes many copies of itself, then bursts the cell to release them.
- VaccineA vaccine is a preparation that trains the immune system to recognize a pathogen, so the body can fight it off quickly if it meets the real thing later.
- PathogenA pathogen is a microbe or other agent, such as a virus, bacterium, fungus, parasite or prion, that can cause disease in a host.
Sources
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