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This week on TestTube Plus, host Trace Dominguez talks about viruses. In the first episode, he discussed times that viruses almost destroyed humanity. In future episodes of this series, he'll be contemplating if we should be scared of unknown viruses, how scientists are hacking viruses to help us live longer, and in the final episode, he will be asking: is humanity a virus? In today's show, he's analyzing whether or not viruses can technically be considered alive, and--if not--then what are they?
The first virus ever discovered was the tobacco mosaic virus by Russian scientist Dmitri Ivanovsky and Dutch microbiologist Martinus Beijerinck at the end of the 19th century. Although they didn't fully understand what it was they had discovered, it was clear this tobacco disease was being caused by a pathogen significantly smaller than a bacterium. Beijerinck named it a virus, which etymologically relates to poison. Viruses are sometimes described as "biological chemicals": they exist in a grey area between life and complex organic molecules. A virus has either DNA or RNA protected by a lipid membrane called a capsid. They are microscopic, usually measuring between 17 to 300 nanometers long.
Viruses don't contain the enzymes needed for chemical reactions (like replication, for example). They need a host cell (plant, animal, bacteria, etc) to multiply: once they infiltrate a cell, they start forcing it to replicate its own genes. The host cell becomes filled with newly created viruses until it literally explodes open, releasing a whole new batch of viruses which then attach to other cells, thus continuing the cycle. This is how and why viruses can spread so fast.
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Discovery of the first virus, the tobacco mosaic virus (NIH.gov)
"Two scientists contributed to the discovery of the first virus, Tobacco mosaic virus. Ivanoski reported in 1892 that extracts from infected leaves were still infectious after filtration through a Chamberland filter-candle. "
Are Viruses Alive? (Scientific American)
"Although viruses challenge our concept of what "living" means, they are vital members of the web of life"
General Properties of Viruses (ATSU.edu)
"Viruses contain either DNA or RNA as their genetic material, but not both. This nucleic acid usually has unique chemical and/or physical features which makes it distinguishable from human nucleic acid."