An adenovirus is so small that 10 million of them would fit on this full stop. This type of virus causes colds and flu. It has an...Read More >>An adenovirus is so small that 10 million of them would fit on this full stop. This type of virus causes colds and flu. It has an outer protein shell made of triangular sections. The smallest living things are viruses. They are “alive” only because they can produce more of their kind if they invade another living thing. Viruses cannot reproduce on their own. They get into another living cell, the host cell, and take over its life processes to make more copies of themselves. In the process they destroy the host cell. A typical virus has an outer shell or coat made of proteins. Inside is a length of genetic material, usually DNA. They are incredibly tiny: the smallest viruses to be studied are 20 billionths of a metre in diameter. Most viruses are too small even to be observed through an optical microscope, and can only be viewed through electron microscopes.
Bacteriophages, often known as "phages", are large viruses that attack bacteria. They consist of a head or capsid containing a...Read More >>Bacteriophages, often known as "phages", are large viruses that attack bacteria. They consist of a head or capsid containing a length of genetic material, a rod-like body contained in a sheath and a set of six slender tail fibres that anchor the phage to its host.
Kinds of virus
Different viruses are shaped like bricks, rods, golf balls and even space rockets. Many can exist in their non-living form for years and be frozen solid, boiled or made into crystals—yet still come alive when host cells are available.
Viruses cause diseases in plants, animals and people. These include colds, flu, measles and AIDS (caused by the Human Immunodeficiency Virus, HIV).
A simian virus, SV40, capable of causing tumours in both monkeys and humans.
Viruses were first discovered in the 1890s.
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