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Viruses were expected to be small, but the range of sizes came as a surprise. Some were only a little smaller than the smallest known bacteria, and the smaller viruses were of similar sizes to complex organic molecules. [14] In 1935, Wendell Stanley examined the tobacco mosaic virus and found it was mostly made of protein. [15]
Viral evolution is a subfield of evolutionary biology and virology that is specifically concerned with the evolution of viruses. [1] [2] Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates (on the order of one point mutation or more per genome per round of replication).
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. [2] [3] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.
In 1935, American biochemist and virologist Wendell Meredith Stanley examined the tobacco mosaic virus (TMV) and found it to be mainly made from protein. [7] A short time later, this virus was shown to be made from protein and RNA. [8] Rosalind Franklin developed X-ray crystallographic pictures and determined the full structure of TMV in 1955. [9]
The nature of viruses remained unknown until the invention of the electron microscope in the 1930s, when the science of virology gained momentum. In the 20th century many diseases both old and new were found to be caused by viruses. There were epidemics of poliomyelitis that were only controlled following the development of a vaccine in the 1950s.
The viral eukaryogenesis hypothesis posits that eukaryotes are composed of three ancestral elements: a viral component that became the modern nucleus; a prokaryotic cell (an archaeon according to the eocyte hypothesis) which donated the cytoplasm and cell membrane of modern cells; and another prokaryotic cell (here bacterium) that, by endocytosis, became the modern mitochondrion or chloroplast.
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Gamma phage, an example of virus particles (visualised by electron microscopy) Virology is the scientific study of biological viruses.It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they ...