Virus

Article

October 19, 2021

Viruses (from the Latin virus, "poison" or "toxin") are small infectious agents, most with a diameter of 20-300 nm, although there are viruses (0.6–1.5 µm) that have a constituted genome. of one or more nucleic acid molecules (DNA or RNA), which are either single-stranded or double-stranded. Virus nucleic acids are usually coated with a protein coat made up of one or more proteins, which may also be coated with a complex envelope made up of a lipid bilayer. Viral particles are extremely small, submicroscopic structures. Most viruses have small sizes, which are beyond the resolution limits of optical microscopes, and it is common for their visualization to use electron microscopes. Viruses are simple structures, compared to cells, and are not considered organisms, as they do not have organelles or ribosomes, and do not have all the biochemical potential (enzymes) necessary to produce their own metabolic energy. They are considered obligatory intracellular parasites (a characteristic that prevents them from being considered living beings), as they depend on cells to multiply. Also, unlike living organisms, viruses are unable to grow in size and divide. From host cells, viruses obtain: amino acids and nucleotides; protein synthesis machinery (ribosomes) and metabolic energy (ATP). Outside the intracellular environment, viruses are inert. However, once inside the cell, the replication capacity of viruses is surprising: a single virus is capable of multiplying, in a few hours, thousands of new viruses. Viruses are capable of infecting living beings from all domains (Eukarya, Archaea and Bacteria). In this way, viruses represent the greatest biological diversity on the planet, being more diverse than bacteria, plants, fungi and animals combined. Nearly 200,000 different types of viruses spread in the world's oceans, according to one study. The 2019 count is 12 times higher than the previous census of marine viruses recorded in 2016. There are, individually, about ten nonillions (10³¹) of viruses on planet Earth, a number one hundred million times greater than the number of stars on Earth. observable universe.

History

In the mid-nineteenth century, Louis Pasteur proposed the microbial theory of disease, in which he explained that all diseases were caused and propagated by some “tiny kind of life” that multiplied in the sick organism, transmitted itself to another and contaminated it. Pasteur, however, in working with rabies, found that although the disease was contagious and transmitted by the bite of a rabid animal, the microorganism could not be observed. Pasteur concluded that the infectious agent was present but was too small to be observed under a microscope. In 1884, microbiologist Charles Chamberland developed a filter (known as a Chamberland or Chamberland-Pasteur filter) with pores smaller than a bacterium. By passing a solution containing bacteria through this filter, the bacteria were trapped in it and the filtered solution obtained became sterile. In 1886, Adolf Mayer demonstrated that tobacco disease could be transmitted to healthy plants by inoculation with extracts from diseased plants. In 1892, biologist Dmitry Ivanovsky used the Chamberland filter to demonstrate that crushed infected tobacco leaves remained infected even after filtering. Ivanovsky suggested that the infection could be caused by a toxin produced by the bacteria, but he did not persist in this hypothesis. In 1898, microbiologist Martinus Beijerinck independently repeated the experiment and became convinced that the filtered solution contained a new infectious agent, called contagium vivum

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