Overview of Virus (part 1)
1. Introduction
(Latin for ‘poison’) organizational entities composed only of genetic material surrounded by a protective envelope. The term virus was used in the last decade of last century to describe the disease-causing agents smaller than bacteria. Lack of independent living but can replicate inside living cells, often damaging to his guest in this process. The hundreds of known viruses are the cause of many different diseases in humans, animals, bacteria and plants.
The existence of viruses was established in 1892, when Russian scientist Dmitry I. Ivanovsky, found microscopic particles, known later as the snuff mosaic virus. In 1898 the Dutchman botanist Martinus W. Beijerinck called these particles infectious virus. A few years later, viruses were found growing on bacteria, which are called bacteriophages. In 1935, the American biochemist Wendell Meredith Stanley crystallized the snuff mosaic virus, showing that consisted only of genetic material called ribonucleic acid (RNA) and an envelope protein. In the 1940s the development of electron microscopy enabled the visualization of the virus for the first time. Years later, the development of high-speed centrifuges able to concentrate and purify. The study of animal virus reached its peak in the 1950s with the development of cell culture methods, support of viral replication in the laboratory. Then they discovered many viruses, most of which were sampled in the 1960s and 1970s, in order to determine their physical and chemical characteristics.
2. Features
Viruses are submicroscopic intracellular parasites, consisting of RNA or deoxyribonucleic acid (DNA)-never both-and a protective layer of protein or lipid components combined with protein or carbohydrate. In general, the nucleic acid molecule is a unique single or double helix, however, certain viruses have genetic material segmented into two or more parties. The outer covering is called a capsid protein and the subunits that compose it, capsomeres. It’s called nucleocapsid, the set of all elements. Some viruses have an additional envelope usually acquired when the nucleocapsid exits the host cell. The complete viral particle is called a virion. Viruses are obligate intracellular parasites, ie only replicate in cells with active metabolism, and outside them are reduced to inert macromolecules.
The size and shape of the viruses are highly variable. There are two basic structural groups: isometric, rod-shaped or elongated, and complex virus with head and tail (as some bacteriophages). The smallest viruses are icosahedral (20-sided polygons) that measure between 18 and 20 nanometers wide (1 nanometer = 1 millionth of 1 mm). The larger ones are elongated, some measuring several micrometers in length, but rarely measure more than 100 nanometers wide. Hence the virus longer have a width that is below the limits of resolution of light microscopy used to study bacteria and other microorganisms.
Many viruses with helical internal structure have outer shell (also called decks) composed of lipoproteins, glycoproteins, or both. These viruses are like spheres, but may have different shapes and size ranges from 60 to more than 300 nanometers in diameter. Complex viruses, such as some bacteriophages, have heads and a tubular tail that binds to the host bacterium. The brick-shaped poxvirus and a complex protein composition. However, these latter types of virus are exceptions and most have a simple way.
credit to: MartÃn Buczyner