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A virus with this "viral envelope" uses it—along with specific receptors—to enter a new host cell. Viruses vary in shape from the simple helical and icosahedral to more complex structures. Viruses range in size from 20 to 300 nanometres; it would take 33,000 to 500,000 of them, side by side, to stretch to 1 centimetre (0.4 in).
Capsids are broadly classified according to their structure. The majority of the viruses have capsids with either helical or icosahedral [2] [3] structure. Some viruses, such as bacteriophages, have developed more complicated structures due to constraints of elasticity and electrostatics. [4]
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.
Such viruses made it difficult to properly obtain X-ray diffraction results. [3] In response to this, cryogenic electron microscopy (cryo-EM) emerged as a new, alternative method for studying virus structures. Cryo-EM enables scientists to visualise viruses at near-atomic resolution without crystallisation. [3]
The structure of the capsid allows the virus to use a small number of viral genes to make a large capsid. [3] Several protomers, oligomeric (viral) protein subunits, combine to form capsomeres, and capsomeres come together to form the capsid. [1]
While the terms "virus" and "virion" are occasionally confused, recently "virion" is used solely to describe the virus structure outside of cells, [3] while the terms "virus/viral" are broader and also include biological properties such as the infectivity of a virion.
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 ...
During assembly of the bacteriophage (phage) T4 virion, the structural proteins encoded by the phage genes interact with each other in a characteristic sequence. Maintaining an appropriate balance in the amounts of each of these structural proteins produced during viral infection appears to be critical for normal phage T4 morphogenesis. [4]