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Viruses are considered by some biologists to be a life form, because they carry genetic material, reproduce, and evolve through natural selection, although they lack some key characteristics, such as cell structure, that are generally considered necessary criteria for defining life.
Life-cycle of a typical virus (left to right); following infection of a cell by a single virus, hundreds of offspring are released. When a virus infects a cell, the virus forces it to make thousands more viruses. It does this by making the cell copy the virus's DNA or RNA, making viral proteins, which all assemble to form new virus particles. [37]
They lack nuclei but contain other organelles that assist with the replication processes. Viruses are sometimes considered akaryocytes but the suffix "cyte" means cells. Akaryote is also used as a synonym for akaryocyte however 'ote" implies a taxonomic relationship that does not exist among akaryocytes. [1]
Non-cellular life, also known as acellular life, is life that exists without a cellular structure for at least part of its life cycle. [1] Historically, most definitions of life postulated that an organism must be composed of one or more cells, [2] but, for some, this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements.
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 ...
When the virus replicates faster than the immune system can control, it can destroy cells and harm the body, and it can even incite an over-zealous immune reaction that can cause other damage.
A virus such as tobacco mosaic virus is not a cell; it contains only its genetic material, and a protein coat. Viruses are not typically considered to be organisms, because they are incapable of autonomous reproduction , growth , metabolism , or homeostasis .
Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms. Viruses are classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause.