Why are viruses not classified as cells




















Viruses do not metabolize. They do not have cells. They cannot reproduce independently. A coronavirus, for example, is a nanoscale sphere made up of genes wrapped in a fatty coat and bedecked in spike proteins.

Still, viruses have many traits of living things. They are made of the same building blocks. They replicate and evolve. Once inside a cell, viruses engineer their environment to suit their needs — constructing organelles and dictating which genes and proteins the cell makes. Recently discovered giant viruses — which rival the size of some bacteria — have been found to contain genes for proteins used in metabolism, raising the possibility that some viruses might metabolize.

Plus, almost every rule that excludes viruses from the land of the living has its own exceptions. For example, Rickettsia bacteria are classified as living but, like viruses, can multiply only within other cells. All living things, in fact, rely on other living things. A single rabbit cannot replicate on its own, but a rabbit is definitely alive, right? For these reasons and others, the debate over whether viruses are alive or not continues today.

In , virologists Marc H. Or maybe a virus can be both nonliving and alive. In , biologist Patrick Forterre of the Pasteur Institute in Paris argued that viruses alternate between an inactive state outside a cell and a living, metabolically active state inside a cell that he calls the virocell.

For Forterre, viruses are like seeds or spores. They have the potential for action and that potential can be extinguished. While debates over classification can at times feel frivolous, in reality how we talk about viruses affects how they are researched, treated and eradicated. Personifying viruses as villains and menaces interferes with a real understanding of evolution and nature, says Colin Hill , an infectious disease specialist at University College Cork in Ireland.

Life is the manifestation of a coherent collection of genes that are competent to replicate within the niche in which they evolve d. Viruses fulfil this definition. It is estimated that there are 10 31 virus particles in the oceans — they vastly outnumber all other organisms on the planet. Alive or not, viruses are doing rather well! University of Edinburgh [email protected].

Bamford, D. Evolution of viral structure. Theor Popul Biol 61, — Boyer, M. Phylogenetic and phyletic studies of informational genes in genomes highlight existence of a 4 th domain of life including giant viruses. Moreira, D. Ten reasons to exclude viruses from the tree of life. Nat Rev Microbiol 7, — and associated commentary. Nasir, A. A phylogenomic data-driven exploration of viral origins and evolution.

Sci Adv , e Rybicki, E. A top ten list for economically-important plant viruses. Arch Virol. Scheid, P. Viruses in close associations with free-living amoebae.

Parasitol Res , — Image: Coloured transmission electron micrograph of a group of foot-and-mouth disease viruses. Human adenovirus type 5 and sulfolobus turreted icosahedral virus 2. David Bhella. Are viruses alive? Issue: What is life? Back to issue. We've got the study and writing resources you need for your assignments.

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