What is a Virus?

 

DEFINITIONS

VIRIONS
OTHER VIRUS-LIKE AGENTS

 


Viruses

Viruses may be defined as acellular organisms whose genomes consist of nucleic acid, and which obligately replicate inside host cells using host metabolic machinery and ribosomes to form a pool of components which assemble into particles called VIRIONS, which serve to protect the genome and to transfer it to other cells.

They are distinct from other so-called VIRUS-LIKE AGENTS such as VIROIDS and PLASMIDS and PRIONS

 


Alternative definitions:

S Luria et al.     AJ Cann

And EP Rybicki, 2008:

A virus is an infectious acellular entity composed of compatible genomic components derived from a pool of genetic elements.


The concept of a virus as an organism challenges the way we define life:

By older, more zoologically and botanically biased criteria, then, viruses are not living. However, this sort of argument results from a "top down" sort of definition, which has been modified over years to take account of smaller and smaller things (with fewer and fewer legs, or leaves), until it has met the ultimate "molechisms" or "organules" - that is to say, viruses - and has proved inadequate.

If one defines life from the bottom up - that is, from the simplest forms capable of displaying the most essential attributes of a living thing - one very quickly realises that the only real criterion for life is:


The ability to replicate


and that only systems that contain nucleic acids - in the natural world, at least - are capable of this phenomenon. This sort of reasoning has led to a new definition of organisms:


"An organism is the unit element of a continuous lineage with an individual evolutionary history."


The key words here are UNIT ELEMENT, and INDIVIDUAL: the thing that you see, now, as an organism is merely the current slice in a continuous lineage; the individual evolutionary history denotes the independence of the organism over time. Thus, mitochondria and chloroplasts and nuclei and chromosomes are not organisms, in that together they constitute a continuous lineage, but separately have no possibility of survival, despite their independence before they entered initially symbiotic, and then dependent associations.

The concept of replication is contained within the concepts of individual viruses constituting continuous lineages, and having an evolutionary history.

Thus, given this sort of lateral thinking, viruses become quite respectable as organisms:


More views on viruses and their definition:

 

http://microbiologybytes.wordpress.com/2007/07/24/its-life-jim-but-not-as-we-know-it/

It’s Life, Jim, but not as we know it… MicrobiologyBytes via kwout

 

http://microbiologybytes.wordpress.com/2007/06/26/a-feeling-for-the-molechism/

A feeling for the molechism* MicrobiologyBytes via kwout


DEFINITIONS

VIRIONS
OTHER VIRUS-LIKE AGENTS

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Copyright Ed Rybicki, October 1995; April, June,1998; May 2008