acellular adj : not made up of or divided into cells [syn: noncellular] [ant: cellular]

Non-cellular life is life that exists without cells. This term usually is applied to earth-based life, and presumes the phylogenetic classification of viruses as lifeforms.

In discussing the taxonomic domains of life, the terms Acytota or Aphanobionta are occasionally used as the name of a viral kingdom, domain, or empire. The corresponding cellular life name would be Cytota. Non-cellular organisms and cellular life would be the only two subdivisions of earthly life -- also known as terrestrial organisms, Biota, Naturae, or Vitae.

The issue of life without cellular structure came to the fore with the 2003 discovery that the large and complex Mimivirus can make some proteins that are involved in the synthesis of proteins. This discovery suggests the possibility that some viruses may have evolved from earlier forms that could produce proteins independent of a host cell. If so, there may at one time have been a viral domain of life. Also, since most viruses have not been isolated and studied, it is theoretically possible that there may still be some undiscovered viruses on Earth that can produce their own proteins without the aid of a host cell. It is not clear that all small viruses have originated from more complex viruses by means of genome size reduction. A viral domain of life may only be relevant to certain large viruses such as nucleocytoplasmic large DNA viruses like the Mimivirus.

When considering non-cellular life, besides viruses, other forms might also be included, like viroids, satellites, transposons, plasmids, phagemids, cosmids, fosmids and prions.

The notion of non-cellular life has also occurred in debates about the possible forms of extraterrestrial life.

See also

• Alternative biochemistry