What is Non-Cellular Life?
Mary McMahon
Non-cellular life is life which exists without a cell structure. Until the 21st century, people generally accepted that in order to be considered a life form, an organism had to have a cell, although cell structure could vary considerably. This excluded things like viruses from a list of "living" organisms. Additional research, however, suggested that this classification might be erroneous, and that things such as viruses could actually be considered life forms. This gave rise to the term "non-cellular life" to describe such organisms, differentiating them from cellular life like bacteria, fungi, archaea, protists, animals, and plants.
While people had suggested that viruses had many traits associated with life, it wasn't until 2003 that researchers discovered a virus with protein-making capabilities. The ability to synthesize proteins is considered a major factor in determining whether or not an organism is alive, and most viruses must hijack cells in order to build proteins. The fact that the Mimivirus can create proteins led to the realization that there might be more to viruses than meets the eye.
Given the large number of as-yet undiscovered viruses in the world, it is entirely possible that researchers may one day find more viruses capable of producing proteins. This would suggest that viruses perhaps evolved from earlier life forms which were capable of producing proteins independently of a cell. It also broadens the horizons considerably when thinking about extraterrestrial life; if non-cellular life exists on Earth, it may be found elsewhere as well.
In addition to viruses, structures such as cosmids, satellites, viriods, fosmids, prions, phagemids, and transposons may also be considered non-cellular life. Some scientists refer to non-cellular life as Acytota or Aphanobiota, and cellular life as Cytota. If the concept of non-cellular life grows to be more widely accepted, Acyota or Aphanobiota may be added to the three-domain system in taxonomy, turning it into a four-domain system which can be used to classify all forms of life on Earth.
Recognition of viruses as a legitimate life form may also deepen human understanding of these fascinating and complex organisms. Like cellular life forms, viruses clearly have their own agenda and life goals, although these goals may conflict with human, animal, and plant interests at times. The fact that some viruses are capable of producing proteins could also become a factor in treatment of certain viral infections, as medications could potentially be devised to target these proteins and eradicate the virus.
Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.
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Discussion Comments
@SkyWhisperer - I’d like to point out that scientists have created synthetic material in the laboratory and inserted them into living cells. It’s almost like creating a virus.
This is not the same thing as creating life, since the host cell already existed, but it’s getting us pretty close to that goal.
What’s important to note, I think, is that the synthetic material, while not cellular in itself, would not be considered non cellular “life.” I don’t think it falls in that category because it’s the cell that is living; the ability to create life is still a far way off, I believe, but I believe that viruses have provided scientists with a model to mimic.
@everetra - Cellular or non cellular, there is one restriction for any form of life as we know it today: it requires water.
Therefore when asking what forms of life could exist in other parts of the universe, we are unable to get away from this basic requirement.
Nothing on Earth suggests the possibility that we could find life that could exist without water. If we did, that would be the real breakthrough in the search for extraterrestrial life in my opinion, because it would open up for us planets in which there is little or no water.
@nony - I don’t think that’s what the article is suggesting.
Remember how viruses work. They need a host cell in order to survive (the article says they “hijack” a cell). Therefore a host cell must exist – no host cell, no virus. It’s kind of a chicken and egg thing if you want to look at it that way.
I believe the science is settled that the first forms of life were cellular; they may have been really simple cells that later evolved to more complex structures.
Viruses spun off from other forms of life and attached themselves to cells. That’s my understanding anyway.
Would it be possible then that the first forms of life were non cellular? I wonder if that is the implication of this article since viruses themselves are not cellular.
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