The concept of life from a biological point of view refers to the capacities of metabolism, reaction to external stimuli, growth and reproduction, generally also to the capacities of being born and dying. The physical beings with these capabilities would be considered aliveUnlike the Inert beings.

The idea of ​​biological life has been closely linked to organisms with a cellular structure. However, the idea of acellular life it has never been ruled out, especially if one thinks of life in other parts of the Universe, a thought in which we do not have to take for granted that life would be structurally the same as that existing on Earth.

acellular life

The existence of acellular life forms on Earth is not an out of the question either. The line between being alive and being inert is very diffuse in some cases, highlighting the case of virus. For many the virus is not a living being, for many it is.

The definition of life that requires the simultaneous existence of metabolism, reaction to stimuli, growth and reproduction, is for many scientists to assume that life is as the scientist himself experiences it, and they argue that this assumption may be wrong. For example, some bacterial spores can remain ungrown for extremely long periods, even over a thousand years.1.

Mimiviruses and the definition of life

In 2003, a new virus was identified, the Mimivirusand it was found that it could synthesize their own proteinsa fact that launched many scientists to consider this virus as a living being.

Mimivirus is as big as some bacteria, similar to Rickettsia conorii oa Tropheryma whippiei. Among the 911 genes of the Mimivirus DNA, there are some that have not been found in any other virus and that until their discovery were thought to be exclusive to cellular life.

For example, they contain the gene for cytochrome P450 and other proteins involved in metabolism of carbohydrates, lipids and proteins. The Mimiviruses not dependent on host cell to encode these Metabolic routesas if it happens in some obligate intracellular prokaryotes that depend on these pathways encoded in the host cell and that are clearly considered living beings.

Mimiviruses do not depend on the host cell genome to encode some metabolic pathways but continue to depending on their ribosomes for genetic translation. They also do not possess some characteristics included in many definitions of life: homeostasis, response to stimuli, and growth (they replicate by self-assembly but do not grow in the common sense of the word).

Mimivirus is classified within the family Mimiviridaewhich is believed to have appeared on Earth a billion years ago, before cellular life arose. It is believed that they played a prominent role in the development of life on the planet, since there are still viruses of this family capable of infecting bacteria, archaea and eukaryotes.

Viruses are usually encompassed in the term acytoteeither aphanobiontawhich include other acellular biological entities such as plasmids, prions, transposons and viroids, also frequently referred to as probionts.

In the same way that the definition of life and its relation to the cell is very diffuse, assuming that life is based on DNA can be an equally erroneous assumption. Within the concept of “acellular life”, many scientists also include possible forms of extraterrestrial lifewhich may or may not use DNA, and even a possible artificial life future where machines are capable of reproducing themselves by manufacturing their own structural elements and evolve by improving and adapting to the environment.