Simplest known organism?

[Tweek888]

I was just wondering what the simplest known organism is?

 

Sorry if this is a stupid question...

[ecoli]

not stupid at all... although there is no easy answer, especially because the word "simple" is pretty arbitrary.

 

I believe that the simpliest organisms were protobionts, which is basically when organic molecules started aggregating to form the first primitive lifeforms. These are even less complex then archeobacteria... though I'm entirely sure that they still exist.

http://www.biocab.org/Protobiont.html

[bascule]

There's also the "progenotes" which lie between the soup of the theorized "RNA world" and the common ancestor of all life on earth today. They're the ones who started harnessing the power of DNA and protein and encapsulating themselves into the first cells and were thus self-contained replicators

[Tweek888]

Cool!

 

In addition is there any information on how the organism transitioned to a living organism?

[Helix]

Through natural selection the very simple life started to slowing accumulate advantages and changes that led it to become more advanced. Eventually unicellular organisms gave way (but still existed) to multicellular ones. Simply put, they evolved through natural selection.

 

But what about viruses? They are very simple but require multicellular life to live. How could viruses hang around, untouched by evolution, waiting for plants and dinosaurs to eventually show up?

[bascule]

Cool!

 

In addition is there any information on how the organism transitioned to a living organism?

 

I would assume that the organisms with better external defense and replication properties simply devoured the less progressively evolved descendants of their ancestors and, per the laws of natural selection, the most reslient won out.

 

We're talking about a time of extreme "cannibalism" when the reactions which couldn't sustain themselves became food for their siblings.

 

If what you're really asking about is abiogenesis, Dawkins (and therefore I, being an unabashed Dawkins worsipher) says the secret lies in autocatalysts. Catalysts are specially shaped molecules which suck up two other molecules and mash them together to create a product, and thus they speed up chemical reactions. Autocatalysts have the unique property that the product they create is themselves, so once an autocatalyst forms, if it's in the presence of the molecules it catalyzes then it creates a whole bunch of copies of itself.

 

In experiments performed by Julius Rebek and his colleagues at the Scripps Institute in California, they combined amino adenosine and pentafluorophenyl ester with the autocatalyst amino adenosine triacid ester (AATE, which, being an autocatalyst, catalyzes the combination of the afforementioned chemicals into more amino adenosine triacid ester)

 

Rebek and his team found a system in which more than one variant of the autocatalysed substance existed. Each variant catalysed the synthesis of itself, using its preferred variant of one of the ingredients. This raised the possibility of true competition in a population of entities showing true heredity, and an instructively rudimentary form of Darwinian selection.

 

It's likely something like this happened either with collections of RNA molecules or that other autocatalyzing compounds "recruited" RNA molecules to assist in their autocatalyzing reactions, and slowly RNA started taking on the role of both a catalyst and a storage mechanism for self-replication "instructions", i.e. heredity.

[bascule]

But what about viruses? They are very simple but require multicellular life to live. How could viruses hang around, untouched by evolution, waiting for plants and dinosaurs to eventually show up?

 

Viruses involved in tandem with the cells their infection vectors proved successful for. As long as one virus is constructed in such a way that it can successfully infect one cell and thus make a multitude of copies of itself, the particular strain will continue to evolve.

[Helix]

Viruses involved in tandem with the cells their infection vectors proved successful for. As long as one virus is constructed in such a way that it can successfully infect one cell and thus make a multitude of copies of itself, the particular strain will continue to evolve.

 

 

But that's not advantageous from an evolutionary standpoint. The host, being unicellular, would die immediately and therefore the virus would only make a few copies, not enough to flourish...what a way to live for millions of years (until multicellular life arose).

[Tweek888]

Maybe the virii came later? after multi-celled organisms?