Nucleus as a symbiote?

[Guest jbbrat01]

Hello everyone. I'm a student at the University of Louisville in the bio dept. I am concentrating my studies in subcellular biology and genetics.

 

I was reviewing some notes about the nucleus and other organelles present in eukaryotes and started to recall symbiotic theory about some organelles were bacterial or archea ancestors that fused with the host cell. Anyway, my question is:

 

Is the nucleus of eukaryotic organisms regared as a bacterial/archeal cell that fused with a host cell? If so, what are the probable species that would most resemble a modern nucleus?

[LucidDreamer]

I have actually heard that theory before. The host cell formed a symbiotic relationship with an early prokaryotic cell that had useful code. Then at some point the host's DNA, which was contained in the cystol, merged with the symbiot's DNA, forming the nucleus. I think the more popular theory is that the nucleus evolved from mutations that caused increasing plasma membrane infoldings. Of course, any species alive then is not likely to be around today, but if you are asking whether a nucleus appears to be more like an eubacteria or archeabacteria I don't know if we know that answer. The nucleus is mostly just an envelope containing DNA now so if the nucleus really did form from a symbiotic relationship then identifiable features may have been lost over the years.

[Guest jbbrat01]

Thanks. And, more clearly and rephrased, my question was: Is the nucleus the result of a symbiotic relationship or continued invagination of the plasma membrane (like ER, golgi, etc.) to protect nuclear DNA?

 

Further, what type of bacteria (not eubac or archeabac) could have it evolved out of?

It really would be a unique bac that I've frankly never heard of. Of course not all organelles are probably the result of symbiosis.

 

Any thoughts?

 

Btw, I am SO into lucid dreaming!

[LucidDreamer]

I haven’t read any overwhelming evidence for either. My gut feeling says invagination. I don't have alot of reasoning besides the other organelles of symbiotic origin have separate DNA and specialized purposes, while the nucleus contains the cells main DNA without any other purpose besides the protection of the Cell. Also, like you said there are already examples of invagination in Eukaryote.

 

I believe that chloroplast, plastids, and mitochondria are considered to have symbiotic origins. The chloroplasts were obviously some sort of photosynthetic bacteria. The mitochondria were a prokaryote that learned to use oxygen as a reducer, taking advantage of the photosynthetic bacteria’s oxygen byproduct. The host was probably some kind of ameba like creature that ate other kinds of prokaryotes for food then later evolution stepped in. The mutation that allowed the symbiosis was very beneficial. The mitochondria were incorporated first.

 

So I was strongly leaning towards invagination but now I am not so sure. Here are a couple of interesting articles. Both claim that the Eukaryotic cell is a hybrid of Eubacteria and Archeabacteria. Eukaryotic cells have similiarties to both.

 

I found a couple of really interesting sites about it.

http://www.astrobio.net/news/article243.html

http://biosci.usc.edu/documents/bisc121-fuhrman_103103.pdf

 

P.S. Ill start a thread about lucid dreaming tomorow.