The Theory of Eukaryotic Cell Origin

Within the cells of Eukaryotes lie many organelles.  The Mitochondria and Chloroplasts are examples of said organelles that provide the Eukaryotic cell with a certain function or process that benefits the cell.  Interesting enough, these two organelles actually have their own DNA, separate from the DNA of the cell itself.  So what does that propose?

Did the Mitochondria and Chloroplasts originate within the cell from the beginning?  Or were they actually bacterium that were absorbed slowly over time into the cell and assimilated?

This is the Endosymbiotic theory.  The theory states that the Mitochondria and the Chloroplasts originated as bacterium long before Eukaryote cells became what they are today.  Based on the information that the Mitochondria and the Chloroplasts have their own separate and unique DNA and share similar characteristics with bacteria, it is very possible that this theory is indeed true!  Here is a link that discusses the theory and what it all means:

http://www.fossilmuseum.net/Evolution/Endosymbiosis.htm

So taking from that information, one can see how this theory poses a possible solution to the origin of the Eukaryotic cell that we see today!  The organelles could have originated from a family of bacteria and were at one point assimilated during a primary endosymbiosis action. 

Now this isn't a relatively new theory, it's been around for some time.  So none of this may seem like new news to some people.  But I decided to investigate further, and ask another question along with what was stated above.

If the Mitochondria and the Chloroplasts were a bacterium that was swallowed up by the cell, could other pieces within the cell have similar origins?  Say, the nucleus?

Now the nucleus is evident in almost if not all living cells found in the world today.  But what's strange is how different the nucleus is in a Eukaryotic cell when compared to the rest of the microbial world around us.  Bacteria and Archaea have a nucleoid, which is not membrane bound, quite the opposite of Eukaryotic cells.  So where did our membrane bound nucleus come from?

There is another theory that has been circulating around within the past 15 or so years of Viral Eukaryogenesis.  Basically, it proposes that the nucleus in our cells could have been a virus.

Yup, a virus.  One that had a complex DNA genome within that when it infected the ancient Eukaryotic cell, the host genes and the viral genes combined to create a virion that established itself within the host cell; that when the virus introduced mRNA translation, linear chromosomes, and other viral characteristics to the host cell, it created a microenvironment where the virus had a much more efficient and beneficial role.  This theory is touched upon in these two links, the first being a quick summary of the theory and the second being a more detailed analysis of Viral Eukaryogenesis and Endosymbiosis:

http://www.ncbi.nlm.nih.gov/pubmed/11523012

http://www.intechopen.com/books/meiosis/meiosis-its-origin-according-to-the-viral-eukaryogenesis-theory

The second link is a long read, but it presents some absolutely amazing evidence that supports the theories listed in this post.

Above all, these theories aren't conclusive and set in stone, they are still theories.  But did our cells originate from bacterial, archaeal, and viral ancestors?  Were we the product of our ancient simple cells assimilating other forms of microbial life and become a more efficient cell?  We may eventually prove these theories to be utterly true, or come up with different evidence that would support an entirely different theory.  But the evidence is a little overwhelming, and our cells may have originated from Mother Nature deciding to have a little fun playing Dr. Frankenstein.