Hey Fathom!
The mitochondria stores mDNA(mtDNA) passed on by the mother of an organism, I know thisn because they use it as a way to track female heritage in animals and humans. This information has almost no effect on development of a human, but it is there.
RNA if i remember correctly has something to do with the transition of genes to proteins for basically translating the genetic code so the cell can make use of it, again I'm not too sure but RNA found in the mitochondia is a non coding form.
Evidence exists that mitochondria was once a seperate organism, The symbiotic relationship of the Mitochoindria and other living cells could have eventually led to the current configuration. They no longer have any specific purpose other than generating ATP.
But in a fictional reality the Mitochondria have developed an aweareness and have began to implement their own mutated DNA into the nucleus, by cutting off energy output to the cells and dedicating it to rapid evolution of the organalle itself. and changing beings physical form.
http://www.actionbioscience.org/evolution/ingman.html
Less credible but I'm too lazy to skim through my science text books.
http://en.wikipedia.org/wiki/Mitochondrial_DNA