Expert: Walter Hintz - 7/9/2005

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Has anyone noted plasmids in cyanobacteria and more importantly, in chloroplasts?
Answer -
Cyanobacteria are prokaryotes and contain their DNA in plasmids.. Chloroplasts are different organelles and do not contain plasmids

I QUESTION YOUR ANSWER.  SOME EUBACTERIA HAVE PLASMIDS ALONG WITH THEIR NUCLOID, THUS I WONDERED IF CYANOBACTERIA ALSO HAD THEM (HAS ANYONE SEEN THEM IN CYANOBACTERIA).  ALSO, IT IS CLEAR THAT CHLOROPLASTS ARE ENDOSYMBIOTIC CYANOBACTERIA, SO I WONDERED IF ANYONE HAD OBSERVED PLASMIDS IN THEM.  HOW ABOUT IN MITOCHONDIA?
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Hi Alan:  Of course both mitochondia and chloroplasts have DNA which lends credence to endosymbiosis but as far as I know mitochondrial DNA is not in the form of a plasmid.  I found an interesting paper about this.
  Go here:
http://www.bio.davidson.edu/Courses/Molbio/MolStudents/Spring2003/Austin/first.h

Thanks Walter:  a few tidbits still escape me.  Are we saying that mitochondira (and presumably chloroplasts also) have lost most all of their ancient DNA (to the nucleus) and now have only one small loop of DNA which seems to be analagous to a modern eubacterial nucleoid?  Modern bacteria (as I understand it) have a relatively large nucleoid and several similar, tiny plasmids.  Mitochondria then must have lost the nucleoid and have only a plasmid left - or - all the plasmids are gone, and the nucleid has been reduced to the size of a plasmid?  What think you?  Alan  

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I discovered a paper describing the mitochondrial DNA as being in 5 to 10 rings  These rings contain over 16,569 base pairs and 37 genes involved in respiration.  These rings are not called plasmids but I suppose they really are.  Therefore, as you suggest, most of the premodial DNA is no longer in the mitochondria.  Check this out at
 http://en.wikipedia.org/wiki/mitochondrial_DNA