Re: Can organelles like the mitochondria live out side of the cell?

Dear Jesse:

Organelles have evolved a symbiotic relationship w/ their host cells.  Even though they still carry their own genomic DNA, it no longer encodes all of the gene products necessary for their independent function.  So as you suspected, they are completely dependent upon their host cell for survival & would cease to function if 'disconnected', just like an organ if disconnected from the body.

However as you may know, it is possible for some cells comprising organs to survive & grow independent of their host organism under the proper culture conditions.  So the most intriguing part of your question is whether or not isolated organelles can survive, function, & replicate if provided w/ the proper culture conditions duplicating the cytoplasmic environment inside their host cells, just as cells can grow outside of their host organism under appropriate culture conditions.

Although it would seem to be a distinct possibility, the current state of our knowledge appears to be capable of providing culture conditions (i.e. essential nutrients, salts, etc.) under which organelles can temporarily survive & function, but not replicate.  This is probably because their replication is very tightly coordinated w/ that of their host cell.  It is currently not possible to duplicate the complex cytoplasmic signals controlling cell division in culture.  So in answer to your question as to whether or not organelles can 'live' on their own, they have not yet been observed to reproduce themselves outside of their host cell, a requisite property for living organisms.

However, effective replication of isolated cells in culture has only been perfected over the past ~60 yrs.  So it is certainly possible that culture conditions supporting organelle replication may also be perfected in the near future, possibly in your lifetime.  This may be driven by increasing research interest in the numerous mitochondial diseases, which may be better studied in an isolated mitochondrial culture system.

Thanks very much for your excellent questions,

Jeff Buzby, Ph.D.
CHOC Research Institute