Hernan Espinoza espinoza at
Sat Jan 11 16:04:53 EST 1997

sesame at MCN.ORG (Ralph Gainey) writes:

>Dear Hernan:

>I would like to hear more details about mycoplasmas...

	Well, bearing in mind that I am not an expert in mycoplasma
biology, I'll do my best...

>is there an established field of study?

	Definitely.  Mycoplasmas are responsible for a wide range of
human infections especially in, but not limited to immune compromised
individuals.  The most common types are pnuemonias, I believe.  Nearer
and dearer to the hearts of many molecular biologists is the fact that
mycoplasma contamination of cell culture lines is a royal pain in
the posterior.

	In addition, because they are really just stripped down
bacteria, mycoplasmas have the smallest genomes for cellular
organisms.  The first (non-viral) genome that was completely
sequenced a couple of years ago was a mycoplasma.

> In which hosts are these intracellular parasites found?

	Most eukaryotes (including you), although the best studied
varieties are the one that cause human diseases (TB and chlamydia, to
name a couple).

>How many kinds have been identified?

	Hundreds, at least, I'll wager..but I don't know for sure.

> Do they have their own DNA?


> Mitochondria? Chloroplasts? Other?

	No and No.  Mycoplasmas are prokaryotes (like bacteria), they
don't even have nuclei.  They are about as simple as you get in terms
of cells, just a bag of chemicals (well, not quite that simple, but
much simpler than any eukaryotic cell).  They have all of the machinery
to replicate their own DNA, transcribe it to RNA, and translate it
into proteins.  What they lack is the full range of biosythetic 
pathways needed to make all of the chemicals need fo survival.  That's
why they have to parasitize eukaryotic cells, our cells can make some
of the chemicals they can't make for themselves.

>                                                             Living systems
>are very opportunistic, exploring every potentiality, and it seems possible
>that some type of cooperativity [symbiosis?] was involved in the development
>of higher levels of organization.

	That's the current theory for the origins of mitochondria and
chloroplasts...pretty neat if you ask me.  However, where mitochondria
and chloroplasts help us live, mycoplasmas are mainly there for the
free ride. 

	Well, I hope this kind of helped.  If you really want to
know more, you should go by your local university library and look
for a good prokaryotic biology textbook.  Heck, there might even
be a good one for mycoplasmas alone.  -Hernan

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