From: uc-chan@mcl.ucsb.edu (Christina Callihan)
Newsgroups: rec.food.sourdough
Subject: Re: more on the biology of sourdough
Date: 28 Aug 92 17:11:45 GMT
Article-I.D.: mcl.uc-chan.715021905

In <1992Aug27.143822.24606@hemlock.cray.com> dadams@cray.com (David Adams) writes:

>Charles> == Charles Delwiche
>| == Christina Callihan

>Charles> This article is also of interest because it studied the
>Charles> plasmid content of bacteria in sourdough starter (if you know what
>Charles> that means, you might want to look at the paper).  
>|
>|Plasmids are little loops of DNA (genetic material) that are separate from
>|the main bacterial chromosome.  They are interesting because bacteria can
>|trade genetic information in a process called conjugation.  So you can
>|trace plasmids through different strains to see which ones have the same
>|loops.  Bacteria can acquire different traits (i.e. resistance to certain
>|antibiotics) by receiving the right plasmids.  

>So if I understand this, (let's see if I do) plasmids kind of relate
>to bacteria the way that mitochondria do to animal cells, or chloroplasts
>do to plant cells?

>Is the idea you mention that conjugation leaves the DNA in the plasmid
>unafected, hence allowing researchers to to trace the source of different
>strains of bacteria?   

>What function do the plasmids serve?  How do they benefit the bacteria.
>(Ie.  It seems that chloroplasts and mitochondria have mirror roles.
>Chloroplasts are responsible for photosynthesis--the process that changes 
>light energy into sugar.  Mitochondria are responsible for changing sugar 
>(or other fuel?) and converting it into ATP.  Did I get that right?  
>Does the plasmid have some mirror role?)

A plasmid, once it's in a bacterium, is duplicated, expressed and generally
treated the same way the cell's own chromosome is.  For those of you who
weren't forced to study bacterial genetics ( :) ), bacteria have a loop of
DNA for their chromosome, instead of long strands that glom up into 
several chromosomes during cell division, like we have.  So plasmids can
be thought of as "mini-chromosomes", since they provide a template for
protein production, just like the "normal" chromosome.  They are much
smaller than the main chromosome though.

(By the way, if Charles or anyone else catches mistakes in what I'm 
passing along here, please correct me.  It has been a while since my
Modern Genetics courses.  :)  

In conjugation, a tube forms between a bacterium that has a particular
plasmid, and one that doesn't.  The plasmid is duplicated and fed through
the tube to the other cell.  I've forgotten whether or not this process
ever happens with the main chromosome. 

As for what "purpose", plasmids serve, it all depends on what kind of
proteins it codes for.  Scientists can even put together their own 
plasmids, introduce them into a bacterial culture, and then use them as
markers for tracing mutations and mapping the chromosome.  

I think I'm getting to the limits of what I can explain without resorting
to my textbook.  :)  Geneticists are doing so much with plasmid research
these days, there are probably tons of applications that I never studied.



____________________________________________________________________________
If You Know What |     Christina M. Callihan     |  Doing STRANGE THINGS
 You're Doing,   |  AKA C-chan, Bwee, Chrystal-  |  in the name of Art,
   It's Not      |   Elf & Who Knows What Else   |  and STRANGER THINGS
   Research!     |       (I sure don't)          |    in the name of
 => => => => =>  |     uc-chan@mcl.ucsb.edu      |       CHOCOLATE
----------------------------------------------------------------------------
	When life gets weird, the weird get a life.     :)
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(The opinions in this post are not endorsed by the University of California
at Santa Barbara....THANK GOODNESS!!!!!!!!!  ;^}  )
From: dwj@hpcndm.CND.HP.COM (Dave Jerzycki)
Date: Tue, 25 Aug 1992 15:18:55 GMT
Subject: Re: Bread machines
Organization: HP Network and System Management Division