Re: Ribosomes

Dr Alan Mills (
Mon, 25 Mar 1996 19:29:29 +0000 (GMT)

Hi all,

On Mon, 25 Mar 1996, John Walshaw wrote:
> Here are some points about ribosomes which cropped up in the BioMOO
> today- can any cell biologists help?
> In textbooks it says something to the effect that mitochondria and
> chloroplasts 'contain complete genetic systems', but that the proteins
> which mediate these systems are mostly encoded by the nuclear genome.

Many nuclear encoded *proteins* are imported into the mitochondrion to
support its functioning. The mitochondrial genome is "streamlined" and
missing necessary components.

> By the way, I seemed to remember from my undergraduate cell biology (some
> time ago admittedly) that some of the rRNA molecules of cytoplasmic
------------------------8<-------------- snip
> But is it correct to assume that the products of these mitochondrial genes

Don't know about *rRNA* traffic between the compartments ;(

> Another thing- the implications of the different genetic codes found in
> 1)chloroplasts 2)mitochondria and 3)both prokaryotes, and eukaryote
> nuclear genomes.
> What are the implications for the endosymbiont theory for the origin of
> these organelles (i.e. one prokaryote ingesting another prokaryote). I
> can think of a couple of points, but can anyone enlighten us?

It has recently been discovered that *some* bacteria have variations from
the normal genetic code (in at least one codon). Prof.Mike Tutte at
Univ.Canterbury at Kent has been involved in establishing this, but I
don't have the references to hand. I seem to also remember that there
are variations in the code used in some viruses. I think a lot more work
will be needed to before we know how variable the genetic code is, let
alone speculation about the evolutionary origins/pathways.


Alan Mills at Venus Internet Ltd, 24 Denmark Street, London WC2H 8NJ, UK web:
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