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From: lucius@mit-prep.ARPA (Lucius Chiaraviglio)
Newsgroups: sci.bio
Subject: Re: Life Classification
Message-ID: <104@mit-prep.ARPA>
Date: Mon, 18-May-87 20:53:01 EDT
Article-I.D.: mit-prep.104
Posted: Mon May 18 20:53:01 1987
Date-Received: Sat, 23-May-87 18:31:11 EDT
References: <9543@duke.cs.duke.edu> <1125@ius2.cs.cmu.edu>
Reply-To: lucius@prep.UUCP (Lucius Chiaraviglio)
Distribution: world
Organization: The MIT AI Lab, Cambridge, MA
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>In article <396@its63b.ed.ac.uk> simon@its63b.ed.ac.uk (ECSC68 S Brown CS)
>writes:
>>I can't remember what the fundamental differance between the eukaryotes
>>and the prokaryotes is, or even if there really is one at all! I do remember
>>that all the prokaryotes are haploid, so it would be very nice and convenient
>>if the eukaryotes were all diploid, wouldn't it? Anyone know anything about
>>any of this?

	Paul Gallagher said most of what needed to be said about the
differences between prokaryotes and eukaryotes, but I should also add that
eukaryotes can have any sorts of ploidys.  Organisms are known which are
monoploid (haploid) all the way up to at least octaploid, with gradations into
situations where the various genomes are different enough that they can no
longer be called copies of each other, although the organism is still called
polyploid because the genomes are similar, all the way to the point where all
the genomes are very different and cannot do with each other, at which point
they have merged.  Also, some organisms are known that do not have integer
numbers of copies of their genomes -- these include things as diverse as
ciliated protozoa which have macronuclei in which the genes are present in
huge numbers of copies but the spacers between genes have been mostly degraded,
and some insects such as scale insects in which all cells except the germ cells
lose certain chromosomes.

In article <1991@husc6.UUCP> gallagher@husc4.UUCP (paul gallagher) writes:
> . . .eukaryotes have more than 1 chromosome, with histones.

	Except for some such as dinoflagellates, which seem to have no
histones, although they do have some proteins associated with their DNA.

>                                                              Prokaryotes do
>not have a nucleolus, endoplasmic reticulum, golgi apparatus, mitochondria,
>lysosomes, or microtubules, while all eukaryotes do. Prokaryotes have ribosomes
>that are 70 S long, while eukaryotes have 80 S ribosomes (except in their
>mitochondria and chloroplasts).

	But see note about urkaryotes below. . .

	Also, 'S' is not a unit of length.  It is a measure of sedimentation
velocity, which is dependant on weight, density, and shape.  I don't
rremember its exact composition (it has a 10**13 and a seconds somewhere in
there, but I don't remember whether they are in the numerator or the
denominator), but units of length and molecular weight are definitely
absent from it.  (I should really remember exactly what it is -- I'll go look
it up, but not now.)

>I think it is believed that the Progenotes - the ancestral cells - gave rise
>to the Archebacteria, Eubacteria, and the Urkaryotes (a completely extinct
>kingdom).  Apparently, eubacteria started living inside urkaryotes and this
>was the first eukaryote (or protist). . . .

	According to a commentary in a recent issue (2 - 3 weeks ago) of
either Science or Nature (I think the latter), some urkaryotes (though the
article did not name them that, calling them primitive eukaryotes instead) may
still be around, and Giardia may be among these.  They had examined a
different parasitic organism, and found that although it had a nucleus and
either Golgi apparatus or endoplasmic reticulum (I forget which) as is
characteristic of eukaryotes, it lacked mitochondria and microsomes, and had
70S ribosomes which were approximately equally unrelated to both prokaryotic
and eukaryotic ribosomes (according to inspection of their nucleotide
sequences, that is).  While they did not examine the ribosomes of Giardia and
its free-living relatives, they have the other characteristics of these
above-mentioned parasites, and some of the free-living ones manage to use
oxygen without either mitochondria or peroxisomes (details not given).  Also,
some of these candidate urkaryotes have sizes characteristic of prokaryotes.

-- 
	-- Lucius Chiaraviglio
	   seismo!tardis!lucius
	   lucius@tardis.harvard.edu