[Phys-L] Re: Another attack on Evolution

[Bernard Cleyet <bernardcleyet@REDSHIFT.COM>]

I was going to argue that pro and eucaryotes were independent, but the
Canadian site below "set me straight".

bc


http://home.cc.umanitoba.ca/~oresniki/210/lecture%2013.html
<http://home.cc.umanitoba.ca/%7Eoresniki/210/lecture%2013.html>


Origin of Intracellular Organelles: Serial Endosymbiosis Theory (SET):
Box 4.1, p.83. Some features of organelles resemble procaryotic
organisms, e.g., size, type of  DNA, ribosomes and reproduction. The
similarities suggest that the organelles may have evolved from procaryotes.

- All organisms evolved from the a common ancestral organism called the
progenote that arose -4 billion years ago. The progenote gave rise to 3
cell types, i.e., eubacteria, archaebacteria and urcaryote or
protoeucaryote  (ancestral eucaryote lacking lacked organelles).

- The origin of the protoeucaryote is not known, but it was likely a
unicellular eukaryote with a membrane-bound nucleus, but no organelles
(mitochondria, chloroplasts).  Eucaryotic microorganisms like this exist
today, e.g., diplomonads, microsporidia, entamoeba.

- SET proposes that the proposes that the protoeucaryote may have
phagocytosed an aerobic bacterium and, instead of being digested, the
bacterium survived in the phagocytic vesicle as an endosymbiont. The
bacterium would carry out respiration providing energy to the host,
whereas the host provide protection and nutrients that allowed the
endosymbiont to grow. Such endosymbiotic relationships between bacteria
and eukaryotic protozoa are quite common even today (transparency).

With time, the endosymbiont loses many of its bacterial characteristics
but continues in its function to to provide energy to the host cell
through respiration. Eventually, the endosymbiont evolved into the
present day mitochondria which still retains some bacterial
characteristics. Protozoa and fungi likely originated in this way.

By comparing certain genes in the mitochondrial genes with those of
present-day prokaryotes, it seems likely that that the orginal
endosymbiont was a bacterium related to a group of present-day bacteria
called the rickettsia. These are characterized as intracellular
parasites and are adept at growing within host cells.

- Similarly phagocytosis of a photosynthetic bacterium by protozoa may
have resulted in an endosymbiotic relationship in which the bacterial
endosymbiont provided energy to host cells through photosynthesis in
exchange for nutrients and protection. The endosymbiont may then have
evolved into a chloroplast leading to the evolution of the algae -
eukaryotic microorganisms possessing both mitochondria and chloroplasts.
 Again certain genes in chloroplast DNA are very similar to genes found
in present day cyanobacteria indicating the original endosymbiont may
have been a cyanobacterium. These are photosynthetic bacteria that
perform photosynthesis in the same manner as algae and plants.

Even today there are examples of stable endosymbiotic associations
between protozoa and cyanobacteria (transparency of Cyanophora paradoxa)



Larry Woolf wrote:

> (easier to read, I hope)
> =20
> =46rom: Forum for Physics Educators on behalf of Justin Parke
> Sent: Sat 1/21/2006 1:38 PM
> Subject: Re: Another attack on Evolution
>
> The problem as I see it is that while honest people do not dispute th=
> at evolution (i.e. changes within a species) occurs it has not yet be=
> en established to anywhere near the same level of indisputability tha=
> t all species evolved from a single or a few common ancestors.  I thi=
> nk your logical progression is misleading in that it assumes that sin=
> ce change within a species has been observed that all other postulate=
> s of evolutionary theory are therefore true.
> ---------------------------------------------------------------------=
> ---------------
>
> The evidence that species evolved from a common ancestor seems overwh=
> elming:
>
> 1. The perfect nesting taxonomy of all living things
>
> <http://www.evolutionary.tripod.com/dawkins_blindwatchmaker_1996_full=
> .pdf>=20
> page 256-  in the actual book (page 260- if you look at the paginatio=
> n at the bottom of the screen)
>
> "For evolutionary biologists there is something very special about th=
> e classification of living organisms, something that is not true of a=
> ny other kind of taxonomy. It follows from the idea of evolution that=
>  there is one uniquely correct branching family tree of all living t=
> hings, and we can base our taxonomy upon it. In addition to its uniqu=
> eness, this taxonomy has the singular property that I shall call perf=
> ect nesting. What this means, and why it is so important, is a major =
> theme of this chapter."
>
> See also chapter 11.
>
> 2. The common mechanism of replication (via DNA) of all living things=
> .
>
> Larry Woolf
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