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Author Topic:   Is the eukaryotic cell a colony?
caffeine
Member (Idle past 1135 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 1 of 17 (491765)
12-20-2008 8:49 PM


I was recently reading Climbing Mount Improbable by Richard Dawkins*, and was slightly jarred by his bald-faced assertion, towards the end of the book, that eukaryotic cells evolved as colonies of prokaryotes. I'm a long way from being a microbiologist, so my views may be slightly confused, but this doesn't satisfy me at all as an explanation of the origin of eukaryotes, and so I thought I'd turn to where I knew there were plenty of people better educated than me to offer their opinions.
I accept the fact that organelles like mitochondria, chloroplasts, and possibly peroxisomes are descended from originally independent organisms, but none of these seem to me to be essential, defining features of a eukaryotic cell. It seems perfectly conceivable to me to imagine an ancient eukaryotic cell, vastly bigger than prokaryotes, with a nucleus and an internal transit system, but without any endosymbiotic organelles. On the other hand, I don't see how the idea that eukaryotes are colonies explains much about eukaryotes that isn't explained by the idea of endosymbiotic cells becoming part of a pre-existing eukaryote.
If this isn't just a whim of Dawkins that I'm getting unjustly upset about, is there anything more to support the idea of colonies of prokaryotes forming eukaryotes?
*I'd recommend everyone to borrow it from a library and read the chapters on the eye, flight and fig trees. As for the rest of it, you can find better things to do with your time.
Edited by caffeine, : linguistic style

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AdminNosy
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From: Vancouver, BC, Canada
Joined: 11-11-2003


Message 2 of 17 (491777)
12-21-2008 1:33 AM


Thread moved here from the Proposed New Topics forum.

  
Wounded King
Member (Idle past 143 days)
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 3 of 17 (491840)
12-22-2008 6:17 AM
Reply to: Message 1 by caffeine
12-20-2008 8:49 PM


I accept the fact that organelles like mitochondria, chloroplasts, and possibly peroxisomes are descended from originally independent organisms, but none of these seem to me to be essential, defining features of a eukaryotic cell.
Indeed, the classic defining feature of a eukaryotic cell is that it has a membrane bound nucleus. It has been suggested that the nucleus itself could have an endosymbiotic origin. The order in which different characteristics of modern eukaryotic cells originated is pretty controversial. Lynn Margulis, one of the major proponents of the Serial Endosymbiotic Theory, puts forward a hypothesis where the initial symbiotic event was fusion with a spirochaete giving rise to a proto-flagellum and that as a consequence of this initial fusion the nucleus arose from the dissociation of the incorporated organisms enveloped genetic material from the proto-flagellum (Margulis et al., 2000).
I'm not sure that what Dawkins means is anything more than the 'community' of incorporated prokaryotes involved in endosymbiosis when he discusses colonies, i.e. a modern eukaryotic cell is a 'colony' of, albeit simplified, bacteria in the same way that he describes an elephant as a colony of eukaryotic cells.
I think that what Dawkins is describing is exactly the same as endosymbiosic theory, so I'm not sure why it wouldn't explain exactly the same things.
I don't see anything to get upset over.
TTFN,
WK

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pangor
Junior Member (Idle past 5684 days)
Posts: 1
From: Davao City, Mindanao, Philippines
Joined: 12-21-2008


Message 4 of 17 (491908)
12-24-2008 4:26 AM
Reply to: Message 1 by caffeine
12-20-2008 8:49 PM


Hey,
I am new... so this is my first post here. Hello all.
Could you give us a better idea of what he was actually claiming. I don't have easy access to a well equiped library... and I found your statement a little vauge. It sounds interesting, I would just like to hear a little more on the topic.
Cheers,
D
Edited by pangor, : Grammar

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caffeine
Member (Idle past 1135 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 5 of 17 (492330)
12-30-2008 7:42 AM


Sorry it's been so long without a reply - haven't been around a computer much over Christmas.
I forget exactly what Dawkins wrote, and I don't have the book here to check, but he didn't discuss the matter in any detail at all. He basically just wrote that eukaryotes were formed by bacteria living together in colonies. I think my ire was raised a bit just by the way he'd declared as brute fact what I understood to still be controversial and debated.
What little I know of cell biology I learnt from reading Christian De Duve, who seems to be of the opinion that endosymbiosis cannot explain most of the features of eukaryotes. His preferred hypothesis was that eukaryotes predate endosymbiosis, with much of their features being explained simply as corollaries of increasing size, with the nucleus just evolving as the bacteria's DNA is caught in an infold in the cell's membrane (which sort of thing creates the whole internal membrance system). I'd have to go and read it all again to remember more details.
The idea of an already huge (by bacterial standards) cell engulfing mitochondria and the like and them surviving inside their host to gradually become a part of it made more sense to my untrained eye than the idea that huge cells arose through successive little cells joining together. I'll admit that my knowledge is limited on what's actually being proposed though - I'll try reading that Margulis article.
I suppose what I was basically trying to find out was how controversial are hypotheses like de Duve's. CLearly I have a lot more reading to do on this.

Replies to this message:
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Dr Jack
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Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003


Message 6 of 17 (504215)
03-25-2009 10:49 AM
Reply to: Message 5 by caffeine
12-30-2008 7:42 AM


Hi Caffeine,
Resurrecting an old thread I know, but I found something today linked to this so I thought I'd pop you the link.
As Wounded King outlines Dawkins is referring to Margulis's idea about the origin of various features of the Eukaryotic cell via endosymbiosis. It's now widely accepted that some organelles, noteably Mitochondria and Chloroplasts, were acquired by endosymbiosis.
Margulis's original idea included the notion that cilia also started as endosymbiotic bacteria. It is now known that this idea is incorrect, see this paper on the evolution of the eukaryotic cilium (aka flagellum)

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Replies to this message:
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 Message 16 by straightree, posted 04-05-2009 5:48 AM Dr Jack has replied

  
caffeine
Member (Idle past 1135 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 7 of 17 (504287)
03-26-2009 10:56 AM
Reply to: Message 6 by Dr Jack
03-25-2009 10:49 AM


Thanks for this, but do you know anywhere the article is available public access?

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003


Message 8 of 17 (504288)
03-26-2009 10:57 AM
Reply to: Message 7 by caffeine
03-26-2009 10:56 AM


Um... when I click on the link I gave I get the full text of the paper?

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 Message 7 by caffeine, posted 03-26-2009 10:56 AM caffeine has replied

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 Message 9 by caffeine, posted 03-26-2009 11:10 AM Dr Jack has replied

  
caffeine
Member (Idle past 1135 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 9 of 17 (504289)
03-26-2009 11:10 AM
Reply to: Message 8 by Dr Jack
03-26-2009 10:57 AM


You need an account with Interscience to access it. Your browser must just be set to automatically log you in.

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 Message 8 by Dr Jack, posted 03-26-2009 10:57 AM Dr Jack has replied

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003


Message 10 of 17 (504291)
03-26-2009 11:32 AM
Reply to: Message 9 by caffeine
03-26-2009 11:10 AM


No, it's not. I'm not showing as logged in, and I can access it fine from another browser.
Perhaps you could try starting from the home page of Wiley Interscience and navigating through to the article. It's in the April 2009 issue of Cell Motility and the Cytoskeleton, on pages 215—219. It's called 'The Evolution of the Cilium and the Eukaryotic Cell'. If that doesn't work, I'm afraid I'm stumped because, as far as I know, I don't have any special access rights to it?
Edited by Mr Jack, : No reason given.

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RAZD
Member (Idle past 1515 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 11 of 17 (504309)
03-26-2009 6:51 PM
Reply to: Message 10 by Dr Jack
03-26-2009 11:32 AM


I get the sign up page too.

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Modulous
Member (Idle past 95 days)
Posts: 7801
From: Manchester, UK
Joined: 05-01-2005


Message 12 of 17 (504348)
03-27-2009 12:13 PM
Reply to: Message 5 by caffeine
12-30-2008 7:42 AM


I forget exactly what Dawkins wrote, and I don't have the book here to check, but he didn't discuss the matter in any detail at all. He basically just wrote that eukaryotes were formed by bacteria living together in colonies. I think my ire was raised a bit just by the way he'd declared as brute fact what I understood to still be controversial and debated.
quote:
Bacteria of several different kinds got together, more than a thousand million years ago, to form the 'eucaryotic cell'. This is our kind of cell, with a nucleus and other complicated internal parts, many of them put together from intricately folded internal membranes, like the mitochondria...The euaryotic cell is now seen as derived from a colony of bacteria. Eucaryotic cells later got together into colonies. Volvox are modern creatures...But it is possible that they represent the kind of thing that went on more than a thousand million years ago
I'm assuming this is the passage in question? Hope it helps.

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Saviourmachine
Member (Idle past 3664 days)
Posts: 113
From: Holland
Joined: 01-16-2004


Message 13 of 17 (504648)
04-01-2009 5:59 AM


Genesis of organisms
I build modular, self-organizing, docking robots (or actually their control architecture). From that point of view I am really interested in the computational power of an organism versus swarm organization of robotic modules. I write about it on my blog, entry 14 and 15. I like also the work of Tony Prescott for example about the application of primitive nervous systems on robots. Do you guys now what the advantages of a (multi-cellular) organism are? Why should I want to have a robot organism rather than a robot swarm? Are any of you interested in defining a scenario in which organisms and swarms emerge?

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straightree
Member (Idle past 4861 days)
Posts: 57
From: Near Olot, Spain
Joined: 09-26-2008


Message 14 of 17 (504846)
04-03-2009 3:35 PM
Reply to: Message 13 by Saviourmachine
04-01-2009 5:59 AM


Re: Genesis of organisms
I do not know what a swarm robot is, but as for multicellular organisms, the advantage is specialization of functions. The unicellular being has to make all functions, feed, reproduce..., by itself. In colonies first, and later in pluricellular beings, there is specialization, giving rise to tissues, and full organs.

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straightree
Member (Idle past 4861 days)
Posts: 57
From: Near Olot, Spain
Joined: 09-26-2008


Message 15 of 17 (504884)
04-04-2009 3:32 AM
Reply to: Message 4 by pangor
12-24-2008 4:26 AM


Climbing Mount Improbable
Hi pangor,
Your message is quite old, so I do not know if you are still interested on the subject. I have a copy of the book, and read it some years ago. It is a very interesting and well written book, very didactic. Only thing I do not like is that Dawkins is very belligerent against religion, but for scientific popularizing, it is excellent. If you give me some address, I can send you the book.

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