Another Explanation for Multicellular Life 87
DrJay writes "Hot on the heels of Slashdot's coverage of a controversial model for a viral origin of the multi-cellular branch of life, Nature has published an alternative model that has nothing to do with viruses. Ars Technica's science journal has the rundown on the differences between these proposals." From the Ars article: "It's funny that this proposal for the origin of Eukaryotes should hit the popular press at a time where Nature has just published a hypothesis regarding the formation of the nucleus that has nothing to do with viruses, but everything to do with parasites. The parasites in this case are molecular: Type-II introns. These DNA sequences exist in both eukaryotes and bacteria, where they can insert in the middle of genes without causing harm because they can undergo chemical reactions by which they remove themselves from the RNA messages the genes make."
Uh (Score:2, Funny)
Re:Uh (Score:2)
What? This is slashdot. Do you really think we'd actually go out on a Friday night?
Re:Dupe! (Score:2)
If you've got proof it's a dupe, the folks at SETI would like to hear from you.
Re:All we know is that we don't know. (Score:5, Informative)
Eukaryotes are 1 of 3 domains of life in the current popular classification of life. The other 2 domains are Prokaryotes(single cell organisms) and Archaea(these tend to be the thermal vent/volcanic organisms, extremophiles.)
Eukaryotes are characterized by being mostly multicellular organisms(that is made up of more than 1 cell), and those cells have membrane bound organelles(think of little organs but for cells). Eukaryotic cells also have a nucleus which protects and regulates access to the DNA material. In the other domains the DNA is just floating around.
When the cell goes to make proteins, the blueprints are found in the DNA. When a template for a protein needs to be made, it is copied from the DNA, processed and then transported out of the nucleus to be further process into a protein, this template is called mRNA(messenger RNA).
In Eukaryotes you also find what is referred to as "junk DNA". Although this term isn't entirely accurate, this junk DNA is called such because no active proteins are made from the DNA sequences in this region. These non-coding regions are cut out from the template mRNA are called introns. The segements that are kept are called exons.
Basic rundown of some of the concepts the article refers to.
Re:All we know is that we don't know. (Score:1)
introns & junk DNA (Score:2, Informative)
It seems that Introns are considered part of 'junk DNA', but given the fact that in some cases introns play an important part I think this is unfair to introns....
Re:introns & junk DNA (Score:4, Informative)
For more interesting 'proof', see my paper in febuary nature genetics about conserved noncoding regions under selection - one of the strongest signals for selection was seen in intronic regions. We found parts of introns that were under as strong selection as coding regions.
It's nowhere NEAR junk DNA.
Re:introns & junk DNA (Score:1)
But the Wikipedia [wikipedia.org] seems to think so, and some of he post I read also think Introns are ' just junk'. Off course it may turn out that there is no such thing as junk DNA and all this non coding stuff serves a purpose.
Re:introns & junk DNA (Score:2)
Re:introns & junk DNA (Score:1)
Re:All we know is that we don't know. (Score:2)
Re:Laymans terms (Score:2, Informative)
Re:Laymans terms (Score:1)
Re:Laymans terms (Score:2)
Re:Laymans terms (Score:5, Informative)
Central Dogma
So if you follow back up the chain, DNA is responsible for creating protiens which perform biological and chemical functions. DNA->RNA->AminoAcidChain->Protein
http://www.accessexcellence.org/RC/VL/GG/central.
Prokaryote/Eukaryote
Life is classified into two major groups, prokaryotes and eukaryotes. They fall into these two groups based on what kind of cells they have inside them.
Prokaryotic cells are simple, not a lot of really complex organization inside of them. Bacteria like E.coli fall into this group. Prokaryotes can do some cool things with the incorpration of foreign DNA (other cells, viruses, etc.) into their own DNA.
Eukaryotic cells are more complex, they have more "organized" inside them. The biologists call it "membrane bound organelles". Humans have eukaryotic cells.
http://en.wikipedia.org/wiki/Prokaryote [wikipedia.org]
http://en.wikipedia.org/wiki/Eukaryote [wikipedia.org]
Introns/Exons
Introns are what you hear referred to as "Junk DNA". However it's becoming apparent that this is the worst naming possible, as there are theories about it's presence being an activator for other processes which take place during DNA replication.
Exons are the sections of the DNA that are directly tranlated into the coresponding mRNA
Here is a DNA strand, the "E" are exons, and the "o" are introns.
EEEEEEEEEEEEooooooooooooooEEEEEEEEEEEEEEEEooooooo
Now here is the coresponding RNA, the ^ denotes a splice point where introns were removed. (This is what's used to create a given protein)
EEEEEEEEEEEE^EEEEEEEEEEEEEEEE^EEEEEEEEEE
http://en.wikipedia.org/wiki/Intron [wikipedia.org]
http://en.wikipedia.org/wiki/Exon [wikipedia.org]
Summary
So basically this article is saying that there are parasitic sequences of non-coding DNA which survive simply because they are in the DNA of a sequence which survived replication. But in eukaryotes, these "non coding" secions starting causing havoc in the cell and cause altered function.
Here is a analogy, albeit a tasteless one:
Imagine a room full of mimes (yes, mimes). Normally, they would sit there, pretending to be a box and not saying a word. Now imagine there is one mime that snuck a baseball bat into the room and started clubbing all of the other mimes in the knees. What do you think is gonna happen? Yep, they are no longer mimes.. they are now just angry dudes with white face paint on screaming at the top of their lungs.
Cells with DNA in them = Room of mimes
Parasite = baseball bat equiped mime
Havoc = clubbing knees
Altered Function = screaming instead of being mime-like
http://en.wikipedia.org/wiki/Mime_artist [wikipedia.org]
Biologists, feel free to correct any gross errors here. However, I stand by my analogy.
-s
Re:Laymans terms (Score:4, Informative)
Re:Laymans terms (Score:1)
Re:Laymans terms (Score:2, Funny)
Is that you, Lord Havelock Vetinari, Patrician of Ankh-Morpork?
History, not science (Score:2)
Towards the end of the 19th century the main French and British linguistic societies banned any further papers on the origins of langiage because unprovable spec
Re:History, not science (Score:3, Informative)
Re:History, not science (Score:2)
But that would only tell us one way that life might form: in a test tube in some nanotech-era laboratory. That's probably not how it actually got started on Earth (although YMMV, especially if you're from Kansas.)
However, I don't think it's a lost cause. The fossil record won't tell us anything here, but evidence may well come from the details of the
Re:History, not science (Score:2)
Still, it could be something like an incredibly precisely-controlled Miller-Urey experiment, rather than an direct fabrication of life (though that could very well be harder to do).
Re:History, not science (Score:2)
Re:History, not science (Score:2)
However, they can no doubt rule out a lot of ways that might help get closer to the truth of what actually happened.
Re:History, not science (Score:2)
True, but what they can do is illustrate to those that think there is only one (magic, devine) just-add-water explanation that they're simply, demostrably incorrect.
Re:History, not science (Score:2)
Um, if someone believes that life needs an intelligent designer to start, and you intelligently design a device which creates conditions where life can start and then turn it on and watch lifeforms come to be, how have you disproven the belief ?-)
Re:History, not science (Score:1)
you wouldnt be intelligently designing multicellular life. you would putting some single celled organisms in a particular environment and waiting for spontaneous evolution to multicelled organisms.
if that environment was one that can be shown to have occured naturally in the dim and distant past, you have demonstrated a convincing mechanism whereby single cells could have evolved into multi
Re:History, not science (Score:2)
Sure we can. We just need to bring up a bunch of people without ever talking to them, and watch them growl to each other. Of course it takes a pretty monstrous mindset to conduct this kind of experiment, but since the world seems headed towards another era of fascism, it is just a matter of time.
Re:History, not science (Score:1, Insightful)
Wrong. The evidence is all around is in the branches of life existing today. The challenge to us is how to best interpret it the evidence of our biological past.
It' wrong to say that science cannot make claims about past events. We can not only say definitely, for instance, that speciation occurs and that different species have common ancestors. Nowadays w
Re:History, not science (Score:2)
I never said any such thing. But I don't think we can make accurate claims about a specific event that happened a few billion years ago - even with the wealth of genetic evidence we have today. The genomes we see today are like a palimpsest - they're been edited again and again through evolution. There's no reason to believe that there is any readable sign of the first cellular or multicellular organisms. Of course we can accurately order
Re:History, not science (Score:2)
Well, maybe, maybe not.
But one thing is certain: If you refuse to speculate, hypothesize, or test ideas, then it will certainly always be beyond your reach.
And if it turns out not beyond our reach, someone other than you will solve the puzzle.
The history of sc
Re:History, not science (Score:1)
But if you look at insects that have been trapped in amber, that some say are 100 million years old. These don't look very much different from today's variety of the very same species. Is that not a strike against this "empirically observable rates of genetic dr
Re:History, not science (Score:1)
Re:History, not science (Score:1)
Re:History, not science (Score:2)
Re:History, not science (Score:1)
If they couldn't separate idle speculation from well founded hypotheses, they weren't very good academics.
sorry--you're all wrong (Score:2)
How do you know it can't be repeated in a lab? In fact, there is increasing experimental evidence that the steps that lead to life are not a unique accident, but repeatable.
(Not that repatability in a lab is a necessary or sufficient condition for something to be scientific anyway.)
It seems to me that it's a little futile to speculate on how cellular and multicellu
Re:History, not science (Score:2)
No, speculation -- coupled with observation and experiment -- is always useful. Even if we'll never know (without a time machine) how life did arise on Earth, knowing possible mechanisms helps both our understanding of biology as a whole as well as provides insights when looking for life elsewhere in the Universe.
Indeed, it's possible that life arose several tim
Re:History, not science (Score:2, Insightful)
Re:History, not science (Score:1)
The Red Queen. (Score:5, Interesting)
Anyone remotely interested in this discussion who has not yet read Matt Ridley's The Red Queen [amazon.com] should try to grab a copy from their library.
More info on the Red Queen Hypothesis [wikipedia.org] at wikipedia.
Nahh... (Score:4, Funny)
What the hell? (Score:2)
Re:What the hell? (Score:2)
It blew my mind, because we always filter out thin
huh? (Score:1)
Re:huh? (Score:4, Informative)
Sure, there are things that are colonies of prokaryotic cells, but those are recognized as organisms at the individual cell level, not the colony level. Do you have a counterexample?
Of course, there are plenty of single-celled eukaryotic organisms, and I think that's what the article is really talking about.
Reflections (Score:2)
Am I too much of a geek, or did this remind anyone else of a rather similar situation with source code, Ken Thompson's fascinating 'Reflections on Trusting Trust [acm.org]'?
I'm a noob. How do I read this article? (Score:2, Interesting)
Re:I'm a noob. How do I read this article? (Score:2, Funny)
Re:I'm a noob. How do I read this article? (Score:1, Informative)
Re:I'm a noob. How do I read this article? (Score:2, Informative)
Re:I'm a noob. How do I read this article? (Score:2)
Re:I'm a noob. How do I read this article? (Score:1)
Things like this... (Score:1)
So much misinformation (Score:5, Informative)
Or search Wikipedia, google, etc.
1. "Most of the DNA in the cell is wrapped in a fat and protein membrane."
Most of the DNA in "all" three kingdoms are wrapped up in proteins. In eukaryotes there is a membrane that surrounds the entire set of chromosomes (except during cell division) called the nuclear membrane. Chloroplasts and mitochondria are also surrounded by membranes. All membranes have proteins in them. In Prokaryotes, the entire cell is surrounded by at least one membrane, and the DNA is inside of this in the cytoplasm. It does not float freely. In prokaryotes, most chromosomes are circular (but not always) and most organisms have one chromosomes (but not always). In eukaryotes, most organisms have multiple linear chromosomes.
NB: Membranes are comprised of lipids and proteins and in some cases other molecules like cholesterol. Lipids are also known as "fat" and there are many different types.
2. Central dogma/transcription/translation.
In prokaryotes, transcription (copying DNA to mRNA) and translation (translating the RNA to create polypeptide (protein) chains, done by the ribosome) are coupled. In eukaryotes it is uncoupled as the RNA has to be transported out of the nucleus through the nuclear pore, where the mRNA is then translated by ribosomes in the cytoplasm, or by ribosomes attached to the ER and exported.
3. Prokaryote/Eukaryote introns
Introns are not eukaryotic-specific. All three branches of life have introns, however, they are far rarer in the archaea and bacteria (especially rare). Some introns can self-splice (remove themselves), while others do not. Lots of different "types" of DNA can move themselves around, insertion sequences, transposons, phages, viruses, conjugative DNA, etc. This movement of DNA is a driving force in evolution itself, not merely in a host organism protecting itself from invasive DNA, but in the evolution of novel protein functions.
4. Single/multicellular
There are single-celled eukaryotes (yeast cells) and there are prokaryotes that form developmentally specialized conglomerations of cells (biofilms, cyanobacterial chains, mycelial hyphae) where some cells are specialized as compared to others. Many prokaryotes can signal to, as well as receive signals from, other cells.
5. Mimivrius
Mimivirus is interesting, but it is an extreme outlier. More work on the full range of virus forms and genome ranges will help in this arena. Some of the metagenomic projects will definitely help in this area. It's like attempting to hypothesize the evolution of mulicellular organisms based on the blue whale.
6. Introns and domains.
Proteins fold into 3D structures to perform functions. The basic unit is a domain, which are units that can fold into a 3D structure themselves and perform some function (basically). Exons and domains are not a 1 to 1 relationship. IMO, intron evolution has a lot more to do with alternative splicing events and regulation in developmental pathways than it does in driving new functions for genes (you can duplicate genes and domains without introns/exons).
7. Membrane evolution.
Membrane compartmentalization is a key step in evolution. Interestingly the prokaryotes (archaea and bacteria) have two different types of lipids, suggesting that in the early stages of this evolutionary step that two pathways were chosen, and both have been maintained since that time. Again, another point in evolution is not that one system is always better than another, but that endpoints are achieved through multiple pathways.
8. Koonin et al., hypothesis.
Their hypothesis is interesting. I haven't read the paper, but I have seen Koonin's seminar from a few months ago. Unfortunately there is so much we don't know yet. His ideas may be skewed towards analyses based simply on comparative genomics and not enough on biochemistry.
slashdot coverage? (Score:2)
Slashdot covers news like David Spade's jacket covers Chris Farley's back.
Re:slashdot coverage? (Score:1)
How life started (intelligent design) (Score:1)
In some years experiments with timemachines will transport living cells back in time to before life was present here on earth.
So, we create life.
Thats intelligent design.
Random, Chance Processes Always Dilatorious (Score:1)