Metabolism or Replication First?
September 15, 2007 at 3:56 pm #8233
About the origin of life, different scientist holds different opinions. Some argue that metabolism has originated much earlier than replication (not reproduction),but others argue that replication has pridiated metabolism.
In my opinion, metabolism is more ancient than replication.
But what do you think about this?
September 16, 2007 at 12:10 am #76035DarbyParticipant
If you define metabolism as any chemistry involving energy transfer, which seems a fair definition, then reproduction is a subset of metabolism – and it is, isn’t it?
September 17, 2007 at 3:21 pm #76081
In my opinion, replication is not equal to reproduction, although lots of people often confused the two natural phenomenon. Reproduction means something increase their number in approximate way, and replication means a molecule making an exact copy of itself, for example, DNA replication.
I think, in the origin of life process, metabolism has come first, reproduction second. And more and more later, replication has occured. Energy transfering is not a difinition of metabolism. If we think that metabolism is any chemistry involving energy transfer, then our automobiles also have metabolism, and they belong to life, then the differences between life and non-life absolutely vanished. Do you have different ideas?
September 17, 2007 at 4:07 pm #76082mithParticipant
I don’t think that’s a valid argument, because life is defined as having metabolism, but having metabolism is not the only qualifier for life.
September 17, 2007 at 9:26 pm #76092DarbyParticipant
But this is abiogenesis, well before entities that would be considered broadly alive – just molecules and molecular complexes, before even protocells. The molecules needed to be able to self-organize, which is a type of metabolism, and reproduce, which matches the "replication" described above, and evolve, but the rest of the requirements of currently-living systems come later.
September 23, 2007 at 2:37 pm #76223
We have no evidence to assume that the first living forms on earth possess all characteristics of modern creatures. They only have a kind or several kinds of them. So I can say that metabolism and replication have not originated at the same time.
September 24, 2007 at 3:31 pm #76268Roland PohlmeyerParticipant
I guess this question brings us to examine closer how we define life itself. We are talking about processes that occurred more than a billion of years ago, and we have little evidence of how and in what order these events took place. Robert Shapiro recently wrote a very interesting article on the metabolism first theory in Scientific American, but I seem to have a different definition of what makes life life than he does.
All I can say is that life is the coming together of both metabolism and material that can store and replicate information. As with so many processes in life, evolution seems to get most interesting when cooperative strategies produce results.
October 8, 2007 at 4:07 pm #76715AzedenkaeParticipant
Well, I believe that they evolved at the same time. This is because life, defined by many, involves both a form of replication and metabolism. And as such when life evolved, it must have contained both at once, possibly from a combination of factors, whether or not a form replicated first, then started to metabolize or the opposite, it is the moment that the other appears that it can be sort of a primitive life form. As such… yeah…
Then again, that’s just me.
October 23, 2007 at 4:31 pm #77142adamd164Participant
If we take replication to mean a living entity making a copy of itself, then this, to me, is life, and so must necessarily have been around since the beginning, with metabolism coming later, as organisms developed.
October 24, 2007 at 8:25 pm #77184mithParticipantquote adamd164:
Ah, but how did this living entity come to be? Was it from replication?
October 26, 2007 at 12:38 am #77210AstusAleatorParticipant
Ok so we should establish that replication is on the molecular level, before cellular.
Life evolved as something like nucleic acids inside a lipid bubble, or perhaps even more basic than that.
In the most "primitive" forms, these nucleic acids would have to have chanced upon a way to replicate themselves, or evolution would never have occured.
The problem is that for this to occur, there was probably some sort of energy input required. The question then becomes, was this energy input in the form of some sort of metabolic process, or just environmental (ie sun, temperature, electric current)
When I think of metabolism, even in the tiniest most basic of creatures, I think of pathways that break down molecules and harness energy usually in a carrier molecule. I can’t think of any more basic way for metabolism to occur… perhaps someone can fill me in if there is.
So resorting to Occams Razor would lead me to believe that it would have been simpler for initial proto-life to be composed of self replicating molecules that were dependent on environmental energy inputs (kinetic, etc). Therefore, replication before metabolism.
October 26, 2007 at 6:25 pm #77231
November 4, 2007 at 9:47 pm #77469AstusAleatorParticipant
That’s a very interesting read. It’s good to have a source to run back to when I forget some details (which I do all the time).
Also, as far as I’ve read, it supports my position that replication came before metabolism :).
December 4, 2007 at 4:01 pm #78922norneratorParticipant
I would think that self-replication would come first, before "metabolism" if we are talking about metabolism in the sense of energy production and storage and not the more general sense of all the chemical reactions happening.
I imagine that self-replicating molecules had been around for some time. Replicating slowly. Although considering these are very basic chemicals we are talking about, I would assume that their selectivity for replication would have been quite low, and so the "daughter" molecules may have not always been exact replications of the first. Eventually one of these molecules was created in that way, and this molecule perhaps allowed some energy to be stored within it (perhaps a phosphoanhydride bond) so that the replication process was not completely dependent on external energy but had energy stored up from the environment in this form. Obviously the molecules that could reproduce easier, reproduced in the largest of numbers. More changes happened via poor selectivity in these molecules that eventually allowed for a more complex system of metabolism. Then over billions of years simple metabolism systems grew off of one another, until we reach today when many organisms like EColi, can produce any molecule they need from very simple starting materials, like CO2, H2O and Nitrogen.
If the ability to produce and store energy comes first, not replication, how can the information about the system of energy storage be "passed" on to molecules that do self replicate?
Perhaps the only other alternative I can see being possible is if both processes started out as separate systems.
Perhaps a system of molecules interacting with a hot ocean vent would pick up heat energy, convert it to chemical energy, and self replicating molecules arose due to the abundant chemical energy. Because there is no membrane to hold this system together, any sort of shock to the system would wash this system away.
Once the self-replicating molecules were dispersed away from the primitive metabolism system the ones that were best able at storing and harnessing energy were best able to replicate and therefore the most successful continued perpetuating their information.
Of course all of this is complete conjecture, unless we find out the the universe in infinitely entangled with itself, we will never be able to know exactly how it happened. We can only discuss possible ways that it could have happened, in which in reality, there are in infinite number of ways "life" could form. Life is simply a measure of complexity within a system.
December 4, 2007 at 4:35 pm #78925woolleyyParticipantquote nornerator:
I’d call this myth busted.
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