Metabolism or Replication First?

[titanman]

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?

[Darby]

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?

[titanman]

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?

[mith]

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.

[Darby]

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.

[titanman]

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.

[Roland Pohlmeyer]

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.

[Azedenkae]

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.

[adamd164]

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.

[mith]

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.

Ah, but how did this living entity come to be? Was it from replication?

[AstusAleator]

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.

[siroma]

I like very much this RNA world hypothesis explanation from MBoC4

http://www.ncbi.nlm.nih.gov/books/bv.fc ... .1119#1124