Origin of Life

Originally posted by Retrovirus
That's were the "RNA world" hypothesis fits in.

RNA can both store information (although DNA is better at it) AND catalyze reactions (although proteins are better at it).

http://en.wikipedia.org/wiki/RNA_world_hypothesis

Now it gets interesting. I agree, not all enzymes are proteins. BUT!!! But, can RNA catalyse self-replication? Has it been shown? Will it ever been shown?

Originally posted by znsho
Now it gets interesting. I agree, not all enzymes are proteins. BUT!!! But, can RNA catalyse self-replication? Has it been shown? Will it ever been shown?

c'mmon, don't forget ribozyme from a good old mol. biol. textbook. RNA can get interesting tertiary structures, why doesn't it also catalyses it's replication? A plausible theory that is.

Some are missing the point. DNA has the quality of self replication. On point, it is true that the enzymes provide a type of chemical engineering that facilitates the chemistry. RNA certainly "transcribes" the DNA and "transfers" the information.

Originally posted by coquette
Some are missing the point. DNA has the quality of self replication. On point, it is true that the enzymes provide a type of chemical engineering that facilitates the chemistry. RNA certainly "transcribes" the DNA and "transfers" the information.

DNA and RNA aren't same.

DNA has no catalytic activity.

Originally posted by znsho
Now it gets interesting. I agree, not all enzymes are proteins. BUT!!! But, can RNA catalyse self-replication? Has it been shown? Will it ever been shown?

http://www-ssrl.slac.stanford.edu/research/highlights_archive/ligase.html
possibly...
also look up polycyclic aromatic hydrocarbons.

Thought I'd post a few bookmarks I picked up during my uni course, they might be of interest...
http://en.wikipedia.org/wiki/PAH_world_hypothesis

http://www.sciam.com/article.cfm?chanID=sa004&articleID=9952573C-E7F2-99DF-32F2928046329479

http://library.thinkquest.org/C003763/index.php?page=exobio02

http://www.sciam.com/article.cfm?chanID=sa006&articleID=00073A97-5745-1359-94FF83414B7F0000&pageNumber=4&catID=2

Another one to Retrovirus is that some must have the ability to form/break double bonds easily, which is why silicone isn't a building

In this vein, I heard recently that silicon is a more abundant element on earth than even carbon. If so, why did silicon-based life not develop instead of (or alongside) carbon-based forms?

Originally posted by PinkFloyd
In this vein, I heard recently that silicon is a more abundant element on earth than even carbon. If so, why did silicon-based life not develop instead of (or alongside) carbon-based forms?

The C-H, C-N and C-O bonds are far more energetically stable than Si equivalent. Si based amino acid compounds do not form as the structures are chemically unstable. Hence a huge area of chemistry possible with carbon is not stable with Si

Originally posted by PinkFloyd
In this vein, I heard recently that silicon is a more abundant element on earth than even carbon. If so, why did silicon-based life not develop instead of (or alongside) carbon-based forms?

Carbon happened to have a right size, forming double or triple covalent bonds with O, N, H notably. The feature of carbon atom allows molecules to form complex interaction within or in between molecules via distributed electrons in certain manners.

Apparently, silicon is too large to manage that sort of trickeries.

http://en.wikipedia.org/wiki/Alternative_biochemistry

Originally posted by kyue
Having nucleic acids only does not mean that "it" is capable of reproduction on the earth.
(e.g. viruses cannot replicate independently without infecting a host cell to utilise its machinery)

Nucleic acids are just like a set of instructions. DNA is a master copy and RNA is a print-out for a short-term.

Don't tell me off for stating obvious...........

That's only because life has modified the environment and in addition would actively compete with any nucleic acids undergoing abiogenesis.

Originally posted by PinkFloyd
In this vein, I heard recently that silicon is a more abundant element on earth than even carbon. If so, why did silicon-based life not develop instead of (or alongside) carbon-based forms?

it's a temperature thing. think granite. on the other hand, on a planet like mercury (way hotter), silicon life might just be the thing.

Originally posted by PinkFloyd
In this vein, I heard recently that silicon is a more abundant element on earth than even carbon. If so, why did silicon-based life not develop instead of (or alongside) carbon-based forms?

We will have to see what the future brings on that one.

It may be that we are the parallel of the initial minerals that
brought about Carbon based life.

Originally posted by kyue
c'mmon, don't forget ribozyme from a good old mol. biol. textbook. RNA can get interesting tertiary structures, why doesn't it also catalyses it's replication? A plausible theory that is.

Meow!

Originally posted by serigado
All life that ever existed on earth seems to be RNA-DNA based. This definitely evidences an original life from which all life forms evolved.

That is just so wrong.
1. We define 'life' too narrowly, and essentially mean 'cellular life'.
2. If we are to talk about self replicating systems then there or other known ones such as virus', prions and even parts of the cell considered individually.
3. We do not know, nor even have good reason to think, that RNA-DNA based cellular life is the only form on the planet. We have not even identified half of the single celled life forms, if there is a form that is not overly common that is not cellular or does not share a common ancestor with us, we may never even know about it. Has anyone even looked at deep see mud under a microscope?

I imagine early cells were a mixture of both DNA and RNA, broadly speaking
indistuinguishable in respect to todays models.

The question arises, at what point did the disctinction in their functions arise
and why??

I expect it had something to do with the enormous energy required for these
processes.