The Chicken & Egg Story

[cowboy]

This is something like the chicken and egg story, but it involves DNA. We know that DNA encodes for proteins and proteins are needed for the transcription of DNA. So, which one comes first...DNA or proteins? DNA cannot be transcribed into mRNA (and later translated into proteins) without proteins (RNA polymerases), and proteins cannot be formed without DNA? So, how did the first DNA produce the first protein? :confused:

[YT2095]

and proteins cannot be formed without DNA?

 

says Who?

 

also isn`t RNA the bare minimum required for "life"?

[cowboy]

Sorry, I mean DNA/RNA...

 

But RNA needs other proteins to be translated into proteins as well?

[YT2095]

so in effect you`re really only questioning the origin of the Ribosome?

[cowboy]

Hmm...is ribosome a protein? I mean any other proteins required for translation, for eg initiation factors, etc

 

I don't know, man... my question sounds a bit stupid.. lol

[YT2095]

Ribosomes Build proteins if I rem correctly (it`s been a long time).

 

and no your post/question isn`t Stupid at all, it`s a good and valid question

[Mokele]

The current major theory on the origin of life if the "RNA world". Unlike DNA, RNA is capable of catalyzing reactions like proteins do, and unlike proteins, RNA can easily store information. We've already made "ribozymes" which can do this, and now all we need is one that can self-replicate. It's thought that the original RNA cells eventually moved over to proteins for reaction control and DNA for info storage, leaving RNA with a much reduced role, and only in the ribosome, where proteins are assembled, does it still catalyze reactions.

 

Mokele

[cowboy]

The current major theory on the origin of life if the "RNA world". Unlike DNA, RNA is capable of catalyzing reactions like proteins do, and unlike proteins, RNA can easily store information. We've already made "ribozymes" which can do this, and now all we need is one that can self-replicate. It's thought that the original RNA cells eventually moved over to proteins for reaction control and DNA for info storage, leaving RNA with a much reduced role, and only in the ribosome, where proteins are assembled, does it still catalyze reactions.

 

Mokele

 

 

Interesting! Thanks for sharing your input... I haven't heard of the RNA world hypothesis before this.

[FreeThinker]

Ribosomes are not proteins, they are made out of RNA (rRNA). RNA has the property where it can act as a catalyst as well as the carrier of information. For example, as Mokele already mentioned, a ribozyme has all the properties of an enzyme. It even requires a substrate (Mg) to be active. This would solve the DNA/Protein problem as RNA can do the job of both! We can imagine a RNA world, where RNA can fold itself into complex shapes and perform the work of enzymes.

 

How did DNA and Proteins come into the picture? It is hard to say. Molecules do not leave fossils. But evidence seems to indicate that RNA arose before DNA. The sugar ribose (In RNA) is quiet easily synthesized in the lab, while deoxyribose (in DNA) requires proteins to be synthesized. What about proteins? I would guess something like the following: natural selection favored the stable RNA molecules. Imagine a scenario where one of these molecules could bond easier with a certain amino acid. Now it would be more stable than its non bonding counter parts. At this time on earth, natural selection would have favored the most stable molecules. As different RNA sequences attracted themselves to different amino acids, some of them begun to merge with one another. This would in turn make them more stable. If, somehow, the amino acids within these merging molecules, managed to bond as well, it would make the molecule more stable still. This could have been the beginning to protein synthesis.

[tyciol]

Questions should only be asked regarding RNA origins since it's accepted evolutionary theory that they preceded DNA. I believe they can encode proteins too, and those proteins would have encoded the first DNA.