Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: WylieE on 15/04/2007 04:42:53

Title: Where Does DNA Come From
Post by: WylieE on 15/04/2007 04:42:53

Hi Paul, George, and Seany,

 I thought your "what am I" conversation was very interesting.  I wanted to join in, but by the time I had time- y'all had moved on in the conversation- So I'm starting my own:

So where did DNA come from. . .
The idea is that originally it was an RNA world.  RNA and DNA are very similar- there is only an extra oxygen on RNA sugar that is missing from DNA (and one of the bases is different).  See the extra 'O' in the picture below.

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But this extra oxygen makes a huge difference- it makes RNA more reactive than DNA.  The good thing about being more reactive is that it means that RNA can actually act as an enzyme- in other words it can actually do stuff- it can chop up other RNAs, make more RNAs, even make proteins which are very good enzymes.  As George pointed out, DNA can't do this (as far as I know).  For some reason (and this is a really interesting question- but probably deserves a whole different post) some RNA molecules started making more RNA molecules- and those that were good at it kept going and those that weren't, well you don't see them around anymore.

  Then some RNA molecules started using other molecules in the environment to help them make more copies of themselves- eventually making proteins and cells to protect themselves from getting destroyed and to keep the things they made to themselves.  So being reactive allowed RNA molecules to start increasing in number and complexity.  However, being more reactive has its downsides- it also means that RNA is more sensitive to getting destroyed.  Therefore, in comes DNA- DNA is much more stable.  So whenever long term storage is needed DNA is used.  RNA is still used to translate the DNA into proteins and as some enzymes to do many functions in the cell. But when keeping the data intact is really important, DNA is used. 
 
There are still some viruses that only use RNA to store there information- they are subject to high rates of mutation- but then, this has some advantages for a virus.

OK, enough fun. . back to work.
Colleen

Title: Where Does DNA Come From
Post by: DoctorBeaver on 16/04/2007 08:56:14

Colleen - that's really interesting & you explained it very well

Title: Where Does DNA Come From
Post by: another_someone on 16/04/2007 09:23:18

Indeed so - sorry I did not respond yesterday - I was otherwise occupied and did not spend much time on the site yesterday.

I was not aware that RNA could act as an enzyme.

One question must still be whether RNA is indeed capable of reproducing independently of any proteins, and whether it can survive without some sort of cell environment to protect it?

Beyond that, the question must be not only whether one can have an RNA virus, but whether one can have an RNA bacteria (or proto bacteria)?

Title: Where Does DNA Come From
Post by: paul.fr on 01/06/2007 21:40:27

Hi Colleen,

I missed you posting this, sorry. I think what you have written does not deserve to be ripped apart with theories and whatever!

so if you don't mind i will restart the conversation in the old topic.
http://www.thenakedscientists.com/forum/index.php?topic=7198.0