Discussion of all aspects of biological molecules, biochemical processes and laboratory procedures in the field.
Thu Dec 15, 2011 4:07 pm
I find it interesting that all life on earth, aside from RNA viruses, use DNA. I've seen video on how helicase and ribosomes work together to copy DNA sequences (to RNA) with helicase then recreate them using ribosomes. Does this process work the same way in the simplest life forms? Bacteria and other unicellular life that reproduce through mitosis, for example?
Thu Dec 15, 2011 4:21 pm
Thu Dec 15, 2011 4:25 pm
So if life sprang out of nothing, which came first? The helicase or the ribosome? I assume the code for creating both of these machines comes from DNA which needs both helicase and ribosomes to function...
Thu Dec 15, 2011 5:38 pm
We don't have direct evidence from which we can answer that question. We do have some current hypotheses. Look into the "RNA world" topic (try Googling that term). Here's one the easy way: http://en.wikipedia.org/wiki/RNA_world_hypothesis
Mon May 21, 2012 4:54 pm
Thanks for the information. I've done some research and I'm still having a hard time making the connection.
Discounting the fact that DNA as a code base (logical) is structured information, and therefore cannot self-assemble, nucleotides, which are the "bits" that make up the code (physical) also have to assembled/synthesized.
The biggest problem is still how to make the jump from RNA to DNA. Helicase needs ATP, which means mitochondria had to come first. Mitochondria only occurs in eukaryotes which are DNA based. RNA based "creatures", such as viruses, don't have mitochondria.
Am I missing something?
Mon May 21, 2012 5:32 pm
ATP does not come only from mitochondria. The RNA could work as template for first proteins and after some long time it could be replaced with more stable DNA.
Tue May 22, 2012 11:53 am
I didn't realize that there were other biological sources for ATP. Please explain that further, if you don't mind. I'm most interested in how they would have been involved in the evolution of RNA to the fully functioning DNA model. How/where would they have been used as RNA was evolving?
I'm still also having trouble digesting how you get from RNA to the fully functioning DNA process - translation and transcription are both required, and each of those processes require multiple components working together. Without all of those parts doing their thing, the critter dies and evolution starts over from scratch.
Tue May 22, 2012 12:55 pm
It doesn't die as long as it is alive and able to replicate.
Tue May 22, 2012 2:13 pm
Is that all you can offer?
Tue May 22, 2012 8:15 pm
Gene expression did not evolve in eukaryotes, they are fairly recent on the geological time scale, so mitochondria are irrelevant to that evolution. Prokaryotes have many metabolic tricks to generate ATP. Glycolosis with fermentation is one possible method. There are methods for generation of ATP from light and from redox of environmental chemicals.
You will likely not find a satisfactory explanation of the early evolution of gene expression and metabolism. Without physical evidence (fossils, etc.) descriptions of early evolution are so far speculative. The earliest fossil evidence of life is bacterial, and key parts of the processes of gene expression and metabolism may have developed acellularly (though again, we have no physical evidence of those very early stages).
Wed May 23, 2012 5:09 pm
Thanks for the info. I should have realized that prokaryotes would have a different mechanism. After reading further on ATP itself, I'm still stuck at the same point. The RNA world theory would have to include a way for evolution to create both ATP as an energy currency and the mechanisms to create ATP itself.
As there is no reason for ATP to even exist until you get to the cellular level, from where/what would it have evolved? ATP seems pretty specific in its functionality - if it didn't exist in its final form when the first cell did, the cell would have died.
I don't need physical evidence at the moment. Just a logical explanation.
Wed May 23, 2012 5:12 pm
Again, it can just go on as it is, it doesn't have to die.
What is the RNA composed of?