Can anyone provide a viable stable source of cytosine for RNA replication with prebiotic life?
Thanks.
Well cytosine is required to implement RNA replication. So, if there is no viable source of cytosine, then life could have never got off the ground on this planet.
I don't think that there is a stable source of cytosine in isolation. I guess that proves that life does not exist on earth.
In DNA and RNA, cytosine is paired with guanine. However, it is inherently unstable, and can change into uracil (spontaneous deamination). This can lead to a point mutation if not repaired by the DNA repair enzymes such as uracil glycosylase, which cleaves a uracil in DNA.
The lack of a stable source of cytosine suggests that protein based pre-life came before RNA.
from Wikipedia; (cytosine)
Before the repair enzymes were available, back in the day, cytosine deamination into uracil, would have caused all the genes on the RNA, with cytosine, to become richer in uracil and lighter in cytosine over time. This makes it harder for any genes on the RNA to be permanent.
Does anyone know the gene composition for the repair enzyme, uracil glycosylase, to see if these genes contains cytosine. If so, how does the cytosine in these genes remain stable to make repair enzymes, before there are repair enzymes?
The conceptual problem with pre-repair enzyme RNA replicators, is that the deamination drift of cytosine to uracil could result in useful gene for one replication cycle. But the next time the RNA divides, continuing drift makes the same genes different, causing loss of what had been gained. What that would do is add more protein variety to the cytoplasm through a spontaneous deamination version of epi-genetics.
The analysis I presented is more appropriate, further down the time-line of life, after pre-cells become viable, but before repair enzymes. The genes will spontaneously drift from being richer in cytosine to richer uracil, adding protein variety to the cytoplasm; deamination epi-genetics. Since the chemical reaction is consistent, the protein drift will have a reflected goal in mind; higher and higher uracil mRNA.
Your original question is occurs much earlier in the time-line of life. This does create a problem for the replicator theory. This is not the only problem with the replicator theory. The replicator theory also causes entropy to get lower (nature of a template), whereas nature requires the entropy to increase. The deamination moves in the direction of higher entropy so this is expected as an offset. To fight this, the enzymes have to fight entropy. Starting with only replicators has a second law problem, with deamination reflecting the need for more entropy.
This entropy problem, implicit of bare bone replicators, can be resolved if there is an entropy off-set. This could be done with protein scaffolding appearing first, that supports decomposition or crude metabolic reactions. This will add high levels of entropy to compensate. This consideration would suggest cytosine coming from protein, with the needed protein entropy off-set also leading to synthesis reactions for cytosine.
Can anyone provide a viable stable source of cytosine for RNA replication with prebiotic life?
Thanks.
My best guess is cytosine will appear from protein decomposition reactions, instead of protein template reactions. In the second (very large) figure, notice uracil has the atoms from two peptide links in the ring.
I picture, protein driven decomposition of other protein, increasing the pre-cell entropy, by cleaving bonds. This is not being done in the most efficient way leading toward any goal but higher entropy. The atoms in the active peptide links recombine in new ways. If the cleaved fragments have radicals, they can combine in reverse peptide fashion, with side by side nitrogen. As long as the ring closes this will remain.
The enthalpy of formation of cytosine is about 60 k.joules/mole so this is a favorable reaction.
Here is one avenue. Maybe there is life on earth after all!
Nah, I don't feel like it. Let's just assume there is no life on earth.No. This paper cuts off the RNA pathway. I have no idea why you think it supports it. If you really think it supports the RNA pathway, prove it.
Nah, I don't feel like it. Let's just assume there is no life on earth.
Aw, gee, some folks just won't feed the troll(s).
Define "stable". Then define "provide".Cool. Can you provide a viable stable source of cytosine for RNA replication with prebiotic life?
Define "stable". Then define "provide".
Stable cytosine is defined in this paper.
http://www.pnas.org/content/96/8/4396.full
Provide is something you look up in a dictionary troll.
Pre-biotic means there wouldn't be complex biotic proteins to decay; so one needs to look for a formation method from simpler materials. A good graduate student problem to do a thesis on.