Reading biochem the other day, I noticed it talked about DNA lesions/mutations but didn’t mention those in RNA. What, do they just not occur in RNA? Or are they less of a problem, for some reason that I’m stupidly overlooking?
And a specific question: OK, so cytosine deaminates to uracil in DNA, but it usually gets fixed. My book says this deamination is probably the reason DNA uses thymine instead of uracil, because if Cs deaminated to Us all the time and DNA repair enzymes didn’t recognize them as foreign, we’d have a lot more mutations, and our genome would be much less stable. But there are cytosines in RNA, right, so how come deamination in those cytosines doesn’t royally screw up our transcripts?
These might be dumb questions…it’s been a while since I’ve cracked the ol’ genetics book.
Well, working off my Introduction to Bio and Microbiology knowledge, so take this with a grain of salt.
A transcript of RNA is usually only around for a little while. And that RNA doesn’t serve as a template for more RNA. So there’s a limited, temporary number of proteins that can be screwed up. I don’t know how long it takes cytosine to deanimate, but it take longer than the life of an RNA strand.
Incidentally, about one of every ten thousand RNA nucleotides is erroneous. DNA’s rate of error is one in several billion because it has failsafe enzymes.
I think mutations can happen anywhere. I don’t see why not. I However, I think they only/mostly happen during transfer (synthesis, transcription, translation).
Well your body probably doesn’t worry about RNA mutations too much since the half life of mRNA is minutes, sometimes seconds, so the mRNA isn’t around long enough to a) form dimers/deaminate/etc and b) produce enough mutant protein to cause considerable damage. On top of that, your DNA looks like a Christmas Tree with dozens of little ribosomes attached synthesizing many mRNAs from the same template, so a mistake in one or two of those won’t have a huge impact on the cell.
Thirdly, the RNA will not be passed on to future cell generations (as Super Gnat noted above), so while RNA damage might effect a cell slightly, it won’t usually effect natural selection (of course cells with TOO many RNA mutations would have been selected out millions of years ago, possibly ones which kept mRNA around for a long time and reused one strand over and over for translation?).
Fourthly, an mRNA mutation isn’t necessarily terrible since it probably won’t be something drastic like a frameshift. You’ve got a 33% chance the mutation is in the wobble position meaning it will have almost zero effect on the protein, and even if the mutation is translated the odds of it being in the active site or majorly important to the protein are low. If it is in the active site the cell will just make more protein (hopefully unmutated this time).
Your cells also have mechanisms to check for proper protein folding via glycosylation. If an RNA mutation effects a cell so greatly that folding is an issue the protein will go straight to the proteosome for degredation.