Submitted by kappusha t3_1036d04 in askscience
SignalDifficult5061 t1_j2y8xax wrote
It varies considerably for a number of reasons.
Transcript lifetime is generally regulated directly by degradation in a time dependent manner. There are regulated in many others ways as well including miRNAs, and probably at least half a dozen other things.
According to the below example the median half-life of a transcript was 7 hours, with a few mRNAs under an hour. This may be very different than for bacteria, or various cell types etc.
How many proteins are made per transcript before degradation is also liable to be very different for reasons like, for example, codon usage (rarer codons tend to have smaller tRNA pools) so it will take longer to translate and thus there will be fewer proteins, and any number of other things.
Database for mRNA half-life of 19 977 genes obtained by DNA microarray analysis of pluripotent and differentiating mouse embryonic stem cells
kappusha OP t1_j2ydgg9 wrote
So next question is how many times per hour mRNA transcript gets translated on average?
SignalDifficult5061 t1_j2ynm86 wrote
I would tend to think that has a worse chance at a useful and glib answer (although you may find some). For anything practical, that rate might not be super informative about what is going on.
It is harder to study because of differences in protein degradation rates and other things. High absolute numbers of a protein made per hour with a high decay rate can have the same ratio as a slow synthesis and slow degradation rate protein, There are a number of other technical challenges. Although there are certainly rates known for some individual mRNAs, and have been for some time, it is harder to look at that on the whole genome
That being said, the paper below suggests one to millions per generation (Figure S1 supplemental), which they define as a minimum of about 21.5 minutes (varies substantially).
The paper below is an E.coli example. It may very quite a bit in other organisms and cell types in multicellular organisms at least. life stage etc.
"Quantifying Absolute Protein Synthesis Rates Reveals Principles Underlying Allocation of Cellular Resources" https://www.sciencedirect.com/science/article/pii/S0092867414002323
SignalDifficult5061 t1_j2yt44u wrote
Interestingly, there are some very weird things that could happen with that rate.
An extreme example I know of is Xenopus oocyte maturation. Oocyte maturation goes through a number of steps, in one of those the oocyte basically hoards a whole bunch of mRNA but doesn't do much with it (for like days), then at the next stage it makes a whole lot of protein but little mRNA.
So in this (somewhat extreme) example calculating the rate of proteins made per transcript is going to yield very different answers, and is also going to obscure what is really going on in the cell.
This is an extreme example, but I'm sure you can see the difficulties.
kappusha OP t1_j30g0lj wrote
>That being said, the paper below suggests one to millions per generation (Figure S1 supplemental), which they define as a minimum of about 21.5 minutes (varies substantially).
Wait does it mean 10^6/(21,5*60)≈ 775 translations per second for one mRNA in e.coli on average ? Or am I confused?
SignalDifficult5061 t1_j35uei8 wrote
That is how I read it, but I really like bourbon. like a lot. I like bourbon.
kappusha OP t1_j35yicq wrote
it just sounds physically impossible
SignalDifficult5061 t1_j3619jj wrote
Yeah, I thought so too. Then again, there are some enzymes that somehow outperform the theoretical maximum diffusion constant. Something about formate as a substrate.
I'm terrified if I talk about this some jerkwad will make some association with a vaccine or aquarium cleaner, and I don't like responsibility.
[deleted] t1_j3kq6xr wrote
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[deleted] t1_j3g5d32 wrote
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[deleted] t1_j3fg2bs wrote
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kappusha OP t1_j3fvtip wrote
Is there any way we can find out it? Like I don't know binding GFP to ribosomes and setting this up so complex will emit light if it translated one mRNA?
Aus_scientist t1_j4upg4e wrote
Polysome profiling can give us an indication of translation kinetics. Basically, a transcript can have multiple ribosomes actively translating on it at once - so measuring this. Pairing this info with transcriptomic info you can get the rate of translation. And then knowing the transcript's degradation kinetics can give you an estimate.
[deleted] t1_j30v3vo wrote
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CrateDane t1_j30vjno wrote
> > > > > How many proteins are made per transcript before degradation is also liable to be very different for reasons like, for example, codon usage (rarer codons tend to have smaller tRNA pools) so it will take longer to translate and thus there will be fewer proteins, and any number of other things.
On that note, codon optimality also influences the half-life of mRNAs.
[deleted] t1_j3607cu wrote
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