# mRNA lifetime? **URL:** \ **Category:** Factual Questions\ **Created:** [December 3, 2020, 4:35pm UTC](https://boards.straightdope.com/t/mrna-lifetime/927127 "2020-12-03T16:35:51Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [December 3, 2020, 4:35pm UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/1 "2020-12-03T16:35:51Z")
Once a ribosome has “read” a piece of mRNA to add an amino acid to a protein that is being constructed, what happens to the mRNA? Is the readout a destructive process, or does the mRNA just sort of “spool out” of the ribosome again in such a way that it can be used again by another ribosome? Textbooks don’t seem very clear on this point. Obviously this has some bearing on recent Covid vaccines, but it’s really a general question. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 3, 2020, 4:53pm UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/2 "2020-12-03T16:53:09Z")
Readout (it’s called _translation_) is not an inherently destructive process. mRNA degradation is carried out by specific enzymes, and the process is regulated as one aspect of the overall process of regulating gene expression - cellular control of how much of a protein is produced and when. Here’s a review of the mechanisms, slightly out of date but it appears to be open access: [https://www.nature.com/articles/nrg3160](https://www.nature.com/articles/nrg3160) ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 3, 2020, 5:00pm UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/3 "2020-12-03T17:00:23Z")
Here’s the [pdf of that paper](http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3351101&blobtype=pdf) if you can’t see it. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [December 4, 2020, 4:34am UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/4 "2020-12-04T04:34:03Z")
Translation of mRNA isn’t a destructive process and, indeed, multiple ribosomes can simultaneously translate the same piece of mRNA. This is called a polysome or polyribosome. Wikipedia: > **[Polysome](https://en.wikipedia.org/wiki/Polysome)** > > Pages for logged out editors learn more > > A polyribosome (or polysome or ergosome) is a group of ribosomes bound to an mRNA molecule like “beads” on a “thread”. It consists of a complex of an mRNA molecule and two or more ribosomes that act to translate mRNA instructions into polypeptides. Originally coined "ergosomes" in 1963, they were further characterized by Jonathan Warner, Paul M. Knopf, and Alex Rich. > Polysomes are formed during the elongation phase when ribosomes and elongation ... Bioninja, including a scanning electromicrograph of some polysomes: > **[Polysomes | BioNinja](https://ib.bioninja.com.au/higher-level/topic-7-nucleic-acids/73-translation/polysomes.html)** > > Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane AND Identification of polysomes in electron micrographs of prokaryotes and eukaryotes ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [December 4, 2020, 4:39am UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/5 "2020-12-04T04:39:59Z")
I should add that Figure A on the above Bioninja site shows polysomes forming on mRNA while it is being transcribed from DNA. This can only happen in prokaryotes (i.e., bacteria) since they don’t have a nucleus. In eukaryotes (i.e., plants, animals, fungi), transcription occurs inside the nucleus then mRNA is transported outside into the cytoplasm where translation occurs. Polysomes can still form regardless. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [December 4, 2020, 4:54am UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/6 "2020-12-04T04:54:39Z")
And to answer the original question, average lifespan of mRNA in E. coli (prokaryote) is about 5 minutes. In yeast (single-celled eukaryote) it’s 20 minutes. In humans (multicellular eukaryote) it’s 600 minutes. > **[» How fast do RNAs and proteins degrade?](http://book.bionumbers.org/how-fast-do-rnas-and-proteins-degrade/)** > > Vignettes that reveal how numbers serve as a sixth sense to understanding our cells ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [December 5, 2020, 4:20pm UTC](https://boards.straightdope.com/t/mrna-lifetime/927127/7 "2020-12-05T16:20:26Z")
Thanks, guys; useful info. I’ve bookmarked several of the links in my “science” folder!