Can mRNA be used by ribosomes more than once? I mean can mRNA be translated more than one time? If not what will happen to it after translation?
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1$\begingroup$ Have you looked for an answer on your own? $\endgroup$– Bryan Krause ♦Dec 30, 2016 at 20:22
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1$\begingroup$ Welcome to SE Biology. Before asking a question we expect you to have done some work yourself. This is a very basic question the answer to which you can find in Wikipedia or in the online editions of textbooks like Berg on NCBI Bookshelf. $\endgroup$– DavidDec 30, 2016 at 21:07
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There are a few cases in translation that I can think of where an mRNA is translated more than once: the closed loop model of mRNA translation, translation reinitiation, and translation by polysomes.
Closed-loop model
Here's an interesting paper to get you started: ncbi
Essentially, the theory is that mRNA can form a closed loop with the 3' end held to the 5' end by various factors. The ribosome assembles near the start, runs through the mRNA, translating the polypeptide sequence, then dissociates at the STOP codon. Since the "end" of the mRNA is near the "start" of the mRNA, the ribosome can reassemble soon after dissociation.
Translation reinitiation
See this.
The ribosome dissociates incompletely at the STOP codon, the small subunit keeps moving on the mRNA, then the large subunit reattaches at a downstream start site. This happens when the mRNA has multiple ORFs.
Polysomes
(See the wikipedia article on Polysomes for more details)
This basically means that you have a ribosome train moving along an mRNA. The same protein is being translated multiple times, but by different ribosomes. One really cool thing about this is that it's actually been observed by electron microscopy!
(source: bioninja.com.au)
To answer the 2nd part of your question... wikipedia
mRNA gets degraded in a process called RNA interference (RNAi). Small interfering RNAs (siRNAs) are also transcribed that are incorporated into a ribonucleoprotein complex (RISC) that has an mRNA cleaving activity. The siRNAs are complementary to segments of mRNAs in order to give specificity to RISC.
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1$\begingroup$ You should not have answered this question but waited until the poster had shown some evidence of effort himself. As it happens your answer is unduly complicated for a novice and incorrect as regards RNA degradation. $\endgroup$– DavidDec 30, 2016 at 23:12
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2$\begingroup$ I agree with everything @David said. I'd also add that translation reinitiation is not "reusing" the mRNA, it's simply translating multiple ORFs in succession. The closed loop model is interesting, but the authors say directly in the abstract that it's a part of polysome processing, which is the section you should have focused on. Additionally, as David said, this question should not have been answered. From How do I write a good answer? in the help center,
Answer well-asked questions. Not all questions can or should be answered here.$\endgroup$– MattDMoDec 31, 2016 at 1:37 -
1$\begingroup$ Since you are new here, I strongly suggest you take the tour and carefully read through the entire help center to learn more about the site, including what is on-topic and what is not. $\endgroup$– MattDMoDec 31, 2016 at 1:39