dr.shar
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If c-DNA is made from m-rna, is untranlated region of m-rna trancribed by Reverse transcriptase.....
in another words if m-RNA has 100 Bp in untranslated region and 300 Bp in coding region, how many base pairs will be present in C-DNA by reverse trancriptase....
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| rida
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I would say 300 Bp because only the coded ones get transcribed with reverse transcriptase, not the untranslated one....could be wrong tho....
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| Idiopathic
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Reverse transcriptase is used for cloning mature mRNA, therefore, the introns would be cut out first. 300bp would be coded, if that is the translated region.
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| dr.shar
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i am still in doubt, i has done a clinical vignette in kaplan, ths answer is given as 400bp... can you explain anyone....
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| asmi
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i think its just that we have to add it up..100+300 ( sine its asking how many basepairs in C-DNA...
:roll: i hope iam right !! If not then plz explain ..
Thanks
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| jalabert
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Introns are different than untranslated regions (UTRs). Think about what the name says, Un Translated, not untranscribed. So, introns would not be present, but the UTR would be. The mRNA has already had the introns excised, the cDNA would simply reverse transcibe what is present in the mRNA, including the UTR. So, the answer would be 400.
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| bims
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i think i agree with what jalabert said but i could be wrong.
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| dr.shar
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please let me know how untranslated region will be trancribed by Reverse transcriptase in order to produce one C DNA molecule
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| faiza
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i am in doubt that a mrna has any un translated region b/c introns are left inside the nucleus and exons come in cytoplasm :?:
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| jalabert
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My molecular biology is a bit rusty, but for generating cDNA, this is a pretty central concept. To generate a specific cDNA by reverse transcription (RT), you isolate the mRNA for the specific gene. The mRNA has the expressed portion of the transcript and a poly A tail that specifies that the mRNA will be transported from the nucleus to the cytoplasm for translation. When you isolate the mRNA, it has the untranslated poly A tail. When doing the RT-PCR, you can use oligoT primers that recognize the poly A tail and will begin the reverse transcription there. So, if you do this, you will end up with the transcibed anti-strand of DNA, complementary to the initial mRNA strand, and this will contain the poly/oligo T, unexpressed region. The mRNA strand is then degraded with alkali, and the sense strand of DNA is replicated from the anti-strand. End result, double stranded cDNA with expressed region, no introns, but the additional oligoT/A sequence that began as the poly A tail from the mRNA. Therefore, from the original question, 300 bp + 100 bp untranslated, although that's a rather large UTR. Some retroviruses use the same principle (e.g. HIV) and I believe their UTRs are longer than the traditional UTR that would be simply derived from the poly A tail, but that's another question.
Hope this clears it up.
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| dr.shar
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jalabert
thankyou very much, you are appriciated///
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