DNA transcription and replication

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simpleton
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DNA transcription and replication

Post by simpleton » Thu Mar 18, 2010 3:54 am

Dear all,

I'm quite confused with the DNA transcription now. Much as I understand, the RNA polymerase can only work in 5' -> 3' direction hence does it mean that it can only transcribe the template strand that is in 3' -> 5'? So what about the coding strand (the one in 5' ->3')? Can I say that the coding strand is there just to stabilise the whole DNA strucutre?

So the nucleotide sequences on the coding strand of the DNA (5' -> 3') does not consist of genes? :?:


Many thanks in advance!

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JackBean
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Post by JackBean » Thu Mar 18, 2010 7:02 am

well, that depends from which way you look to it. Imagine, that you have string of DNA from left to right, OK? Let's say it is:
5'-ACGTACGATACGATACGGCATG-3'
3'-TGCATGCTATGCTATGCCGTAC-5'

that is the same as:
3'-TGCATGCTATGCTATGCCGTAC-5'
5'-ACGTACGATACGATACGGCATG-3'
(I just changed the two strands), so, now you could imagine, that you will read the top strand (again), but from left to rigth, right? That would be in 5' -> 3' direction ;) And even, there is a START codon:
3'-TGCATGCTATGCTATGCCgtaC-5'


the DNA helix is completely symmetrical. If you have seen just the helix, you couldn't know, which strand is "coding" and which is "anti-sense". And definitely yes, both strand are coding (BTW this is in all basic MolBio books;)
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

simpleton
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Re: DNA transcription and replication

Post by simpleton » Thu Mar 18, 2010 10:25 am

hmm. So it means that depending on how the RNA polymerase reads the DNA duplex? And that both strands actually can be the template strand for transcription?

E.g.

3' ATGTAGTGTGTCAT 5' --> Gene 1
5' TACATCACACAGTA 3' --> Gene 2

Start codon highlight in bold.

Depending on the promoter sequence and the regulation of the expression of the specific genes; both gene 1 and 2 can be transcribed under different conditions? Am I right to say that?

Thanks in advance :)

simpleton
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Post by simpleton » Thu Mar 18, 2010 10:29 am

actually i had read quite a few books on genetics. but they didn't tell me if both strands are coding. they only mentioned the specific orientations required for RNA pol to work. or do you've a book to recommend? i read principles of genetics and essential of genetics.

thanks a lot :)

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JackBean
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Post by JackBean » Fri Mar 19, 2010 7:11 am

I think, that your directions are wrong, aren't they?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

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Post by simpleton » Fri Mar 19, 2010 1:21 pm

hmm.. ya should be

3' TACTAGTGTGTCAT 5' --> Gene 1 (DNA)
5' AUGCAUCUCUCUGUA 3' --> mRNA

so what i just said is it right? meaning both strand can actually carry a gene?

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Post by simpleton » Fri Mar 19, 2010 2:07 pm

yeah. managed to get the answer from a website! :D but still many thanks to jackbean!

for those interested, http://dwb4.unl.edu/Chem/CHEM869N/CHEM8 ... re4-3.html

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JackBean
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Post by JackBean » Sat Mar 20, 2010 8:07 am

definitely both strands carry genes
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

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Re:

Post by sunghoo » Sat Mar 20, 2010 6:48 pm

JackBean wrote:I think, that your directions are wrong, aren't they?

RNA polymerase adds nucleotides to the 3' end of a growing chain, I think the direction is wrong as well

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Post by simpleton » Fri Mar 26, 2010 9:08 am

Sunghoo, I still didn't get the direction right?

3' TACTAGTGTGTCAT 5' --> Gene 1 (DNA)
5' AUGCAUCUCUCUGUA 3' --> mRNA

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JackBean
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Post by JackBean » Fri Mar 26, 2010 9:24 am

it should be
5' ATGTAGTGTGTCAT 3' --> strand 1
3' TACATCACACAGTA 5' --> strand 2

and
3' TACTAGTGTGTCAT 5' --> strand 2 (DNA)
5' AUGCAUCUCUCUGUA 3' --> mRNA
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

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