Which direction is mRNA synthesised?

[ennui]

DNA is read 5' to 3'. But when the mRNA is being synthesized by the RNA polymerase- is the mRNA created 3' first or 5' first?

 

e.g.

 

Imagine that below is the double-stranded DNA. The gene needed to be transcribed is in bold.

 

5'-AGTGGGCCG-3'

3'-TCACCCGGC-5'

 

So the DNA is now unwound by a helicase, and all the transcription factors are bound, etc. Below is the template DNA strand (with the gene required) in black, and the new mRNA in red.

 

But which way does it go?

 

5'-AGTGGGCCG-3'

5'-UCACC>>>>

 

I'd imagine something like this. But can the mRNA (red) align with the template DNA both in the same direction?

 

Can anyone help me understand the directions of RNA synthesis? I'm a little confused about it.

[MedGen]

DNA is read 5' to 3'. But when the mRNA is being synthesized by the RNA polymerase- is the mRNA created 3' first or 5' first?

 

e.g.

 

Imagine that below is the double-stranded DNA. The gene needed to be transcribed is in bold.

 

5'-AGTGGGCCG-3'

3'-TCACCCGGC-5'

 

So the DNA is now unwound by a helicase, and all the transcription factors are bound, etc. Below is the template DNA strand (with the gene required) in black, and the new mRNA in red.

 

But which way does it go?

 

5'-AGTGGGCCG-3'

5'-UCACC>>>>

 

I'd imagine something like this. But can the mRNA (red) align with the template DNA both in the same direction?

 

Can anyone help me understand the directions of RNA synthesis? I'm a little confused about it.

 

Synthesis is always in the 5' to 3' direction. The key to is to remember that the strands are anti-parallel. The actual direction of transcription whether on the + or - strand depends on the position of the promoter elements.

The strand that will contain the same sequence as the mRNA is known as the sense strand, and the one that is actively transcribed from is the anti-sense strand.

 

Here's a little representation using your example:

5'-AGTGGGCCG-3' - sense strand +

3'-TCACCCGGC-5' - anti-sense strand -

 

3'-TCACCCGGC-5' - anti-sense strand

5'-AGUGGGCCG>>>>>>3' - mRNA

 

If the gene was transcribed in the opposite orientation:

5'-AGTGGGCCG-3'[/b] - anti-sense strand +

3'-TCACCCGGC-5' - sense strand -

 

5'-AGTGGGCCG-3'

3'<<<<<UCACCCGGC-5' - mRNA

 

 

Note that the denotion of + or - remains the same. So the orientation of the gene itself is denoted by whether it appears on the + strand or - strand. This is for the purpose of having a constant reference when mapping genes to a specific locus and aligning sequences, particularly with respect to transcriptional direction and retrotransposed elements, but that's another story.

Hope that helps answer your question.

[ennui]

That's pretty helpful, thanks. I googled a couple of diagrams, too.

 

I have a terrible time with orientations and the double-strandedness of genetics. Holliday junctions are a nightmare for me to wrap my head around, too.

[ecoli]

it's all pretty confusing, because its based around spatial orientation we can't possibly observe. Good luck tho.