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DNA replication / Transcription wording

Hi All,

I received such a good response to my previous question, I’m trying my luck again 😊


DNA replication / Transcription

In my revision book, it states that DNA helicase breaks the hydrogen bonds, and then DNA polymerase joins the nucleotides together.

However, in the transcription section, they write as if RNA polymerase does a whole lot more. As in, breaks the hydrogen bonds, lines up the free nucleotides, joins them together and then separates the mRNA strand.

Does RNA polymerase just have a better work ethic and do more, or does it in fact do roughly the same as DNA polymerase, and it is just the wording that is poor?

One particular line from the book reads 'RNA Polymerase lines up the free nucleotides'. Surely it is a complementary base pairing that does this?

Is there such a thing as RNA helicase?
In transcription, DNA helicase breaks the hydrogen bonds and one strand acts as a template strand.
The free RNA nucleotides are attracted to the exposed bases and attach via complementary base pairing (AT,GC rule)
RNA polymerase joins the nucleotides together. - this is all RNA polymerase does !!

[ This a 6 mark response to a question on the process of transcription. (AQA) ]

I believe RNA helicase does exist, however, at AS Level we are not required to know about its presence/function we should just know that the strand separates itself away to form pre-mRNA (before splicing - the removal on introns) and DNA polymerase reforms the template strand with the other original DNA strand !!

Hope this is clear :smile:
Reply 2
Original post by moonbeige
In transcription, DNA helicase breaks the hydrogen bonds and one strand acts as a template strand.
The free RNA nucleotides are attracted to the exposed bases and attach via complementary base pairing (AT,GC rule)
RNA polymerase joins the nucleotides together. - this is all RNA polymerase does !!

[ This a 6 mark response to a question on the process of transcription. (AQA) ]

I believe RNA helicase does exist, however, at AS Level we are not required to know about its presence/function we should just know that the strand separates itself away to form pre-mRNA (before splicing - the removal on introns) and DNA polymerase reforms the template strand with the other original DNA strand !!

Hope this is clear :smile:

Thank you, much appreciated.
Original post by moonbeige
In transcription, DNA helicase breaks the hydrogen bonds and one strand acts as a template strand.
The free RNA nucleotides are attracted to the exposed bases and attach via complementary base pairing (AT,GC rule)
RNA polymerase joins the nucleotides together. - this is all RNA polymerase does !!

[ This a 6 mark response to a question on the process of transcription. (AQA) ]

I believe RNA helicase does exist, however, at AS Level we are not required to know about its presence/function we should just know that the strand separates itself away to form pre-mRNA (before splicing - the removal on introns) and DNA polymerase reforms the template strand with the other original DNA strand !!

Hope this is clear :smile:

Sorry but this is not correct.
No DNA helicase is involved in transcription, only in DNA replication.
Transcription and DNA replication are two fundamentally different processes. DNA replication requires unwinding the whole genome and synthesising it again! Transcription involves creating RNA from one strand of DNA in a single gene.

In DNA replication, DNA helicases unwind the DNA to create the replication bubble (region of separated DNA). Multiple DNA polymerases bind to primer-DNA regions in replication bubble to synthesise new DNA in both directions.


In transcription, RNA polymerase alone cannot initially separate the DNA strands but requires the binding of transcription factors to separate the strands (NOT DNA helicase).
Once RNA polymerase starts moving along the DNA (note: double stranded DNA), the DNA strands separate within the enzyme (due to a structure in the enzyme called the "rudder" ) and leave the enzyme double stranded again. There is a region within RNA polymerase where the two DNA strands are separate and the RNA strand is peeled off the DNA and leaves the enyzme.
1844-1.gif

Original post by jonny1985_2
x
(edited 2 years ago)
Reply 4
Original post by Felynalanine
Sorry but this is not correct.
No DNA helicase is involved in transcription, only in DNA replication.
Transcription and DNA replication are two fundamentally different processes. DNA replication requires unwinding the whole genome and synthesising it again! Transcription involves creating RNA from one strand of DNA in a single gene.

In DNA replication, DNA helicases unwind the DNA to create the replication bubble (region of separated DNA). Multiple DNA polymerases bind to primer-DNA regions in replication bubble to synthesise new DNA in both directions.


In transcription, RNA polymerase alone cannot initially separate the DNA strands but requires the binding of transcription factors to separate the strands (NOT DNA helicase).
Once RNA polymerase starts moving along the DNA (note: double stranded DNA), the DNA strands separate within the enzyme (due to a structure in the enzyme called the "rudder" ) and leave the enzyme double stranded again. There is a region within RNA polymerase where the two DNA strands are separate and the RNA strand is peeled off the DNA and leaves the enyzme.
1844-1.gif

Many thanks for the further information.

The simplification of complex processes in my study books (AS Level) creates so many additional questions. The answers however are beyond my level of comprehension…at the moment. Fascinating nevertheless!
Reply 5
Original post by Felynalanine
Sorry but this is not correct.
No DNA helicase is involved in transcription, only in DNA replication.
Transcription and DNA replication are two fundamentally different processes. DNA replication requires unwinding the whole genome and synthesising it again! Transcription involves creating RNA from one strand of DNA in a single gene.

In DNA replication, DNA helicases unwind the DNA to create the replication bubble (region of separated DNA). Multiple DNA polymerases bind to primer-DNA regions in replication bubble to synthesise new DNA in both directions.


In transcription, RNA polymerase alone cannot initially separate the DNA strands but requires the binding of transcription factors to separate the strands (NOT DNA helicase).
Once RNA polymerase starts moving along the DNA (note: double stranded DNA), the DNA strands separate within the enzyme (due to a structure in the enzyme called the "rudder" ) and leave the enzyme double stranded again. There is a region within RNA polymerase where the two DNA strands are separate and the RNA strand is peeled off the DNA and leaves the enyzme.
1844-1.gif

Agreed, there is no DNA helicase in transcription, RNA polymerase and general transcription factors have helicase activity.
Original post by jonny1985_2
Hi All,
I received such a good response to my previous question, I’m trying my luck again 😊
DNA replication / Transcription
In my revision book, it states that DNA helicase breaks the hydrogen bonds, and then DNA polymerase joins the nucleotides together.
However, in the transcription section, they write as if RNA polymerase does a whole lot more. As in, breaks the hydrogen bonds, lines up the free nucleotides, joins them together and then separates the mRNA strand.
Does RNA polymerase just have a better work ethic and do more, or does it in fact do roughly the same as DNA polymerase, and it is just the wording that is poor?
One particular line from the book reads 'RNA Polymerase lines up the free nucleotides'. Surely it is a complementary base pairing that does this?
Is there such a thing as RNA helicase?

Haha I have the same CGP revision guide and had the same question as you. At least now we know what transcription factors are so we can understand how it works!
(edited 1 month ago)

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