DNA replication

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NewtoBiology
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DNA replication

Post by NewtoBiology » Sun Jun 29, 2008 1:54 am

Hello,

I am a new biology student, and I am wondering if someone can double check my listed order of DNA replication, which I have created to make sure I am chronologically correct, prior to me memorizing all the steps

1. Helicase begins unwinding DNA
2. Primase catalyzes the formation of an RNA primer
3. DNA polymerase begins replication by adding nucleotides to the 3’ end of the primer
4. Okazaki fragments are formed
5. Okazaki fragments are ligated together to form a single continuous DNA strand.


Just having an issue with 2 and 3. Could nucleotides at the 3' end of the primer be laid prior to RNA primer???

THANK YOU!!!

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MrMistery
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Post by MrMistery » Sun Jun 29, 2008 9:54 am

Your list is correct, but only for the lagging strand. For the leading strand, things are simpler: no Okazaki fragments are required and the elongation of the new DNA strand is continuous.

Certainly nucleotides could not be added to the 3' of the primer before the primer is in place - in fact that is why the primer exists. DNA polymerases cannot synthesize a DNA strand de nuovo, they need a free 3'-OH on which to add nucleotides. That is where primase comes in: like all RNA polymerases, primase can initiate the synthesis of an RNA strand de nuovo, providing a free 3'-OH on which DNA polymerase III(or the eukaryotic equivalent ) can act. Also, you might consider adding another stage between 4 and 5: the RNA primer is substituted for DNA by the enzyme DNA polymerase I(or the eukaryotic equivalent).

Cheers,
Andrew
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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Post by NewtoBiology » Sun Jun 29, 2008 1:04 pm

Thank you very much Mr.Mistery.

I will definitely add that between 4 and 5 to make my lagging strand description complete.

Thank you for your time and explanation!!

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