TPR Bio Diagnostic (DNA Replication)

[Synapsis]

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Spoiler below, if you plan on taking this diagnostic at some point.

130. Which of the following initially binds to single-stranded DNA during replication?
A. Helicase
B. RNA Polymerase
C. DNA Polymerase III
D. DNA Ligase

Answer: B

...Did I completely miss something in my content review? Helicase and Ligase are immediately out because helicase doesn't directly bind DNA and DNA Ligase links only dsDNA, and cannot bind ssDNA. Since this is DNA replication, why will DNA Pol III not bind ssDNA? Why would RNA Pol even be involved?

 

[MJS4878]

Is there an explanation to the anser? As stated, this can't be right ...

 

[FeinMS]

RNA polymerase must bind first to produce RNA primer. DNA polymerase can't initiate the repolication de novo. It needs a template with a free 3' OH to elongate newly synthesized DNA and the template is what we call RNA primer.

 

[MJS4878]

RNA polymerase must bind first to produce RNA primer. DNA polymerase can't initiate the repolication de novo. It needs a template with a free 3' OH to elongate newly synthesized DNA and the template is what we call RNA primer.

Dammit... why didn't I think of that

 

[Synapsis]

RNA polymerase must bind first to produce RNA primer. DNA polymerase can't initiate the repolication de novo. It needs a template with a free 3' OH to elongate newly synthesized DNA and the template is what we call RNA primer.

Right. I guess the reason I missed that was because I'm so used to seeing "Primase" or "RNA Primase" that I basically forgot that Primase is an RNA Polymerase. Thanks a lot for the reminder. Amazing how you can test the same basic thing in a million ways just by changing wording. This is a fantastic question.

 

[enervate]

...Did I completely miss something in my content review? Helicase and Ligase are immediately out because helicase doesn't directly bind DNA and DNA Ligase links only dsDNA, and cannot bind ssDNA. Since this is DNA replication, why will DNA Pol III not bind ssDNA? Why would RNA Pol even be involved?

Helicase doesn't bind to DNA?

 

[Synapsis]

Helicase doesn't bind to DNA?

To my knowledge, it was part of the replisome, but it didn't directly bind ssDNA. Quick google search proved that wrong.

http://www.evolutionnews.org/2013/02/unwinding_the_d_1069371.html

 

[enervate]

To my knowledge, it was part of the replisome, but it didn't directly bind ssDNA. Quick google search proved that wrong.

http://www.evolutionnews.org/2013/02/unwinding_the_d_1069371.html

Yeah, but the scope is irrelevant. Everything in that article that refers to helicase binding ssDNA indicates that it does so in the process of dsDNA replication. Your question seems to refer to binding "loose" ssDNA. For example, you've got an isolated strand of ssDNA in vivo. Of course helicase shouldn't bind that strand; it's already unwound.

Let me rephrase my original question: isn't helicase the first to bind dsDNA during replication?

PS: why aren't you on AIM anymore?