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DNA Probes

Hi guys, could somebody explain how DNA Probes actually bind to their complementary strand or fragmented DNA? All my text books say they bind to their strand via base pairing but - as the image attached shows - isn't the strand already double stranded?

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In what context are you doing this? The only reason that this will happen is if the DNA has already "unzipped" to become single stranded. In PCR, for example, this happens through the increasing the temperature, while in cells during replication and transcription it's through the action of several enzymes and binding proteins.
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Avatar for Tillybop
Tillybop
18
Original post by MarkProbio
Hi guys, could somebody explain how DNA Probes actually bind to their complementary strand or fragmented DNA? All my text books say they bind to their strand via base pairing but - as the image attached shows - isn't the strand already double stranded?

Posted from TSR Mobile


From the image I guess you're talking about the primers that attach to the specific binding sites on the DNA during PCR. The strand is split apart before this. The first stage of PCR involves splitting the double strand by heating it. The primers are then added and it is cooled to allow them to join. They will join on to where the nucleotides are complementary. :smile:
Reply 3
Avatar for MarkProbio
MarkProbio
OP
7
Thanks for your replies. The specification says "Describe how DNA probes can be used to identify fragments containing specific sequences." So this is the context I am given. We haven't come to PCR yet (that's next).

This is a diagram from another book I have.

Going from this book, I also don't understand why the fluorescent probe shows the specific fragment is there. Surely you'd be able to see it whether it was bound to it or not?
(edited 10 years ago)
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Reply 4
Avatar for KanKan
KanKan
11
Original post by MarkProbio
Surely you'd be able to see it whether it was bound to it or not?


You forget just how small DNA actually is! We can't see a specific gene using a microscope, some genes are only 60 base pairs long.

Using a florescent marker that already complements the gene you are looking for (you can order these online - it's really cool), you can test if the sample contains that gene (as the sample will glow).
Reply 5
Avatar for MarkProbio
MarkProbio
OP
7
Original post by KanKan
You forget just how small DNA actually is! We can't see a specific gene using a microscope, some genes are only 60 base pairs long.

Using a florescent marker that already complements the gene you are looking for (you can order these online - it's really cool), you can test if the sample contains that gene (as the sample will glow).


I meant surely you'd be able to see it (under a decent microscope) regardless of whether the probe had annealed or not. But I guess you'd be able to see it bound to the longer gene. Cheers for the response. :smile:

I guess I will just assume the heat from the incubater breaks the hydrogen bonds so the probe can hybridise, although neither book makes that clear. So annoying!
(edited 10 years ago)

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