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AS Biology - PCR & Electrophoresis watch

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    Hello, I was wondering if anyone could help me . . .

    1) I can't get my head around what the primers are for in PCR

    2) What exactly does the radioactive probe do in electrophersis? And what's with the photographic film?!

    I'd be really grateful if someone could explain these things to me!

    I'm doing the AQA B spec.

    Thank you!
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    (Original post by ButterCookie)
    Hello, I was wondering if anyone could help me . . .

    1) I can't get my head around what the primers are for in PCR

    2) What exactly does the radioactive probe do in electrophersis? And what's with the photographic film?!

    I'd be really grateful if someone could explain these things to me!

    I'm doing the AQA B spec.

    Thank you!
    Primers are short sequences of DNA used to 'prime' the construction of a larger peice of DNA. Think of it a bit like a base coat of paint - required to allow your top layer of paint to stay put. Another way is to think of a string of beade. The primer is the first 5 beads. You then add to it to make a neck lace.


    Radioactive probes allow you to detect specific sequences of DNA on a gel. Usually a radioactive probe is a short sequence of DNA complementary to the sequence you are looking for. It's made radioactive usually by addition of P32.

    You usually blot your gel and then add your probe to hybridise.
    Radio activity can be picked up on photographic film - it gives a dark patch ont he plate. It will light up and tell you which bands from your gel contain the sequence of DNA you are looking for.

    Edited to add: PS the above gel/blot technique is called Southern blotting.
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    Southern blotting:

    http://www.biology.washington.edu/fingerprint/blot.html

    The picture with the black bands is representing an ethidium stained gel. The piccy with the red bands is depicting the photographic film (showining where the p32 signals are)
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    Just to add to that..

    1) The primers are needed because DNA polymerase can't work without a starting base pair (err, that's not the best way to put it really tho - jus can't fink straight right now).. I like to picture a zip. The DNA polymerase needs the zip to have been.. started! Lol.. make sense?

    2) See Fluffy's post.
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    Thank you both for your help!
 
 
 

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