What do you do to "prepare" genomic DNA prior to using it in a Polymerase Chain Reaction?

Question

Hey,

I'm in a genetics class (without a lab), and I'm trying to understand PCR from a textbook. The steps of PCR itself seems straightforward enough (in theory, anyway), but it says that the first step is to "prepare a small amount of genomic DNA", and does not give any more detail than that.

What does it mean by "prepare" the genomic DNA? What are you supposed to do to it?

I do not have any understanding of what you are supposed to between the steps of extracting the DNA from an organism (say, by taking a blood sample) and then putting it in your vial with your primers and Taq DNA polymerase and everything else.

Surely you do not just add entire drops of blood to your vial, do you?

I do not need enough details to be able to perform the procedure, but a conceptual understanding would be very nice.

Thank you very much. :)

Answer 1

In order to perform PCR, you need a pure sample of nothing but DNA (or RNA if that's what you happen to be amplifying). So you need to get rid of everything else that starts out in your sample. So if your initial sample were a vial of blood, you would centrifuge it to separate the blood cells from the plasma, then you would have to break the cells apart and wash all the cell membranes, nutrients, and other "junk" out of your sample. When all you have left is DNA, you can then add your primers, polymerase, and A, G, C, T/U building blocks. Now you're ready for the actual chain reaction to take place.

Answer 2

Prepare would mean doing a DNA extraction on whatever cells you are getting it from.  This removes RNA, protein, lipids, ect from the sample.

Once you actually get the DNA you're done with that part.

Answer 3

depends... if you have purified genomic DNA already, you don't need to prepare it (other than to maybe dilute it if it's very concentrated).

otherwise, you will have to extract it from your cells or tissue or whatever  for pcr, you can use a whole cells directly (as long as it's not too much, but this is probably not what you want to do).