Question: Could you please explain PCR, I missed the chance in chat?

Wei Xun answered on 15 Jun 2011:

hi 05braceye!

PCR stands for polymerase chain reaction, it’s a process you can make lots and lots of copies of a section of DNA exactly.

So let’s start by looking at DNA. It’s a double helix of two sugar-chains which have four molecules called nucleotides attached that stick out in the same direction, rather like the teeth on a zip. Normally, the two strands of DNA are “zipped” together and wound very tightly so they can fit into the nuclei of cells.

1st step of PCR would be to straighten the double DNA strand and then it is unzipped, so you get two strands with complementary nucleotide sequences, we can achieve this by heating.

Then “primers” are added, they look for and lock onto the codes on the DNA strands which tell you that the gene you want to copy starts there. An enzyme is then added called polymerase, which locks onto that start signal and gets ready to start copying. After which we add a mixture of the four nucleotides need to make DNA and the polymerase “stitches” them all in the right sequence into another strand of DNA. So now instead of one double-strand DNA, you have two double strands.

If we repeat the process from the start, 2 copies become 4, 4 become 8 etc, so in 6 cycles, we have 32 copies of 1 double strand. You can see how quickly we will get to large numbers of copies.

I found a video on youtube that explains this very well: http://is.gd/dSaCQm