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PCR A level biology

Could someone please explain this aspect of PCR: so there are two primers, each bind to each end of the target gene on the opposite strands of DNA. DNA polymerase then adds nucleotides to each end to amplify the dna region between them. But how does it know when to stop? Does it just amplify all the DNA after the gene? Thanks.
Reply 1
In PCR you're working with fragments of DNA that have been cut by restriction enzymes, so DNA polymerase just amplifies each individual fragment.

Hope this helps :smile:
Reply 2
Original post by cyberhex
In PCR you're working with fragments of DNA that have been cut by restriction enzymes, so DNA polymerase just amplifies each individual fragment.

Hope this helps :smile:

Ohhh ok. So would some of the DNA fragment be amplified that doesn’t contain the gene?
Reply 3
Original post by Har6547
Ohhh ok. So would some of the DNA fragment be amplified that doesn’t contain the gene?

Yeah so the whole fragment would be amplified so if the fragment contains introns or something as well as the gene then this will be replicated too.
Reply 4
Original post by cyberhex
Yeah so the whole fragment would be amplified so if the fragment contains introns or something as well as the gene then this will be replicated too.


How would that work for genetic fingerprinting though? Once the DNA has been cut into fragments, is PCR used to make copies of all the fragments? How would this compare VNTRs though?
Reply 5
Original post by Har6547
How would that work for genetic fingerprinting though? Once the DNA has been cut into fragments, is PCR used to make copies of all the fragments? How would this compare VNTRs though?

Yeah, I think it copies all the fragments. I'm afraid I'm not sure about VNTRs, it's been a long time since I looked over them lol

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