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While going over PCR in my biology lecture this week I have come across a few questions I have about this process.

First, since PCR focuses on trying to replicate a specific targeted DNA sequence many times in a short amount of time, are the primers used in every cycle the same sequence? I understand the forward and reverse primers would not be the same but the forward primer for one strand in one cycle, would it be the same as the forward primer for a daughter strand of let's say the 8th cycle?

Second, why are primers not reusable for different cycles? I think this would be based off of the answer to my first question. If the primers are essentially the same sequence, why do new primers have to be used for every cycle?

Thank you in advance!

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are the primers used in every cycle the same sequence?

Yes. You put the whole reaction on the thermocycler, and then walk away until all the cycles are complete.

But one could do a second round of PCR with different internal primers on that first PCR product, if you wanted.

Second, why are primers not reusable for different cycles?

Are you asking why you can't put in 10 molecules of forward primer and get a million product molecules from that?

Each molecule of primer that is used as an extension template is incorporated into a whole stand of PCR product. It's not a primer any more.

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The primer is incorporated into the start of the new strand. The number of dna strands produced is limited by the number of primers.

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