PCR quick question

[betterfuture]

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Okay. This may be a really stupid question and I may be thinking to hard but for PCR, if you have a broken or impure sample of a DNA, doesn't that mean that it is not the whole DNA? As in, it is only a SEGMENT of a DNA? So say if one performs a PCR and takes that broken/impure sample of DNA, then only that specific segment of DNA is copied, correct?

I was under the assumption that somehow PCR will make multiple copies of an organism's entire DNA, like every gene? Someone please help me if I am wrong somewhere in my statements. Thank you.

 

[aldol16]

Why do you do PCR? You do PCR to amplify a certain sequence of DNA. If you wanted to replicate an entire genome, it would be much more economical to just let the cell divide and take the DNA from the daughter cells.

 

[betterfuture]

How would you replicate an entire genome off a broken DNA sample?

 

[aldol16]

How would you replicate an entire genome off a broken DNA sample?

You can't. The point was that even if you could design a PCR that does not first digest the DNA, it would be more economical to let the cell replicate and then just use the daughter cell's whole genome.

 

[betterfuture]

Thanks!

 

[yeasureyoubetcha]

Okay. This may be a really stupid question and I may be thinking to hard but for PCR, if you have a broken or impure sample of a DNA, doesn't that mean that it is not the whole DNA? As in, it is only a SEGMENT of a DNA? So say if one performs a PCR and takes that broken/impure sample of DNA, then only that specific segment of DNA is copied, correct?

PCR will only amplify the sequence between the forward and reverse primers. If a DS break interrupts the amplicon then that sequence will not amplify. Usually DS breaks are random, and there will be enough template sequence for this not to matter so the reaction will still proceed.

I was under the assumption that somehow PCR will make multiple copies of an organism's entire DNA, like every gene? Someone please help me if I am wrong somewhere in my statements. Thank you.

To do that, at least for the human genome, you would need several hundred thousand primer sets. Its more economical as others may have mentioned just to culture cells and do a total DNA extraction.

 

[betterfuture]

PCR will only amplify the sequence between the forward and reverse primers. If a DS break interrupts the amplicon then that sequence will not amplify. Usually DS breaks are random, and there will be enough template sequence for this not to matter so the reaction will still proceed.


To do that, at least for the human genome, you would need several hundred thousand primer sets. Its more economical as others may have mentioned just to culture cells and do a total DNA extraction.

Thanks for clarifying. All these years I could never really fully understand till now. Makes perfect sense now.