Question

Why does DNA sequencing reaction use one primer and PCR use two primers?

Answer 1

This is because in DNA Sequencing, we just have to find out the sequence of the DNA molecule and we can do it by using only one strand of DNA. If we will add one primer only, then it will amplify only one of the strands of DNA. One strand of DNA is enough to determine the sequence of the given DNA fragment.

But in case of PCR, we need to increase the copy number of the DNA fragment which we are having. If we will add only one primer, then the increase in the the copy number of the DNA fragment will be linear. One strand of the DNA will be only amplified and after every round of PCR cycle, we will get one more strand of DNA fragment. This will not be helpful because after 30 rounds of PCR cycle, we will get only 30 molecules of DNA which is not enough to perform an experiment. Therefore we need to add two primers which will lead to an exponential amplification of the DNA fragment. So after 30 years of PCR, using two primers, we will have billions of copies of the DNA molecule.

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