The polymerase chain reaction (PCR) is a technique used in molecular biology to make millions of copies DNA from a small amount of it. To acomplish this, short segments of DNA called primers are designed to each chain of the DNA that is going to be copied. Then, the DNA polymerase adds nucleotides to theose primers that will be complementary to the DNA chains. After one molecule is amplified, a new molecule is amplified using that one and so on and so forth. Then, 2 chains are amplified in one cycle to get 2 molecules (with two chains each) Thereby, the replication rate of DNA is exponential, then it is calculated as:
1 x (2^4) = 16 DNA molecules.
2= chains per molecule
4= number of cycles
The PCR technique is based on the amplification - in vitro - of a single DNA sequence millions of times. Basically it makes several copies of the fragment of interest of the DNA that will be studied.
PCR occurs in three steps and they all depend on a temperature gradient.1st step: Denaturation (at 95ºC) of the double strand of DNA, which occurs due to the rise in temperature. 2nd step: Priming (57ºC to 63ºC) of the primers, which can occur in a temperature variation between 57ºC to 63ºC. 3rd step: Extension (at 72ºC) with the operation of Taq Polymerase, which helps in the introduction of nucleotides that will complement the chain being synthesized.
The three steps together form one cycle, a normal PCR has around 36 cycles. As each DNa molecule will form 2 new molecules it is possible how many DNA molecules a single DNA molecule will form in each cycle. To do this, you must calculate "2^n", where "n" corresponds to the number of cycles.
So, to know how many DNA molecules would result from a molecule after four cycles of PCR, you have to calculate 2^4 = 16 molecules.
A.16 is the answer
It is because, it gets double at every stage2^4 = 16.
PCR, assuming sufficient primers, dNTP’s, and polymerase molecules, doubles the number of target DNA molecules per cycle. 5 cycles corresponds to 5 doublings of the target DNA. 2x2x2x2x2, or 2 to the 5th power is 32.
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