Final answer:
In PCR, the number of DNA molecules doubles after each cycle. Starting with 5 pieces of initial DNA, 40 pieces would be present after 3 cycles. This exponential amplification process is central to the PCR technique.
Step-by-step explanation:
The Polymerase Chain Reaction (PCR) is a powerful technique used to amplify DNA sequences. Starting with 5 pieces of DNA, after 3 cycles of PCR, there would be 40 pieces of DNA. This is because the PCR process doubles the number of DNA sequences with each cycle. Thus, after n cycles the quantity of the desired DNA sequence becomes 2n. This substantial increase in DNA quantity through PCR is why it's also referred to as a chain reaction.
During the PCR cycle, temperatures are cycled between three stages: denaturation, annealing, and DNA synthesis. These stages respectively occur at high, low, and intermediate temperatures. The denaturation stage, typically at around 94°C, separates the double-stranded DNA. During annealing, at about 55°C, primers bind to each DNA strand. Finally, in the extension or synthesis stage, at around 72°C, the enzyme Taq polymerase synthesizes new DNA strands.
To illustrate this concept, after 3 cycles starting with a pair of complementary target DNA molecules, one would theoretically end up with 40 double-stranded PCR products. If this process were extended to 30 cycles, the number of DNA molecules would reach a massive amplification. Specifically, for a complete 30-cycle PCR, you would expect to have 230 times the original amount of DNA fragments, assuming ideal conditions and 100% efficiency in each cycle.