Question

A PCR was setup to amplify a 500 nucleotides-long DNA. The dNTPs in the reaction mixture were radiolabeled. The percentage (%) of radiolabeled single-stranded DNA after three cycles will be ............ (up to one decimal place)

Hint:

In PCR, the percentage of radiolabeled DNA increases after each cycle as new strands are synthesized, with each new cycle incorporating radiolabeled dNTPs.

Answer 1

Correct Answer: 87.5

In a PCR reaction, each cycle results in the doubling of the DNA, and in each cycle, the newly synthesized DNA strands incorporate radiolabeled dNTPs. For the first cycle, half of the newly synthesized DNA will be radiolabeled. After each subsequent cycle, half of the newly synthesized DNA in each cycle will be radiolabeled.
- After cycle 1, half of the new DNA strands will be radiolabeled, meaning 50% of the total DNA is radiolabeled.
- After cycle 2, half of the newly synthesized DNA will be radiolabeled again, which means 75% of the DNA will be radiolabeled.
- After cycle 3, half of the newly synthesized DNA will again be radiolabeled, bringing the total percentage of radiolabeled DNA to 87.5%.
Thus, after three cycles, the percentage of radiolabeled single-stranded DNA will be 87.5%.