You allow one bacteria (circular DNA) to replicate in radioactive nucleotides so that any newly synthesized DNA strands use radioactive nucleotides. After 3 rounds of replication, how many DNA molecules have one strand of radioactivity and one strand without radioactivity?
To determine the number of DNA molecules that have one strand of radioactivity and one strand without radioactivity after 3 rounds of replication, we need to understand the process of DNA replication.
During replication, the double-stranded DNA molecule unwinds and each strand serves as a template for the synthesis of a new complementary strand. The newly synthesized DNA molecule consists of one parental strand and one newly synthesized strand.
Given that initially only one bacterium with circular DNA is allowed to replicate in radioactive nucleotides, after the first round of replication, there will be two DNA molecules, both of which will have one radioactive strand (from the radioactive nucleotides) and one non-radioactive strand (from the original DNA).
After the second round of replication, each of the two DNA molecules will give rise to two more DNA molecules. As a result, we will have a total of four DNA molecules. Two of these DNA molecules will have one radioactive strand and one non-radioactive strand, while the other two will have both strands non-radioactive.
Finally, after the third round of replication, each of the four DNA molecules will give rise to two more DNA molecules, leading to a total of eight DNA molecules. Out of these eight DNA molecules, four will have one radioactive strand and one non-radioactive strand, while the other four will have both strands non-radioactive.
Therefore, after three rounds of replication, there will be four DNA molecules that have one strand of radioactivity and one strand without radioactivity.