Question

Bacterial cells have only one DNA molecule, which is double-stranded and is replicated in essentially the same fashion as in eukaryotes. Imagine that, following the techniques of other scientists studying DNA, you created a bacterial cell that contains only radioactive nitrogen in its DNA. You then place the cell in a culture medium containing only ""regular"" (nonradioactive) nitrogen. Based on this scenario and your knowledge of DNA structure and replication, how many cells will contain some DNA with radioactive nitrogen after four rounds of cell replication?

a) 2
b) 4
c) 8
d) 16

Answer 1

After four rounds of cell replication in a bacterial cell originally containing radioactive nitrogen in its DNA, eight cells will contain some DNA with radioactive nitrogen.

Step-by-step explanation:

The question is based on the principles of DNA replication, specifically the semiconservative nature of the process. In semiconservative DNA replication, each new DNA molecule consists of one old (parental) and one new (daughter) strand. Given a bacterial cell that has incorporated radioactive nitrogen into its DNA, after one round of replication, there would be two cells, each with one strand of DNA containing radioactive nitrogen. After the second round, there would be four cells, two of which contain DNA with one radioactive strand. Following this pattern, after the third round, there would be eight cells, four with one radioactive strand of DNA. Finally, after the fourth round of replication, there would be sixteen cells, but only eight of those would contain DNA with radioactive nitrogen.

Therefore, the correct answer to how many cells will contain some DNA with radioactive nitrogen after four rounds of cell replication is: c) 8