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 ʺregularʺ (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) 4
B) 8
C) 1
D) 2
E) 16

Question

Quizplus · Accepted Answer

After the first round of replication, the original DNA molecule with radioactive nitrogen will have produced two new molecules, each consisting of one original (radioactive) strand and one new (nonradioactive) strand. In subsequent rounds of replication, only one of these molecules will continue to divide, halving the number of cells with radioactive DNA in each round. After four rounds, there will be one cell with a completely radioactive strand and one cell with a strand that is half radioactive, totaling two cells containing some DNA with radioactive nitrogen.

Bacterial Cells Have Only One DNA Molecule, Which Is Double