A lab is working on drugs that disrupt cell division (a typical strategy for chemotherapy) and have developed drugs that inhibit DNA replication in tumor cells. You, being a curious grad student want to test each drug and figure out which DNA replication enzyme it targets. You grow bacteria in labeled medium, so as to label the existing DNA. Then you rinse off the label and expose bacterial cells to each of the new drugs – any new DNA will not have the label. Then you analyze the bacterial for problems with their DNA. For each set of data, form a hypothesis as to which of the enzymes involved in DNA replication is affected, and why it would lead to these results. Drugs may not completely inhibit ALL functions of any given enzyme.

When bacteria are exposed to drug A, we find mismatched base pairs in the newly synthesized DNA.

When bacteria are exposed to drug B, we find no evidence of any newly synthesized RNA or DNA. In fact, electron microscopy shows no evidence of replication forks forming at all.

When bacteria are exposed to drug C, we find newly synthesized DNA has occasional uracils (RNA) thrown into the mix.

When bacteria are exposed to drug D, we find newly synthesized DNA, but it is still in chunks, not one long strand.

When bacteria are exposed to drug E, we find that both strands of the original DNA are partially unwound, but replication has stalled due to kinks and knots in the sugar-phosphate backbone.