Chapter 13

Suppose that Meselson and Stahl had carried out their experiment by growing cells in medium with \(^{14} \mathrm{N}\) and then transferring the cells to medium containing \(^{15} \mathrm{N}\). How would the bands within the centrifuge tubes have appeared if replication were semiconservative? If replication were conservative? If replication were dispersive?

Suppose you isolated a mutant strain of yeast that replicated its DNA more than once per cell cycle. In other words, each gene in the genome was replicated several times between successive cell divisions. How might you explain such a phenomenon?

Draw a partially double-stranded DNA molecule that would not serve as a template for DNA synthesis by DNA polymerase I.

Some temperature-sensitive bacterial mutants stop replication immediately following elevation of temperature, whereas others continue to replicate their DNA for a period of time before they cease this activity, and still others continue until a round of replication is completed. How might these three types of mutants differ?

Origins of replication tend to have a region that is very rich in A-T base pairs. What function do you suppose these sections might serve?

What are some of the reasons you might expect human cells to have more efficient repair systems than those of a frog?

Suppose you were to compare autoradiographs of two cells that had been exposed to \(\left[^{3} \mathrm{H}\right]\) thymidine, one that was engaged in DNA replication (S phase) and another that was not. How would you expect autoradiographs of these cells to differ?