Cell and Molecular Biology: Concepts and Experiments

Gerald Karp

Chapter 13

DNA Replication and Repair - all with Video Answers

Educators

Chapter Questions

Problem 1

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?

Rabeya Zahid

Rabeya Zahid

Numerade Educator

Problem 2

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?

Rabeya Zahid

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Problem 3

How would the chromosomes from the experiment on eukaryotic cells depicted in Figure 13.4 have appeared if replication occurred by a conservative or a dispersive mechanism?

Rabeya Zahid

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Problem 4

We have seen that cells possess a special enzyme to remove uracil from DNA. What do you suppose would happen if the uracil groups were not removed? (You might consider the information presented in Figure 11.44 on the pairing properties of uracil.

Rabeya Zahid

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Problem 5

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

Rabeya Zahid

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Problem 6

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?

Rabeya Zahid

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Problem 7

Suppose the error rate during replication in human cells were the same as that of bacteria (about $10^{-9}$ ). How would this impact the two cells differently?

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Problem 8

Figure 13.19 shows the results from an experiment in which cells were incubated with $\left[^{3} \mathrm{H}\right]$ thymidine for less than $30 \mathrm{min}$ utes prior to fixation. How would you expect this photograph to appear after a one-hour labeling period? Can you conclude that the entire genome is replicated within an hour? If not, why not?

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Problem 9

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?

Bryan Valdivia

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Problem 10

What are the advantages of replication occurring in a small number of replication foci rather than in the general nucleoplasm?

Kyle Ukes

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Problem 11

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

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Problem 12

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?

Rabeya Zahid

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Problem 13

Construct a model that would explain how transcriptionally active DNA is repaired preferentially over transcriptionally silent DNA.

Rabeya Zahid

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