Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 129

1 1. Some viruses, such as adenovirus, avoid the problem of lagging-strand synthesis by replicating the individual strands of the DNA in the leading-strand direction simultaneously from both ends so that eventually the entire molecule is replicated. Why do bacterial chromosomes not replicate in this way?

2 2. Why are DNA molecules so long? Would it not be easier to have many shorter pieces of DNA? What are the advantages and disadvantages of a single long DNA molecule?

3 3. Why do cells have DNA as their hereditary material instead of RNA, like some viruses?

4 4. What effect would shifting a temperature-sensitive mutant with a mutation in the dnaA gene for initiator protein DnaA have on the rate of DNA synthesis? Would the rate drop linearly or exponentially? Would the slope of the curve be affected by the growth rate of the cells at the time of the shift? Explain.

5 5. The gyrase inhibitor novobiocin inhibits the growth of almost all types of bacteria. What would you predict about the gyrase of the bacterium Streptomyces sphaeroides, which makes this antibiotic? How would you test your hypothesis?

6 6. How do you think chromosome replication and cell division are coordinated in bacteria like E. coli? How would you go about testing your hypothesis?

7 7. Why is termination of chromosome replication so sloppy that the ter region is nonessential for growth and there has to be more than one ter site in each direction to completely stop the replication fork? What are the advantages of not having a definite site on the chromosome at which replication always terminates?