MCB 229 Spring 2000 Study Guide 15 Prof. Terry

1. What is general recombination? What DNA and proteins are required?
2. What is nonreciprocal general recombination? How does it differ from general recombination? (Hint: compare figs. 14.2 and 14.3).
3. What is site-specific recombination? In what context is this likely to occur?
4. Are there any recombination processes that do not require homology? Explain.
5. What is the difference between vertical and horizontal gene transfer?
6. What do the terms exogenote, an endogenote, and merozygote describe? When a linear fragment of DNA that contains some regions homologous to the host chromosome is brought into a cell, what possible fates can befall it?
7. We've looked at plasmids before, but they are so important that we should review their properties here. What is meant by each of the following terms?
   • multiple copy plasmid
     
   • single copy plasmid
     
   • replicon
     
   • episome
     
   • copy number
     
   • “curing” a plasmid
     
   • incompatible plasmids
     
   • virulence plasmids
     
   • metabolic plasmids
     
   • plasmid toxin
     
   • Col plasmid
     
   • bacteriocin
     
   • R factor
     
   • F factor
     
   • conjugative plasmid
     
   • pilus
     
   • rolling circle replication
     
8. Almost all bacterial cells isolated from nature contain one or more plasmids. In laboratory culture plasmids are frequently lost. Are plasmids necessary? Explain.
9. How might you demonstrate the presence of a plasmid in a bacterial cell?
10. What is a transposon? What is an insertion sequence (IS)? Do all transposons have IS? Are enzymes responsible for transposition? If so, where are the genes for them located? Do transposons carry other genes?
11. Compare and contrast plasmids and transposons. How are they similar? How are they different? How are they related?
12. When you have completed the rest of the chapter, be sure you can recognize the differences between transformation, conjugation, and transduction. These are the three mechanisms for gene transfer in bacteria. The remaining questions in this study guide focus on these mechanisms.
13. What is bacterial conjugation? Does it require physical contact between bacteria? What is meant by the terms F⁺, F^-, Hfr, sex pilus?
14. During Hfr conjugation, what determines the origin of gene transfer? For a given Hfr strain, is this order always predictable? Is it efficient? Is there a limit to the amount of DNA that can be transferred?
15. What is an F' plasmid? Is it more similar to an F⁺, Hfr, or F^- state?
16. What is transformation? How efficient is it? What is meant by "competence"? Under what conditions do cells become naturally competent? Can cells that do not possess transformation machinery be transformed? If so, how? Is there a limit to the amount of DNA that can be transferred?
17. What is transduction? What does it accomplish? Is there a limit to the amount of DNA that can be transferred?
18. For now, skip the discussion of lysogeny, temperate phages, and prophages. We'll devote some time to this when we study viruses.
19. In general terms, what is the difference between generalized and specialized transduction?
20. Until the advent of powerful gene sequencing technology in the past decade, the organization of bacterial genomes was studied mainly by conjugation and transduction studies. The single most important experiment was an interrupted mating experiment (see Fig. 14.22). Data such as the graph in Fig. 14.22(b) is used to create maps such as those in Fig. 14.23 (also shown in tabular form in Table 14.4). Examine these figures, with accompanying text, to get a sense of how these techniques work.
21. Look at the genetic map in Fig. 14.23. What is the relationship of this map to the bacterial DNA? How was this map constructed? What to the numbers 0, 10, 20, etc. refer to? Why does the map end at 100?
22. Locate the genes “lac A,Y,Z,O,P”, “argR”, “his G,D,C,B,H,A,F,I,E”, and “argS”. When would they be transferred in a conjugation experiment, relative to “purB”? Why do some genes have multiple letters, while other genes only have a single letter? (Hint: remember operons).