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PROBLEM_SET_3.466n_Lec19-21 - b When a partial diploid is...

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Genetics 466 Fall 2008 Sean Carroll 1 PROBLEM SET #3 (lectures 19-21) 1. You should be familiar with the following terms and concepts: promoter β -galactosidase attenuation operator permease polycistonic mRNA repressor constitutive synthesis cAMP operon inducible synthesis cAMP receptor protein inducer transcriptional control trp operon co-repressor lytic cycle early and late genes lactose cis;trans effects genetic switch merozygote lysogeny cro, cI cII, cIII, N, Q glucose feedback Lex A, rec A 2. What are the physical and biological consequences of lac repressor binding to the lac operator? 3. Is β -galactosidase made and is lac mRNA synthesis inducible, constitutive, or neither in cells of the following genotypes? lacO c lacZ - lacY + /lacZ + lacY + lacP - lacZ + /lacO c lacZ - lacI + lacP - lacZ + /lacI - lacZ + Why? 4. A mutant strain of E. coli is found that makes both β -galactosidase and permease whether lactose is present or not. a. What are two possible (haploid) genotypes of this mutant?
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Unformatted text preview: b. When a partial diploid is formed with an F1 plasmid carrying a wild-type lac operon, synthesis becomes inducible. What was the genotype of the mutant? 5. Certain mutants of the lacI repressor gene do not bind lactose but do bind to the operator. In these strains, do you think β-galactosidase synthesis is inducible or constitutive, or neither? 6. Certain bacteria are known that metabolize crude oil. How would you test whether the enzymes that break down the oil are constitutive or inducible? 7. How does bacteriophage lambda decide whether to grow lytically or to lysogenize a newly infect host? What are the roles of the cI, N, and cro proteins in these decisions? What about cll? 8. What are the properties expected of mutants in cI, N, cro, and cII with respect to the propensity for lytic growth or lysogeny? Why? 9. Why do cIII mutants fail to lysogenize?...
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