Questions_Cell-CellSignaling - Questions and Answers...

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Unformatted text preview: Questions and Answers for the Cell Cell Signaling Topic 1. You have determined that R. sphaeroides produces an acyl ­homoserine lactone to induce production of the violacin antibiotic in response to quorum sensing. You isolate a mutant strain of R. sphaeroides that is severely defective in producing the violacin and also does not produce the acyl ­homoserine lactone. You hypothesize that the mutant strain has a mutation in the gene for the acyl ­homoserine lactone synthase (a luxI type gene). Before you try to map the mutation, you want to perform one additional test to determine that the defect in violacin production of the mutant strain is due solely to a defect in production of the acyl ­homoserine lactone. Describe this test and the expected results if your hypothesis is correct. 2. You are studying light production from another Vibrio species, V. imagines. You have identified three genes, luxA, luxB, and luxC, that when deleted result in decreased light production, as indicated in the table below. V. imagines also produces an acyl ­HSL that induces light production. The phenotypes of mutants lacking one of the three identified genes are indicated below. What can you conclude about each of the gene products? Gene Deleted in Strains Light Production* Acyl HSL Production# Response to Acyl HSL$ low cell high cell density density low cell density no acyl HSL Wild ­Type 1 10 1 10 1 10 luxA 10 10 10 10 10 10 luxB 1 1 0 0 1 10 luxC 0 0 1 10 0 0 high cell density plus acyl HSL * Light production was measured as the level of light units per cell and was measured for cells that were either at low density or high density. # Acyl ­HSL production was measured as the µM of acyl ­HSL in culture supernatants from cells grown to low or high cell density. $ The response to acyl ­HSL was measured as the level of light units per cell after incubation cells with or with out added acyl ­HSL. Choose all the functions that you can assign to a gene product. (Fill in the blanks with the letters for each function.) Gene luxA _________________________________ luxB _________________________________ luxC _________________________________ Function A. enzyme that produces light B. enzyme that produces acyl ­HSL C. activator protein that induces light production in response to acyl ­HSL D. repressor protein that blocks light production in response to acyl ­HSL 3. From the experiment that demonstrated that there was an extracellular signal that induced light production, can you also conclude that this is not an internal signal that induces light production? 4. The following is an incorrect definition of quorum sensing. Rewrite this sentence to reflect a correct definition. “Quorum sensing is the ability to stop cell growth in response to a high cell density.” ...
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This note was uploaded on 03/06/2012 for the course MIMG 100 taught by Professor Lazazzera during the Summer '10 term at UCLA.

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