Submitted by: Submitted by rr426
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Category: Science and Technology
Date Submitted: 11/07/2012 05:03 AM
Experiment 3: Characterization of Nonsense Mutations in E.Coli
A. Purpose:
a. This experiment was conducted with lac- mutants mated with F- strains with a lac-pro deletion region with different amber suppressors. These matings were then tested to determine if the amber suppressors of the F-strains suppress the nonsense mutations on the lac- mutants. Each amber suppressor gene recognizes the stop codon UAG and inserts a amino acid to restore function of the protein.
B. Controls:
a. The controls are lac- strain on min +strep and min+nal plates, CSH54 on min+strep plate, CSH55 on min+nal plate, and CSH56 on min+nal plate. The controls are used to test if the strains do indeed contain the correct properties.
b. The lac- strain has proline but is sensitive to nalixidic acid and streptomycin. Hence, there should no growth on the control plates for lac- mutants. The CSH54 strain is resistant to streptomycin but lacks proline and lactose. So though it may be able to survive in the antibiotic environment on the min+strep plate, it should not grow due to its lack of proline. The CSH55 and CSH56 strains also lack the proline-lactose region but both are resistant to nalidixic acid. Thus, there should be no growth on the min+nal plate because both strains lack the proline gene.
c. The lac- mutant and the CSH54 control plate did not exhibit any growth. The CSH55 and CSH56 strains exhibited 15 and 7 colonies, respectively. This growth could be due to the fact that the CSH55 and CSH56 strains have a semi-functional lac gene.
C. Results:
Table 1. Matings on Min + Lactose plate
Mating Observations
F (lac- with CSH54) No growth
E (lac- with CSH55) No growth
D (lac- with CSH56) No growth
Lac+ control White colony
Lac- control No growth
Table 2. Matings on MacConkey’s Agar.
Mating Observations
F (lac- with CSH54) 8 white colonies
E (lac- with CSH55) 6 white colonies
D (lac- with CSH56) 6 white colonies
Lac+ control 1 purple colony
Lac- control 1 white...