Genetics: From Genes to Genomes
6th Edition
ISBN: 9781259700903
Author: Leland Hartwell Dr., Michael L. Goldberg Professor Dr., Janice Fischer, Leroy Hood Dr.
Publisher: McGraw-Hill Education
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Chapter 14, Problem 32P
Scientists who study amino acid biosynthesis pathways want to isolate auxotrophic bacteria. A technique called penicillin enrichment makes this task easier. This procedure starts by exposing a liquid culture of wild-type (prototrophic) bacteria growing in rich (complete) medium to a chemical mutagen. After this treatment, the cells are centrifuged to remove the liquid and the mutagen. The pellet of cells at the bottom of the centrifuge tube is now resuspended in medium that lacks one amino acid (in this example, cysteine) but contains penicillin. Subsequently, the bacteria are poured onto a filter that concentrates them and allows them to be washed free of the penicillin. The living bacteria retained on the filter are highly enriched for cysteine auxotrophs.
| a. | Given what you know about the action of penicillin, explain why this enrichment occurs. |
| b. | Penicillin enrichment is not a selection, because the drug does not kill 100% of the prototrophs. The cells on the filter thus need to be screened for cysteine auxotrophy. How would the scientists perform this screen? |
| c. | If the starting strain contained a pen gene on a plasmid, would this scheme still enrich for auxotrophs? Explain. |
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You are studying the tryptophan synthetase gene that Yanofsky also examined to determine the relationship between the nucleotide sequence and the amino acid sequence of the gene. Yanofsky found a large number of mutations that affected the tryptophan synthetase gene.
A) If you took this mutant E. Coli line (that has an Arginine at this location) and exposed it to a mutagen that could potentially change bases, what are the second mutations you would most likely discover that would restore the activity of the tryptophan synthetase gene and where would it be located?
B) Most of the mutations that Yanofsky recovered were missense mutations. However, Yanofsky also recovered a nonsense mutation that changed amino acid number 15 into a stop codon. This codon normally encodes Lysine. Does the recovery of this mutation support the hypothesis that this Lysine residue is critical in the function of the tryptophan synthetase protein?
What would be the most likely effect of a mutation at the following locations in an E. coli gene? a. -8 b. -35 c. -20 d. Start site
You have isolated several E. coli mutants: Mutant #1 has a point mutation in the -10 region of the promoter of a structural gene encoding an enzyme needed for synthesis of the amino acid serine. Mutant #2 has a mutation in the -35 region in the promoter of the same gene. Mutant #3 is a double mutant with mutations in both the -10 and -35 region of the promoter of the same gene. Only Mutant #3 is unable to make serine. Why do you think this is so?
Chapter 14 Solutions
Genetics: From Genes to Genomes
Ch. 14 - Choose the phrase from the right column that best...Ch. 14 - The unicellular, rod-shaped bacterium E. coli is 2...Ch. 14 - Now that the sequence of the entire E. coli K12...Ch. 14 - Bacterial genomes such as that of E. coli...Ch. 14 - List at least three features of eukaryotic genomes...Ch. 14 - Describe a mechanism by which a gene could move...Ch. 14 - High salt concentrations tend to cause protein...Ch. 14 - Recently, scientists tested the possibility that...Ch. 14 - A recent metagenomic study analyzed the...Ch. 14 - Linezolid is a new type of antibiotic that...
Ch. 14 - A liquid culture of E. coli at a concentration of...Ch. 14 - Pick out the medium i, ii, iii, or iv onto which...Ch. 14 - This problem concerns Fig. 14.14, which...Ch. 14 - In two isolates one is resistant to ampicillin,...Ch. 14 - E. coli cells usually have only one copy of the F...Ch. 14 - In E. coli, the genes purC and pyrB are located...Ch. 14 - DNA sequencing of the entire H. influenzae genome...Ch. 14 - Genes encoding toxins are often located on...Ch. 14 - a. You want to perform an interrupted-mating...Ch. 14 - In Problem 19, do you think that most of the...Ch. 14 - One issue with interrupted-mating experiments such...Ch. 14 - Prob. 22PCh. 14 - Starting with an F- strain that was prototrophic...Ch. 14 - You can carry out matings between an Hfr and F...Ch. 14 - Genome sequences show that some pathogenic...Ch. 14 - Generalized and specialized transduction both...Ch. 14 - This problem highlights some useful variations of...Ch. 14 - A researcher has a Trp auxotrophic strain of E....Ch. 14 - Streptococcus parasanguis is a bacterial species...Ch. 14 - The sequence at one end of one strand of the...Ch. 14 - Scientists who study amino acid biosynthesis...Ch. 14 - Suppose that you could obtain radioactively...Ch. 14 - Prob. 34PCh. 14 - Some scientists are trying to engineer...
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