Concept explainers
A constitutive mutant is a strain that continuously makes a protein that is inducible in the wild type. Describe two ways in which a change in a DNA molecule could lead to the emergence of a constitutive mutant. How could these two types of constitutive mutants be distinguished genetically?
To discuss:
A constitutive mutant (a strain) can continuously produce a protein molecule that is inducible in the wild type. Describe two ways to produce a constitutive mutant through DNA change. How these two types of constitutive mutants are differentiated genetically.
Concept introduction:
A mutant strain can continuously synthesize a protein because of a mutation in the regulatory gene is known as a constitutive mutant. The regulatory gene is always expressed or not switched off. A strain with a mutation in the lac operon is an example of a constitutive mutant. The lac operon mutation can lead to the transcription of the lac genes in the absence of lactose in the medium.
Explanation of Solution
Formation of a constitutive mutant:
- A constitutive mutant can be produced if the altered repressor protein not able to recognize the operator due to mutation.
- A constitutive mutant can be produced if an operator locus not able to interact with the normal repressor due to mutation.
In both cases, the mutation can lead to continuous production of the protein. The two constitutive mutants can be differentiated genetically by the cis-trans test or a complementation test in merodiploid cells. This test is used to find whether the mutations found in the two mutant strains are in different genes or not.
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Chapter 11 Solutions
EBK BROCK BIOLOGY OF MICROORGANISMS
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- DNA from a strain of bacteria with genotype a+ b+ c+ d+ e+ was isolated and used to transform a strain of bacteria that was a− b− c− d− e−. The transformants were tested for the presence of donated genes. The following genes were cotransformed: a+ and d+ b+ and e+ c+ and d+ c+ and e+ What is the order of genes a, b, c, d, and e on the bacterial chromosome?arrow_forwardT. Miyake and M. Demerec examined proline-requiring mutations in the bacterium Salmonella typhimurium (). On the basis of complementation testing, they found four proline auxotrophs: proA, proB, proC, and proD. To determine whether proA, proB, proC, and proD loci were located close together on the bacterial chromosome, they conducted a transduction experiment. Bacterial strains that were proC+ and had mutations at proA, proB, or proD were used as donors. The donors were infected with bacteriophages, and progeny phages were allowed to infect recipient bacteria with genotype proC− proA+ proB+ proD+. The recipient bacteria werethen plated on a selective medium that allowed only proC+ bacteria to grow. After this, the proC+ transductants were plated on selective media to reveal their genotypes at the other three pro loci. The following results were obtained: Q.Is there evidence that proA, proB, and proD are located close to proC? Explain your answer.arrow_forwardT. Miyake and M. Demerec examined proline-requiring mutations in the bacterium Salmonella typhimurium (). On the basis of complementation testing, they found four proline auxotrophs: proA, proB, proC, and proD. To determine whether proA, proB, proC, and proD loci were located close together on the bacterial chromosome, they conducted a transduction experiment. Bacterial strains that were proC+ and had mutations at proA, proB, or proD were used as donors. The donors were infected with bacteriophages, and progeny phages were allowed to infect recipient bacteria with genotype proC− proA+ proB+ proD+. The recipient bacteria werethen plated on a selective medium that allowed only proC+ bacteria to grow. After this, the proC+ transductants were plated on selective media to reveal their genotypes at the other three pro loci. The following results were obtained: Q.Why are there no proC− genotypes among the transductants?arrow_forward
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