Question

Pseudomonas has a plasmid containing the mer operon, which includes a gene for mercuric reductase. The enzyme catalyzes the reduction of the mercuric ion Hg²⁺ to the uncharged form of mercury, Hg⁰ Hg²⁺ is quite toxic to cells, Hg⁰is not.

1. What condition would induce this operon to be transcribed and the transcript to be translated into the proteins including mercuric reductase?

2. The protein encoded by the mer operon binds to Hg²⁺ outside the cell and brings it into to the cell, why would a cell bring in a toxin?

Two daughter cells are most likely to inherit which one of the following from a parent cell?

3. a change in a nucleotide in mRNA, tRNA or rRNA?

4. Which of the following is NOT a method of horizontal gene transfer? Contrast two methods of horizontal gene transfer.

conjugation, integration of a transposon, transduction or transformtion

PLEASE ANSWE ALL

Answer 1

1. The plasmid of Pseudomonas contains mer operon and genes encoding mercuric reductase. The operon is induced by the inducer. In this case, the inducer is mercury ions. in presence of mercury ions, the operon is active and transcription of genes is carriedout. T hen the genes transcribed produce the required proteins through translation.

2. The protein encoded by mer operon binds the Hg²⁺ ions outside the cells and are brought inside the cells. The Hg²⁺ ions are toxic to cells but, Pseudomonas is able to convert Hg²⁺ ions back to Hg and mercury shows some benefits on Pseudomonas cells.

3. Mutation is a sudden heritable change and this change shoud occur in nucleotide of DNA that may be inherited from parent to daughter cells. Moreover, the nucleotide change also results in cange in mRNA sequence and change is protein to be synthesized.

4. Horizontal gene transfer is a method of transfer of genes of one organism into another. These is mostly observed in bacteria through genetic recombination methods such as conjugation, transformation, transduction and insertion of a transposon. Transformation is uptake of naked DNA from surroundings. Conjugation takes place between F⁺ and F^- strains. A copy of plasmid from F⁺ cells is transferred into F^- cell through conjugation tube and then both cells contain the plasmid.