This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Plasmid DNA Replicates by Two Alternative Methods – 2”.
1. In which phase bacteria develop competence?
a) Late phase
b) Log phase
d) Lag phase
Explanation: Bacteria develop competence during the late phase of their growth cycle. In this cycle the density of bacteria is high but the cell division stops.
2. In which bacteria competence pheromones was first identified?
a) S. pneumoniae
b) B. subtilis
c) H. influenzae
d) N. gonorrbacae
Explanation: Bacillus subtilis contain small peptides called competence pheromones that are secreted by cells and accumulate at high cell density. High concentration of these pheromones induces the expression of genes encoding proteins required for facilitating the process of transformation.
3. What is the percentage of DNA molecules taken up by competent cells during transformation?
Explanation: The DNA molecules taken up by competent cells during transformation are usually only about 0.2 – 0.5% of the complete genetic material. Thus plasmids for recombination are thus prepared to maintain the size of the adequate molecule to be taken up by the bacterium.
4. Transformation of E. coli does not occur.
Explanation: E. coli is the most intensely studied bacterial species under natural conditions. In 1946, Joshua Lederberg and Edward Tatum discovered that E. coli cells transfer genes by conjugation thus exhibiting transformation.
5. During conjugation the Donor cell have cell surface appendages known as ____________
a) F pili
b) B pili
c) A pili
d) D pili
Explanation: During conjugation Donor cells have cell surface appendages known as F pili. The synthesis of these F pili is controlled by gene present on a plasmid called the F factor or the fertility factor.
6. What is the size of the F factor that is involved in conjugation?
a) 106 base pairs
b) 105 base pairs
c) 10-12 base pairs
d) 109 base pairs
Explanation: Most F factors are approximately 105 base pairs in size. This contains the gene that facilitates the growth if the F pili through which the bacteria is able to transfer the F factor to another bacteria.
7. In how many states the F plasmid can occur within bacteria?
Explanation: The F plasmid can occur within bacteria in two states. They are the autonomous or plasmid state or the integrated state within the bacterial genome.
8. By which of the following methods does the F plasmid integrates into the bacterial genome?
Explanation: The F-factor can integrate into the bacterial chromosome by site specific recombination. This recombination is mediated by short stretches of homologous sequence in the genome and plasmid of the bacteria.
9. High frequency recombination cell contain an integrated F factor. What is the name of such a cell?
a) Har cell
b) Hra cell
c) Hfr cell
d) Hrf cell
Explanation: High frequency recombination cell contain an integrated F factor. These cells are known as Hfr cell. F factor mediates the transfer of chromosome from the Hfr+ cell to an Hfr- cell transforming it into an Hfr+ cell.
10. What is the strain of the Hfr+ cell where the F factor is integrated near the tbr and leu loci?
a) Hfr H
b) Hfr A
c) Hfr B
d) Hfr K
Explanation: The particular strain of the Hfr+ cell where the F factor is integrated near the tbr and leu loci is the Hfr H cell. In this strain the transfer of F factor induces the transfer of the other two genes with it.
11. Transformation, transduction and conjugation occurs in every bacterial cell.
Explanation: Transduction is the only process that occurs in all bacteria. The occurrence of conjugation and transformation depend on whether the required genes and metabolic machinery have evolved in that species of the bacterium or not.
Sanfoundry Global Education & Learning Series – Molecular Biology.
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