This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Viruses of Bacteria – Lysogeny and Lytic”.
1. What does a viral DNA becomes after being associated with the bacterial chromosome?
Explanation: In lysogeny the viral DNA of the temperate phage, instead of taking over the functions of the cell’s genes, is incorporated into the host DNA and becomes a prophage in the bacterial chromosome, acting as a gene.
2. In which of the following method, the viral particles are transmitted through lysis of cell?
a) Lytic cycle
Explanation: In the lytic cycle after the infection of bacterial cells by phages, the viral particles are transmitted through lysis of cell and finally terminates.
3. repressor protein makes the cell resistant to lysis.
Explanation: The temperate phage possesses a gene that codes for a repressor protein which makes the cell resistant to lysis initiated either by the prophage or by lytic infection by other viruses. The multiplication of the phage is repressed and lysogenization occurs.
4. Which of the following is the characteristic of repressor protein?
a) basic protein
b) acidic protein
c) basic protein, molecular weight of 26000
d) acidic protein, molecular weight of 26000
Explanation: The repressor protein is an acidic protein with a molecular weight of 26000. It has been isolated from lambda phage and purified.
5. cro gene is an example of an immunity repressor.
Explanation: Upon infection by lambda phage, the phage cro gene is transcribed, resulting in the synthesis of a protein repressor that inhibits the synthesis of the immunity repressor.
6. Which of the following gene codes for an enzyme which directs the insertion of the phage DNA into the bacterial chromosome?
a) recA gene
b) cro gene
c) int gene
d) gal gene
Explanation: A lambda phage enzyme, coded by the int gene, directs the insertion of the phage DNA into the bacterial chromosome. It catalyzes a single site-specific recombination event, resulting in the insertion of the phage DNA into the cell genome.
7. Which of the following phage do not cause lysogeny?
Explanation: Phages like T2 that do not cause lysogeny are termed virulent. Phages produced by lysogenic strains are termed temperate phages, and the relationship between the phage and the bacterium is termed lysogeny.
8. The protein integrase is encoded by which of the following gene?
a) gal gene
b) lambda gene
c) bio gene
d) cro gene
Explanation: Integration of the lambda chromosome requires the action of a protein termed integrase encoded by a lambda gene and occurs at a 13 base pair region of DNA sequence homology between the bacterial and phage chromosomes.
9. In which of the following phage prophage exists as a circular form?
a) Phage lambda type
b) Phage P1 type
c) Phage T2 type
d) Phage T1 type
Explanation: In lysogeny of the P1 type, viral DNA does not normally become integrated into the host chromosome. Instead the prophage exists as a circular, self-replicating, double-stranded DNA element termed a plasmid.
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