This set of Vector Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cloning Vectors Based on Phages”.
1. To which organism does bacteriophage lambda belong?
b) Bacillus subtilis
c) Escherichia coli
d) Saccharomyces cerevisiae
Explanation: Bacteriophage lambda is genetically complex but very extensively studied virus of E.coli. Because it has been the object of so much research in molecular genetics, it was natural that, right from the beginnings.
2. What is the confirmation of lambda phage DNA when it is isolated from the phage particle?
b) Open circular
d) Linear duplex
Explanation: The phage DNA molecule, unlike the bacterial plasmid DNA, exists usually in a linear conformation and DNA is a duplex molecule.
3. Who determined the sequence of Lambda phage?
b) Maxam Gilbert
d) John Williams
Explanation: The exact sequencing of lambda phage of 49 kb was done with Sanger sequencing method in 1982. The principle of the method was chain termination.
4. What form does the phage DNA take when it is injected into the host?
c) Double helical
Explanation: There are 12 bp long overhangs present at each end of the phage DNA which are complementary to each other and result in its circularization upon insertion into the host.
5. Which region of the phage genome is not essential for growth?
a) Between N and Q genes
b) Cohesive sites
c) Recombination and lysogenization
d) Host lysis
Explanation: The recombination and lysogenization region are non-essential for the growth of phage inside the host molecule. This region hence can be replaced with foreign DNA.
6. What is the role of phage cI gene?
a) Host lysis
b) Dormancy and immunity
c) Gene regulation
d) Temperature regulation
Explanation: A phage may convert to a dormant lifestyle inside the host that is switching to becoming a prophage rather than causing a lytic infection. The product of the phage cI gene is responsible for conferring dormancy and immunity to superinfection.
7. What is the function of early gene regulation?
c) Lytic cycle
d) Cohesive site formation
Explanation: The early gene transcription establishes the lytic cycle in competition with lysogeny. In the lytic cycle, lambda transcription occurs in three phases.
8. What is the function of late gene regulation?
a) Packaging DNA
b) Host lysis
c) Host infection
Explanation: In the lambda lytic cycle there are three temporal stages: early, middle and late. Late is responsible for packaging the DNA into mature phage particles.
9. The cI gene is of what type?
d) Silent gene
Explanation: The cI gene is a repressor gene. Following infection, early transcription proceeds from major promoters situated to the left and right of the cI gene.
10. What is the role of N and Q genes?
a) Positive regulation
b) Negative regulation
c) Transcription initiation
d) Transcription termination
Explanation: Both N and Q pay positive regulatory roles essential for phage growth and plaque formation. But an N-negative phage can produce a small plaque if the termination site is removed.
11. When was bacteriophage discovered?
Explanation: Virus that infects bacteria is known as a phage and was discovered by Fredrick in Britain (1915) and Felix in France (1917).
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