Vector Biology Questions and Answers – Bacteriophages – 2

This set of Vector Biology Question Bank focuses on “Bacteriophages – 2”.

1. What is the function of a tail of the head-and-tail lambda phage?
a) Stabilization of phage DNA
b) Attachment of phage
c) Release of replicative enzymes
d) Helps in motility
View Answer

Answer: b
Explanation: The DNA is contained in the polyhedral head structure and the tail serves to attach the phage to the bacterial surface and to inject the DNA into the cell.

2. How are genes arranged in a lysogenic phage (for example a lambda phage)?
a) Alternatively
b) In clusters
c) On opposite ends
d) Similar genes at distant positions
View Answer

Answer: b
Explanation: Genes related in terms of function are clustered together in the genome. Clustering is profoundly important for controlling the expression of the lambda genome as it allows genes to be switched on and off rather than individually.

3. Circularization of the injected linear phage DNA molecule is facilitated by which of the following?
a) Polyhedral head
b) Cos sites
c) Phage tail
d) Capsid proteins
View Answer

Answer: b
Explanation: The lambda cohesive ends are called the cos sites and they play different roles during the infection cycle. They allow the linear DNA molecule that is injected into the cell to be circularized, which is a necessary prerequisite for insertion into the bacterial genome.

4. By which mechanism does the replication of new lambda DNA molecules are produced in the host bacterium?
a) Rolling Circle Mechanism
b) DNA Polymerase Binding
c) The same mechanism as that of host
d) Replication fork propagation
View Answer

Answer: a
Explanation: A large number of new lambda DNA molecules are produced by the rolling circle mechanism of replication, in which a continuous DNA strand is rolled off the template molecule.

5. M13 filamentous phage DNA molecule is smaller than the head-and-tail lambda phage.
a) True
b) False
View Answer

Answer: a
Explanation: M13 DNA molecule is much smaller than the lambda DNA molecule, being only 6407 nucleotides in length. It is circular and consists entirely of single stranded DNA.
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6. Which of these is not a feature associated with M13 phage?
a) Doesn’t need genes for insertion into host genome
b) Capsid constructed of multiple copies of 3 genes
c) Simpler infection cycle than lambda
d) Capsid constructed of 15 different proteins
View Answer

Answer: d
Explanation: The small size of M13 DNA molecule means that it has a room for fewer genes and this is possible because the M13 capsid is constructed from multiple copies of just 3 proteins (3 genes) whereas synthesis of lambda phage capsid involves 15 different proteins.

7. How does an injection of a filamentous phage (example- M13) DNA into the host bacterium occur?
a) Via pilus
b) Surface attachment
c) Transformation
d) Transfection
View Answer

Answer: a
Explanation: Injection of an M13 DNA molecule into an E.coli occurs via pilus, the structure that connects two cells during sexual conjugation. Once inside the cell, single stranded molecule acts as the template for synthesis of the complementary strand.

8. Replicative form (RF) refers to what part of the M13 bacteriophage?
a) M13 genome
b) Restriction sites
c) Endonuclease activity
d) Replication phase
View Answer

Answer: a
Explanation: The double-stranded form of M13 genome is known as the Replicative form, which behaves much like a plasmid; this is what makes it an attractive cloning vector.

9. Phage display technique makes use of which of the following vectors?
a) M13
b) Lambda
c) 2 micron circle
d) BAC
View Answer

Answer: a
Explanation: M13 vectors are used for phage display, a technique for identifying genes whose protein products interact with one another. M13 is also used in DNA sequencing and in vitro mutagenesis.

10. Which of the following is a positive regulatory gene on the lambda phage genome?
a) N
b) O
c) P
d) R
View Answer

Answer: a
Explanation: Except for the two positive regulatory genes N and Q, all functionally related genes are clustered together on the phage lambda genome map.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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