Vector Biology Questions and Answers – Bacteriophages – 1

This set of Vector Biology Multiple Choice Questions & Answers (MCQs) focuses on “Bacteriophages – 1”.

1. Which of the following is not true for a bacteriophage?
a) A very simple structure
b) Consist either DNA or RNA
c) Bacteriophages are viruses
d) Complex structure that infects bacteria
View Answer

Answer: d
Explanation: Bacteriophages are viruses that specifically infect bacteria but these are very simple structures consisting merely of a DNA/RNA molecule surrounded by a protective coat.

2. What is the capsid (protective coat) of the bacteriophage made up of?
a) DNA
b) RNA
c) Protein
d) Organic acids
View Answer

Answer: c
Explanation: The protective coat or capsid is made up of protein molecules which surround the nucleic acid molecule carrying a number of genes including several for the replication of phage.

3. Which of the following is an example of head-and-tail bacteriophage?
a) M13
b) Lambda phage
c) Pbr322
d) M16
View Answer

Answer: b
Explanation: Enterobacteria phage (Lambda phage) infects the bacterial species E.Coli. It consists of an icosahedral head, measuring 50-60 nanometers in diameter and a flexible tail that is around 150 nanometers in length.

4. The replication of phage DNA molecule is associated with which step in the infection cycle of a bacteriophage?
a) First step
b) Second step
c) Third step
d) Preparation stage
View Answer

Answer: b
Explanation: The general pattern of infection, which is the same for all the phages is a three step process. The first step is the attachment of phage to the surface of bacterium and subsequent injection of its DNA into the cell, second step is replication of the injected DNA.

5. The cycle which is completed quickly in the infection by a phage is ________
a) Lysogenic
b) Lytic
c) Replication
d) Capsid formation
View Answer

Answer: b
Explanation: With some phage types the entire infection cycle is completed very quickly, possibly in less than 20 minutes. This type of rapid infection is called a lytic cycle, as a release of the new phage particles is associated with lysis of the bacterial cell.
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6. Which is a reason of instability of phage DNA molecule in the host cell in a lytic cycle?
a) The huge size of phage DNA
b) Inability of replicative enzymes
c) Immediate synthesis of capsid
d) Lytic cycle inefficiency
View Answer

Answer: c
Explanation: The characteristic feature of a lytic infection cycle is that phage DNA replication is immediately followed by synthesis of capsid proteins and the phage DNA molecule is never maintained in a stable condition in the host cell.

7. Which infection cycle is characterized by retention of the phage DNA molecule in the host bacterium for many thousands of cell division?
a) Lysogenic cycle
b) Lytic cycle
c) Integrative Phase
d) Protein synthesis
View Answer

Answer: a
Explanation: With many lysogenic phages the phage DNA is inserted into the bacterial genome in a manner similar to episomal insertion. The integrated form of the phage DNA is called the prophage and bacterium is referred to as a lysogen.

8. Which of the following statements is not true in the context of infection by an M13 phage?
a) Lytic phage
b) Lysogenic phage
c) New phage particles are continually synthesized
d) The DNA is not integrated in host genome
View Answer

Answer: a
Explanation: M13 is a lysogenic phage that follows a different infection cycle when M13 infects a bacterium, new phage particles are assembled and released continually from the cell. There is no integration of phage DNA into the bacterial chromosome and lysis of the cell also never occurs.

9. Approximate size of lambda phage is _______
a) 23 kb
b) 100 kb
c) 49 kb
d) 12 kb
View Answer

Answer: c
Explanation: Lambda phage is extensively used as a cloning vector. The lambda DNA molecule is 49 kb in size and has been intensively studied by the techniques of gene mapping and DNA sequencing.

10. What are sticky ends?
a) Ends of M13 vector
b) 12 nucleotide stretch in lambda phage
c) The replicated product phage DNA
d) Ends on two sides of origin
View Answer

Answer: b
Explanation: At either end of the lambda DNA molecule is a short 12 nucleotide stretch in which the DNA is single stranded. The two single strands are complementary and base pair with each other to form a circular completely double stranded molecule.

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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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