This set of Genetic Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Bacteriophage-Mu and Bacteriophage-Pi”.
1. Bacteriophage Mu is also a phage, choose the correct statement for it.
a) It is an example of temperate phage
b) It is packaged into heads containing 50 kbp of DNA
c) When the phage replicates it goes transposition only a few times
d) Mu can’t be used for cloning in vivo
View Answer
Explanation: Bacteriophage Mu is also a phage, it is an example of temperate phage. It is packaged into heads containing 39 kbp of DNA. When the phage replicates it goes transposition a few hundred times and inserts itself into many places in the host genome. Mu can be used for cloning in vivo as a ‘mini Mu’ that contains reduced phage genome.
2. Choose the incorrect statement for ‘Mini Mu’?
a) It is produced by cloning of bacteriophage Mu in vivo
b) It contains reduced phage genome
c) It doesn’t contain replication of origin of plasmid
d) A selectable marker is added
View Answer
Explanation: Mini Mu is produced by cloning of bacteriophage Mu in vivo. It is having reduced phage genome. A selectable marker and an origin of replication of plasmid are added.
3. Which of the following is not included as a step for cloning mini Mu in vivo?
a) A culture of target strain, whose DNA we want to clone is infected with mini Mu
b) The phage is inserted at multiple sites in the genome
c) Some of the packaged strain is flanked by two mini Mu genes
d) The packaged phage is introduced into a second strain and Mu would replicate as a phage
View Answer
Explanation: For cloning in mini Mu, a culture of target strain whose DNA we want to clone is infected with mini Mu. The phage is inserted at multiple sites in the genome. Some of the packages strain is flanked by two mini Mu genes. The packaged phage is introduced into a second strain and the Mu won’t be able to replicate as a phage.
4. If recombination takes place between elements in the second strain, it would replicate by the origin of replication of mini Mu.
a) True
b) False
View Answer
Explanation: If recombination takes place between elements in the second strain, it would replicate as a plasmid by the origin of replication of mini Mu. Thus a plasmid is formed with a piece of DNA from first strain and stably maintained in the second strain.
5. Which of the following is a restriction for cloning in bacteriophage Mu?
a) It is limited to handling only small number of phage particles
b) It relies on whether the DNA is flanked by two mini Mu genes or not
c) Recombination between the elements in the second strain is not a restriction
d) Fragments of any genomic DNA can be cloned irrespective of the fact whether or not the phage can replicate in it or not
View Answer
Explanation: The cloning in bacteriophage Mu is restricted by some factors. These include, it depends whether the DNA is flanked by two mini Mu genes or not. Recombination between the elements in the second strain is also important. Fragments of only those genomic DNA can be cloned, in which Mu can replicate.
6. What is the size of the insert that can be accommodated in the head of bacteriophage PI?
a) 30-40 kbp
b) 80-95 kbp
c) 110-115 kbp
d) 200-300 kbp
View Answer
Explanation: Bacteriophage PI is known to accommodate the larger size of fragments. The size of the fragments that can be accommodated in the head of this phage lies between 110-115 kbp.
7. What is the function of the pac site in the bacteriophage PI?
a) It is responsible for the initiation of packaging
b) It is responsible for the termination of packaging
c) It is responsible for the initiation of replication
d) It is responsible for the termination of replication
View Answer
Explanation: The pac site in the bacteriophage PI is responsible for initiating the packaging of DNA into the phage heads.
8. What is the function of loxP sites?
a) It is responsible for linearization of DNA in the host bacterium
b) It is responsible for circularization of DNA in the host bacterium
c) It is responsible for conversion of single stranded DNA into double stranded DNA
d) It is responsible for conversion of double stranded DNA into single stranded DNA
View Answer
Explanation: The lox P sites are responsible for the circularization of the linear DNA molecules in the host bacterium.
9. Which of the following is not included as a step in cloning in bacteriophage PI?
a) The growth of vector is done as a plasmid by using pBR322 origin of replication
b) Cleaving with BamH1 is done and then products cleaved with Sau3A are ligated
c) Incubation with mutant lysogen is done which doesn’t cleaves the recombinants at pac sites
d) Incubation is done with mutant lysogen which doesn’t contains head and tail proteins
View Answer
Explanation: Bacteriophage PI is a complex vector. The growth of vector is done as a plasmid by using pBR322 origin of replication. Cleaving with Bam H1 is done and it is followed by ligation with Sau3A partial digestion products. It is followed by incubation with mutant lysogen which cleaves the recombinants at pac sites but there are no head and tail proteins. It is followed by incubation in lysogen in which cleavage is not carried out at pac sites but there are head and tail proteins. It leads to packaging into heads.
10. What happens after packaging is carried out in the phage head?
a) A sequence dependent cleavage of DNA is carried out
b) A sequence independent cleavage of DNA is carried out
c) They are linearized before they are infected into the bacterial cells
d) They are circularized before they are infected into the bacterial cells
View Answer
Explanation: After the packaging is carried out in the phage head, a sequence independent cleavage of DNA is carried out. Molecules with a very small size insert can’t fill into the whole phage head before the next pac site is reached.
11. Circularization must take place in the bacterial cells before the replication starts.
a) True
b) False
View Answer
Explanation: Circularization must take place in the bacterial cells before the replication is initiated. The cells are introduced into the bacterial cells after the packaging has been carried out.
12. How many origins of replication are there once the cyclization is carried out by loxP sites?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: There are two origins of replication once the cyclization is carried out by loxP sites. One origin of replication is for low copy number and the other can be activated for carrying out a high copy number replication.
13. Choose the incorrect statement for PAC vectors.
a) In these vectors, the phage packaging signals are removed but the two P1 origin of replication persist
b) They resemble BAC vectors
c) They accept an insert of upto 300 kbp
d) Instability is observed
View Answer
Explanation: PAC vectors are those vectors, in which the phage packaging signals are removed but the two P1 origin of replication persist. These resemble BAC vectors. They accept upto an insert of upto 300 kbp. Maintenance at low copy numbers is helpful in avoiding instability.
14. Choose the correct statement in respect to sacB gene?
a) The cloning site for PAC lies on the side of sacB gene
b) It is responsible for producing an enzyme which is responsible for catalysing sucrose into glucose and fructose
c) Expression of sacB in the presence of sucrose is beneficial
d) Levan is non-toxic for E. coli
View Answer
Explanation: sacB gene along with E. coli promoter flanks the cloning site in PAC vector. It is responsible for producing an enzyme which is responsible for catalysing sucrose into glucose and fructose. The fructose is ploymerized to levan and is toxic to E. coli. Thus expression of sacB in the presence of sucrose is lethal.
15. Selection of molecules by lack of inserts on the basis of the sacB gene is known as:
a) positive selection
b) negative selection
c) counter selection
d) sacB selection
View Answer
Explanation: The sacB gene is abolished if an insert is there in the cloning site and thus can survive in the presence of sucrose. It is known as a positive selection if it is directly looked for an insert. If instead of insert, absence of sacB gene is looked upon, it is called as the counter selection.
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