Genetic Engineering Multiple Choice Questions on “BAC Vector, M13 and its Derivatives – 1”.
1. F (fertility) factor is used in many bacterial systems for different purposes. Choose the incorrect statement with respect to the F factor.
a) It was identified in E. coli for catalysing genetic exchange between cells
b) Cells having F factor are called as female
c) The F factor is transferred from one cell to another via factors present outside
d) They are not related to BAC systems
Answer: a
Explanation: BAC vectors are based on the F (fertility) factor. They are known for transferring genetic material between cells and they do it by a proteinaceous filament called sex pilus. The cells having F factor are called as male cells.
2. F factor integration into the host chromosome is called as __________
a) F’ plasmid
b) F factor and host chromosome recombination
c) Hfr (High frequency of recombination)
d) Recombinant host chromosome
Answer: c
Explanation: F factor integration can be done into the host chromosome and this is called as Hfr (High frequency of recombination) strain.
3. Excision of the F factor can also be done from the host chromosome. Choose the incorrect statement in respect to it.
a) This excision is possible in vivo
b) Along with the F factor, host chromosome’s DNA sequences are also excited
c) The sequences of host chromosome which can be accommodated in the F plasmid are small in size
d) These plasmids are termed as F’ plasmids
Answer: c
Explanation: It is possible to carry out the excision of the F factor from the host chromosome. The excision is possible in vivo. Along with the F factor, the DNA sequences of host chromosome are also excised. The F plasmid is able to accommodate very large size f host chromosome fragments and these are known as F’ plasmids.
4. The low copy number of F plasmid is essential for the stability of these plasmids.
a) True
b) False
Answer: a
Explanation: Usually, the F plasmids are present in a low copy number in cells. These low copy numbers are very essential for the stability because then only a few molecules can act as substrates for recombination mediated deletion.
5. Choose the correct statement for BAC vector system.
a) BAC vector system stands for bacteria and chromosome
b) It usually accepts insert of size approximately 1000kbp
c) The repE and oriS sequences are required for controlling the copy number and par A-C sequences are required for replication
d) A selectable marker is there for chloramphenicol resistance
Answer: d
Explanation: BAC vector system stands for Bacterial Artificial Chromosome. It accepts an insert of size 100kbp-300kbp. The repE and oriS sequences are required for controlling the replication and the par A-C sequences are required for controlling the copy number. A selectable marker is there for chloramphenicol resistance. A lacZ gene is also present and recombination of BAC vectors is done into E. coli by electropoartion.
6. The bacteriophage M13 vectors belong to a group of phages called as __________
a) skinny or filamentous phage
b) M phage group
c) single stranded phage
d) double stranded phage
Answer: a
Explanation: Bacteriophage M13 vectors belong to a group of vectors known as skinny or filamentous phage. They have a dimension of 850 nm * 6 nm * 6nm. They are very useful as they convert the double stranded DNA into single stranded DNA.
7. Choose the correct statement for the infection process of M13.
a) The infectious particle is double stranded
b) It is contained in a protein coat which is made up of products of gene III or gene VIII
c) The phage infects only female cells
d) The phage enters the bacterial cells by the filament which is meant for movement
Answer: b
Explanation: M13 infectious particles are single stranded in nature. It is contained in a protein coat which is made up of products of gene III or gene VIII. The phage infects the bacterial cells by sex pilus and thus it infects only male cells.
8. Once the bacteriophage enters the bacterial cells, some changes are carried out in it. Which of the following is not included?
a) The single stranded molecule entering the cell is single stranded and is called as a + strand
b) The single stranded molecule is converted into double stranded molecule which is called as replicative form (RF)
c) It is carried out in a process similar to normal replication process of E. coli
d) The positive strand is used for the transcription of viral proteins
Answer: d
Explanation: Once the bacteriophage enters the bacterial cells it is converted into double stranded form from the single stranded form. The double stranded form is known as replicative form (RF). The single strand enteri g is called as a + strand. It is carried out in a process similar to that the normal replication process. A specific origin of synthesis is used for transcription of the complementary negative strand. The minus strand can be used to synthesize viral proteins.
9. Replication can also be carried out by rolling circle replication. Choose the correct statement for this type of replication?
a) It can be used for the formation of RF
b) The product of gene III binds on a specific site of double stranded genome
c) It creates a nick in the – strand generating a free 3’ hydroxyl
d) This strand is extended by the polymerase and displaces the original – strand
Answer: a
Explanation: Rolling circle replication is used for the formation of RF. The product of gene II binds on a specific site of double stranded genome. It creates a nick in the + strand generating a free 3’ hydroxyl. This strand is extended by the polymerase and it displaces the original + strand. This strand is removed from the newly synthesized strand because of another nick by gene II. Thus a separate + strand is created and it is circularized by gene II product.
10. Gene V blocks the production of which gene?
a) Gene III
b) Gene II
c) Gene VIII
d) Gene IV
Answer: b
Explanation: Gene V blocks the production of gene II. As the gene V blocks the production of gene II, conversion of single strands into double strands is also blocked.