This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Ti Plasmids are Transferred from Bacteria to Plants – 2”.
1. The main problem in the formation of the chimera Ti plasmid is _____________
a) It is unstable
b) Large size
c) High virulence
d) No unique restriction site
Explanation: The main problem is that a unique restriction site is impossibility with a plasmid 200 kb in size. Novel strategies have to be developed for inserting new DNA into the plasmid.
2. The binary vector strategy uses two different vectors for the production of the single chimera molecule by recombination.
Explanation: The co-integration strategy uses an entirely new plasmid, based on an E. coli vector, but carrying a small portion of the T-DNA. The homology between the new molecule and the Ti plasmid means that if both are present in the same A. tumefaciens cell, recombination can integrate the E. coli plasmid into the T-DNA region.
3. Which of the following does not play any role in the infection of plant cell by the Ti plasmid of A. tumefaciens?
b) Virulence region
c) Host specificity region
d) 25 base pair repeats
Explanation: The host specificity region is required for the specificity of the cells to be infected. Virulence region is required for infection of the cells. The 25 base pair repeats are required for the transfer of the T-DNA from the bacterial cell to the plant cell. The T-DNA causes the cancer but plays no role in the process of infection.
4. Disarming of Ti plasmid is ____________
a) Removal of the Virulence region
b) Removal of the 25 base pair repeats
c) Removal of the T-DNA
d) Removal of the Host specificity region
Explanation: Disarming of Ti plasmid is done by the removal of the T-DNA. As T-DNA contains genes for cancer it is important to remove that part so that cancer does not occur in the transformed cell. And the gene of interest is placed within the 25 base pair repeats in place of the T-DNA to ensure correct transfer and integration of the DNA insert.
5. Insertion of the T-DNA into the host genome depends on the T-DNA itself.
Explanation: The T-DNA contains the genes to cause cancer and does not play any role in the incorporation of itself in the host genome. The 25 base pair repeats flanking on either sides of the T-DNA is responsible for the incorporation of the T-DNA into the host genome.
6. The Ti cloning vector pBIN19 contains which of the following genes?
a) Tetracycline resistant gene
b) Stress resistant gene
c) Kanamycin resistant gene
d) Ampicillin resistant gene
Explanation: The Ti cloning vector pBIN19 contains kanamycin resistant gene and a lac Z gene. These are incorporated within the 25 base pair repeats and contain a number of cloning sites. These are used for the transformant screening purposes.
7. Transformants of pBIN19 are selected by growing them in solid agar media with ampicillin.
Explanation: Transformants of pBIN19 are selected by growing them in solid agar media with kanamycin. This is because Ti cloning vector pBIN19 contains kanamycin resistant gene and a lac Z gene. If the cells are transformed they will be resistant to the kanamycin present in the culture media.
8. Introduction of new gene through Ti plasmid should be done in ____________
a) Fully grown plant
b) A sapling
c) Germ cells
Explanation: Introduction of new gene through the Ti plasmid should be done in a way that every cell of the plant is transformed. The simplest solution is to infect not the mature plant but the culture of plant cells, callus, or protoplasm in a liquid medium.
9. How the host specificity is achieved by the specificity gene of the Ti plasmid?
a) Opine released by a wounded plant
b) Acetosringone released by bacteria
c) Acetosringone released by wounded part of the plant
d) Opine released by bacteria
Explanation: Acetosringone is released by wounded part of the plant. This chemical is identified by the host specificity gene of the bacteria A. tumefaciens which then infects the plant through the wounded area.
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