MCQs on Cloning using a Simple Plasmid and Alpha Complementation – 2
1 - Question
Which of the following is true regarding taking up of plasmid DNA in the bacterial cells?
a) There are more chances of having two plasmids in a single cellC
b) There are more chances of having a single plasmid in one cell
c) Uptake upto two plasmids is possible but not more than that
d) Both are taken up with the same efficiency
Explanation: There are more chances of having a single plasmid in one cell. But there are possibilities of having two plasmids in a single cell but the chances are less.
2 - Question
If genomic DNA has been inserted instead of the plasmid, what will happen?
a) It would lead to inactivation of lacZ gene
b) The X-gal substrate would be broken down
c) The colonies formed are blue in colour
d) The lacZ gene would be intact
Explanation: If genomic DNA is inserted instead of the plasmid the lacZ gene would be inactivated. The X-gal substrate won’t be broken down and thus the colonies formed would be white or off-white.
3 - Question
Often PCR can be performed in order to confirm whether an insert is present in the plasmid. Cells are taken directly and PCR is performed, this type of PCR is known as __________
a) direct PCR
b) colony PCR
c) quantitative PCR
d) in-situ PCR
Explanation: When cells from colonies are taken and directly PCR is performed, it is called as colony PCR. Primers anneal to each side of the cloning site and there is no need of purification in such cases.
4 - Question
Generation of recombinants by randomly cloning fragments of total DNA from an organism is called as __________
a) genomic library
d) shotgun cloning
Explanation: Generation of recombinants by randomly cloning the fragments of total DNA from an organism is called as shotgun cloning. Collection of such fragments is known as a library.
5 - Question
The phenomenon of alpha complementation is __________
a) α + β = ω
b) α = β + ω
c) β = α + ω
d) It is either α + β = ω or β = α + ω
Explanation: Alpha complementation is the phenomenon of having the alpha and beta subunit combining to give the omega subunit. These are the different genes of the lac operon.
6 - Question
An operon is defined as __________
a) A related set of genes each having different promoters and are present differently
b) A set of genes which are present together but are controlled by different promoters
c) A set of genes which are present together and are controlled by the same promoter
d) A set of genes which are not present together but controlled by the same promoter
Explanation: An operon is defined as the cluster of genes which are present together and are controlled by the same promoter. An example is lac operon. It consists of three subunits, alpha, beta and omega.
7 - Question
Why the whole lacZ gene can’t be present in the plasmid at one time?
a) Because the whole lacZ gene can’t be present anywhere
b) The whole lac Z gene is very large in size and the plasmid size is small
c) The whole lacZ gene is never functional
d) Because the plasmid takes is having a restriction site only for taking up a portion of the lacZ gene
Explanation: The whole lacZ gene is not present in a plasmid because the plasmids are generally small in size and the lacZ gene is large in size. And if the whole gene is present, it makes the overall size very large.
8 - Question
Alpha complementation is an indicator of lacZ system. Which of the statement is incorrect for it?
a) One portion of the lacZ gene known as minigene is present in the plasmid
b) Another portion is present in the host itself
c) If they both are allowed to combine in the presence of IPTG, X-gal and ampicillin, blue colonies are observed
d) If insert is also present along with host and plasmid, it results in the formation of blue colonies
Explanation: Alpha complementation system is used as a lacZ indicator system. In this, one portion of the lacZ gene is present in the plasmid and is termed as minigene. The other portion is present in the host itself. The combining of two portions is very important to have an intact lacZ gene and in the case, it is intact blue colonies are observed in the presence of IPTG, ampicillin and X-gal. It is so because lacZ breaks down X-gal and it gives blue colour. If the insert is also there, the lacZ gene is interrupted and thus X-gal is not broken down and hence white colonies are obtained