MCQs on Screening by Expression In Vivo
1 - Question
At times screening is done for the protein product of DNA of interest rather than the sequence itself. How many methods are there to carry out this?
Explanation: The two methods for this procedure are the direct selection for insert function and the second is ligand binding by the expressed protein.
2 - Question
Choose the correct statement if the screening is carried out by screening by expression in vivo.
a) The proportion of recombinants carrying gene of interest is small
b) The recombinants carrying gene of interest don’t complement the host mutation
c) Mutation should be affecting many genes
d) Most of the products selected would be result of complementation
Explanation: The proportion of recombinants carrying the gene of interest is small. The host is mutant towards the gene of interest and thus the recombinants complement the host mutation. Mutation used should affect only one gene. The most of the products selected would be a result of reversion of only mutation and not complementation.
3 - Question
Choose the incorrect statement with respect to host used.
a) The host must carry mutation for the gene of interest
b) The host should not contain restriction enzymes
c) The host if having restriction enzymes, then the incoming DNA should not be methylated
d) The host should be deficient in recombination
Explanation: The host used must carry the mutation for the gene of interest. The host must not contain restriction enzymes. If the host is having restriction enzymes then the incoming DNA must be methylated. If the incoming DNA is not methylated, then it would be cleaved by restriction enzymes. The host should also be deficient in recombination otherwise it would be difficult to get it.
4 - Question
If the gene to be screened belongs to prokaryotic species then there are chances that it is not expressed.
Explanation: In the case, if gene which is to be screened belongs to prokaryotic species than there are chances that it is not expressed. There are chances that promoter is not present in the insert region.
5 - Question
If the library to be screened and the host belongs to different species, then it is called as ___________
a) homologous selection
b) heterologous selection
c) intraspecies selection
d) mixed selection
Explanation: If the library to be screened and the host belong to different species, then it is called as heterologous selection. In this case, there are chances that protein is expressed but it is non functional.
6 - Question
The direct selection allows _______ number of recombinants to be screened and _______
a) less, slowly
b) less, quickly
c) more, quickly
d) more, slowly
Explanation: If the direct selection is carried out on a plate, then the process results in the screening of more recombinants and it is done quickly and easily.
7 - Question
Xenopus oocyte cells are also used at the time to carry out screening. Choose the incorrect statement for this procedure.
a) DNA from collections is transcribed within in vitro and the transcription products are microinjected into oocytes
b) The RNA is translated within oocytes
c) Screening is carried out on the basis of DNA
d) The screening is helpful for the proteins whose function can be easily screened such as transport of ions
Explanation: DNA from collections is transcribed within in vitro and the transcription products are microinjected into the oocytes. The RNA is translated within the oocytes and screening is carried out on the basis of RNA. The screening is helpful for those proteins whose functions can be easily screened such as transport of ions.
8 - Question
In the case of ligand binding by the expressed protein, the library can be screened by ______________
a) immunochemically, by the use of antibodies
b) ligands if the sequence we are looking for encodes a protein specific to a ligand
c) using a specific DNA sequence which can bind to the protein encoded by the sequence of interest
d) all of the mentioned
Explanation: There are various ways to screen such a library. It can be done immunochemically i.e. by the use of antibodies. Ligands can also be used which bind to the specific proteins encoded by the sequence. There are also cases in which specific DNA sequences bind to the protein encoded by the sequence of interest.
9 - Question
In the case of immunochemical screening, the position of ________ antibody is detected by ________ antibody.
a) secondary, primary
b) primary, secondary
c) primary, tertiary
d) secondary, tertiary
Explanation: In the case of immunochemical screening, the position of the primary antibody is detected with a secondary antibody. Secondary antibody is common for all the primary antibodies and thus detection becomes easier.
10 - Question
The ligand should bind to a single protein only for the screening process.
Explanation: The ligand should bind to a single protein only for the screening process, because if binds to a heterodimer than both the proteins should be present and then it would become difficult.
11 - Question
Choose the incorrect statement for panning.
a) It is a variant of ligand binding approach
b) The ligand is immobilized on the solid support and the cells are passed over it
c) If the ligand-binding domain is exposed on surface of the any recombinant molecules then they will bind to ligand
d) They are not useful for scanning libraries in cultured mammalian cells
Explanation: Panning is a variant of ligand binding approach. In this, the ligand is immobilized on the solid support and the cells are passed over. If the ligand binding domain is exposed on the cells they would bind to the ligand and would be recovered afterward. They are useful in screening libraries in cultured mammalian cells because the cell wall is not there and thus access is easy.
12 - Question
If screening is carried out by using a combination of nascent peptide and mRNA, then it is called as ________
a) nascent peptide display
b) mRNA display
c) ribosome display
d) ribozyme display
Explanation: In the case of ribosome display, a pool of translating ribosomes is used. In this, nascent peptide and mRNA is there. It is passed over solid support which is having ligand attached to it. Ribosomes which encode a protein that binds to the ligand are attached.