MCQs on Transformation and Hosts
1 - Question
How will we choose which transformation method is to be used?
a) It depends on the available conditions for the reaction to take place
b) It depends on the efficiency which is required to be obtained
c) All the transformation methods can be used equivalently
d) Each reaction has been assigned a particular transformation method
Explanation: The choice of transformation method to be used is based upon the efficiency which is desired in the reaction which has to take place.
2 - Question
The cell in which the recombinant molecules are propagated is termed as __________
Explanation: Hosts are the cells which are used for propagation of recombinant molecules. The choice of a correct host is very important.
3 - Question
Some mutations are present which assist the uptake of DNA. Which of the statement is incorrect for it?
a) deoR is such a mutation which assists the uptake of DNA
b) It is a transcriptional regulator
c) It is having DNA binding activity
d) It controls the expression of a set of genes involved ribonucleoside catabolism
Explanation: There are various factors which affect the uptake of DNA by the cells. deoR is an example of such a mutation which assists the uptake of DNA. It is a transcriptional regulator and is having DNA binding activity. It controls the expression of a set of genes involved in deoxyribonucleoside catabolism.
4 - Question
Endogenous DNA-degrading system is not essential in determining transformation efficiency.
Explanation: Endogenous DNA-degrading system is essential in determining the transformation efficiency.
5 - Question
Which of the following is true for K strain for E. coli?
a) It contains restriction-modification system which is encoded by hsDMRS locus
b) hsDR encodes for endonuclease which is responsible for cleaving the DNA sequence containing –AACGCNNTGC-
c) Cleavage is carried out when the second A is non methylated
d) hsDR mutation can be used for cleavage of incoming unprotected DNA
Explanation: It consists of K restriction-modification system which is encoded by hsDMRS locus. hsDR encodes for endonuclease which is responsible for cleaving the DNA sequencing containing –AACNNNNNNGTGC-. Cleavage takes place only in the case when the second A and the A opposite to T in the second strand is methylated. This mutation can be used to avoid cleavage of incoming unprotected DNA.
6 - Question
Methylation dependent restriction system (MDRS) are included in which class of restriction enzymes?
a) Type I
b) Type II
c) Type III
d) They are the product of mcrA, mcrB or mrr loci
Explanation: MDRS don’t come under the general classification of type I-III. They are the product of mcrA, mcrB and mrr loci. It would degrade DNA containing methylcytosine (mcrA, mcrB) or methyladenine (mrr).
7 - Question
Choose the incorrect statement with respect to dam and dcm genes?
a) Their enzymes are responsible for methylation of DNA
b) Dam protein methylates cytosine in –GATC-
c) Dcm methylates cytosine in-CCAGG- and –CCTGG- sequences
d) The extent of methylation also has effects on the efficiency with which the other restriction enzymes cleave the DNA in vitro
Explanation: The enzymes of dam and dcm genes are responsible for mrthylation of DNA. Dam protein methylates adenine in –GATC- and dcm methylates cytosine in –CCAGG- and –CCTGG- sequences. The extent of methylation also has effects on the efficiency with which the other restriction enzymes cleave DNA in vitro.
8 - Question
How many recombination systems are present in E. coli?
Explanation: There are mainly three recombination systems in E.coli. They are the products of recBCD, recE and recF genes.
9 - Question
Disablement is also done in plasmids. Choose the correct statement.
a) The strains carrying out the recombinant plasmids should not escape outside
b) Preferred strains are having mutations which allow their growth in wild
c) Mutations confer prototrophy
d) If the recombinants escape outside, there is no such harm
Explanation: Disablement is also done in plasmids, in order to ensure that the recombinant plasmids don’t escape outside. If they escape outside, it causes contamination. Preferred strains are having mutations which don’t allow their growth in the wild. Mutations confer autotrophy. Autotrophy is the condition of the introduction of particular metabolites in the medium because they are not synthesized. The opposite of autotrophy is called as prototrophy.
10 - Question
endA mutation is often induced in host molecules. Choose the correct statement.
a) It activates the gene for DNA-specific endonuclease
b) It enhances the yield of plasmid DNA preparations only
c) It enhances the quality of plasmid DNA preparations only
d) It enhances both the quality and yield of plasmid DNA preparations
Explanation: endA mutation is often induced in host molecules. It inactivates the gene for DNA-specific endonuclease. It enhances both the yield and quality of plasmid DNA.
11 - Question
lacZΔM15 represents __________
a) fully present lacZ gene
b) it is not required in alpha complementation
c) it represents the lacZ gene with M15 mutation
d) it is partially deleted lacZ gene which is needed for alpha complementation
Explanation: The representation is for a partially deleted lacZ gene and it is very important for alpha complementation.
12 - Question
The correct statement with respect to lacIq is __________
a) It is a mutant of lac repressor gene and decreases the level of repressor
b) It doesn’t control the lacZ gene
c) It is important for the vectors to replicate in a low copy number
d) It doesn’t titrate out the repressor produced by wild type Lac-I gene
Explanation: It is a mutant of lac repressor gene and decreases the level of repressor. It controls the lacZ gene and it is important for the vectors to replicate with a high copy number. It titrates out the repressor produced by wild-type lac-I gene.