Genetic Engineering Multiple Choice Questions on “Transformation and Hosts”.
1. 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
Answer: b
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. The cell in which the recombinant molecules are propagated is termed as __________
a) host
b) vector
c) plasmid
d) carrier
Answer: a
Explanation: Hosts are the cells which are used for propagation of recombinant molecules. The choice of a correct host is very important.
3. 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
Answer: d
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. Endogenous DNA-degrading system is not essential in determining transformation efficiency.
a) True
b) False
Answer: b
Explanation: Endogenous DNA-degrading system is essential in determining the transformation efficiency.
5. 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
Answer: a
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. 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
Answer: d
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. 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
Answer: b
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. How many recombination systems are present in E. coli?
a) 1
b) 2
c) 3
d) 4
Answer: c
Explanation: There are mainly three recombination systems in E.coli. They are the products of recBCD, recE and recF genes.
9. 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
Answer: a
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. 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
Answer: d
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. 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
Answer: d
Explanation: The representation is for a partially deleted lacZ gene and it is very important for alpha complementation.
12. 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
Answer: a
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.