This set of Molecular Biology Multiple Choice Questions & Answers (MCQs) focuses on “Manipulating DNA”.
1. During DNA cloning which of the following is not a crucial requirement?
a) DNA inserts
b) Vector
c) Protein expression
d) Molecular cutter
View Answer
Explanation: DNA cloning typically involves a vector that carried the DNA insert into a host cell. Molecular cutters are important to incorporate the DNA insert into the vector thus giving rise to the chimera molecule. Hence cloning is complete if the organism replicates and the DNA insert replicates along with it.
2. Transformation does not involve ____________
a) Cutting
b) Recombination
c) Propagation
d) Expression
View Answer
Explanation: Transformation specifically involves the cutting of vector and gene of interest with specific cutters. These are then ligated and thus formed molecule is is the recombinant molecule. This molecule is then propagated into the host cell thereby ending the process of transformation of the host.
3. Which is the most common organism considered for genetic manipulations?
a) E. coli
b) Saccharomyces cerevisiae
c) Cyanobacteria
d) Bacillus Subtilis
View Answer
Explanation: The DNA fragment to be cloned needs to be inserted within the vector to be replicated within the host. By far the most common host used to propagate DNA and thus genetic manipulations is E. coli.
4. Which of the following is an essential feature for being a perfect vector?
a) Origin of replication
b) Selectable marker
c) Restriction site
d) Virulent gene
View Answer
Explanation: A vector typically has three characteristics:
i. It must contain an origin of replication.
ii. It must contain a selectable marker.
iii. It must have one or more restriction sites for restriction endonucleases.
5. DNA ligase can ligate restriction site ends produced by EcoRI to the ends of DNA insert cut by the same enzyme.
a) True
b) False
View Answer
Explanation: EcoRI generates protruding 5’ ends (sticky ends) that are complementary to each other. Thus the ends are capable of reannealing with each other. Thus when both vector the same enzyme and DNA insert are cut using same cutter the strands anneal themselves but leaves two nicks in both the strands. Thus treatment with the enzyme ligase seals the nicks using ATP.
6. The vector and the DNA insert are cut by different enzymes for convenience.
a) True
b) False
View Answer
Explanation: A target DNA is cleaved with a restriction enzyme to generate potential DNA inserts with sticky ends. Vector DNA that has been cut with the same enzyme produces compatible over hangings thus making it convenient for the purpose of annealing and ligation.
7. What is the major difference between cloning vectors and primary vectors?
a) Selectable marker
b) DNA inserts
c) Presence of promoter
d) Presence of two Ori
View Answer
Explanation: The major difference is the presence of suitable promoter before the DNA insert. In case of an expression vector the main motto is the production of protein thus a promoter in essential criteria but in case of the cloning vector it is mainly used for amplification and/or production of library.
8. Which of the following is the primary use of an expression vector?
a) DNA library
b) DNA purification
c) Protein production
d) DNA cloning
View Answer
Explanation: An expression vector is the type of vector that is designed for the expression of genes in cells. the can produce a large amount of proteins particularly useful if the gene product is toxic or a subunit vaccine.
9. Under the influence of which ion does E. coli takes up plasmid from the environment?
a) Nickel
b) Copper
c) Lead
d) Sulphur
View Answer
Explanation: The presence of copper (Cu2+) makes the cell wall of E. coli porous. This facilitates the uptake of external plasmid DNA by applying little agitation.
10. The process by which every type of transformant can be identified is __________
a) Replica plating
b) Hybridization
c) Blotting
d) Insertional inactivation
View Answer
Explanation: Insertional inactivation is the process by which a marker gene is inactivated by inserting the DNA insert within that gene. This leads to visual identification if the gene inactivated gives a coloured product when grown in suitable medium. Also, the marker inactivated may be an antibiotic resistant gene where the cells are grown in suitable antibiotics following the process of replica plating.
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