Vector Biology Multiple Choice Questions on “Ligation of Vectors”.
1. Which is the final step in the construction of a recombinant molecule?
A. Plasmid isolation
B. Gene amplification
C. Restriction digestion
D. Ligation
Answer: D
Clarification: The final step in the construction of a recombinant DNA molecule is the joining together of vector molecule and the DNA to be cloned, this is known as ligation.
2. Which DNA ligase enzyme is used in genetic engineering?
A. Bacterial ligase
B. T4 ligase
C. Yeast ligase
D. Pseudomonas ligase
Answer: B
Clarification: The ligase enzyme used in genetic engineering is derived from E.coli cells infected with T4 phage, T4 ligase requires ATP to catalyze the ligation reaction.
3. Within the cell, ligase enzyme has the function of repairing any discontinuities that may arise in the double stranded DNA molecule. What are these discontinuities?
A. Absence of nucleotides in 1 strand
B. Missing phosphodiester bond in 1 strand
C. Missing phosphodiester bond in 2 both strands
D. Absence of nucleotides in both strands
Answer: B
Clarification: DNA ligase repairs the missing phosphodiester bonds in one of the strands of the double stranded DNA. The absence of nucleotides is called nick. A discontinuity is a position where phosphodiester bond between adjacent nucleotides is missing.
4. The chemical reaction involved in ligation of two molecules is same as repairing discontinuities.
A. True
B. False
Answer: A
Clarification: The chemical reaction involved in ligation of two molecules is exactly the same as discontinuity repair, except that two phosphodiester bonds must be made, one for each strand.
5. Which of the following will have more efficient ligation?
A. Sticky ends
B. Blunt ends
C. Blunt ends and high concentration of DNA
D. Blunt ends and low concentration of DNA
Answer: A
Clarification: In the case of blunt ends the ligation is less efficient because ligase cannot catch hold of the molecules to be ligated, and has to wait for chance associations to bring the ends together. Whereas in case of sticky ends can base pair with one another forming hydrogen bonds and a relatively stable structure is formed for the ligase enzyme to work on.
6. Which of the following is not a method for putting sticky ends to a blunt ended DNA fragment to be cloned?
A. Homopolymer tailing
B. Adaptors
C. Restriction digestion
D. Linkers
Answer: C
Clarification: Sticky ends are desirable on the DNA molecules to be ligated together in a cloning experiment. One way of doing this is restriction digestion of the vector and gene to be cloned, but when the vector produced by restriction digestion has sticky ends and the DNA fragment produced, does not; other methods for putting sticky ends to the blunt ended molecule are used.
7. What are Linkers?
A. Short synthetic double stranded DNA sequence
B. Short oligonucleotide sequence of host
C. Short oligonucleotide sequence of vector
D. Short synthetic single stranded DNA sequence
Answer: A
Clarification: Linkers are short double-stranded DNA, artificially synthesized of known sequences. These are used for increasing the efficiency of ligation for blunt ended molecules by converting them into sticky-ended.
8. What is the problem associated with the use of linkers for putting sticky ends to a blunt ended molecule?
A. High ambient temperature requirements
B. Possible cleavage of the DNA molecule itself
C. High cost of synthetic linkers
D. Low compatibility of linkers