Genetic Engineering Multiple Choice Questions on “Categories of Ligation Reaction”.
1. Ligation is defined as ______________
a) Alignment of only double stranded DNA molecules at the ends and the formation of phosphodiester bonds between both the strands
b) Alignment of either of the double or single stranded DNA molecules and formation of glycosidic bonds between both the strands
c) Alignment of either of the double or single stranded DNA molecules and the formation of phosphodiester bonds. The bond can be between either one or both the strands
d) Alignment of single stranded DNA molecules and formation of glycosidic bonds between these strands
Answer: c
Explanation: Ligation is basically the formation of bonds between the ends of two DNA strands. The strands can be single or double. The nature of the bond is phosphodiester, which means that bond is formed between sugar and phosphate. The phosphodiester bond can either be formed between one strand or both the strands.
2. If only one bond is broken in the sugar-phosphate backbone, it is called as ___________
a) gap
b) nick
c) break
d) leakage
Answer: b
Explanation: In the case, if only one bond is broken in the sugar phosphate backbone, it is termed as nick. If a number of nucleotides are missing, it is termed a gap. Nick can be sealed by ligation reactions but gap can’t be sealed by a ligation reaction.
3. How many categories of ligation reaction are there on the basis of ends created?
a) 1
b) 2
c) 3
d) 4
Answer: b
Explanation: There are two categories of ligation reaction and are named as blunt-ended and sticky ended reaction. They are named because of the nature of the ends of the molecules to be ligated.
4. In the case of blunt-end ligation, blunt ends can be generated by ___________
a) simply the action of restriction endonuclease which gives straight ends
b) the polishing of staggered ends
c) both the action of restriction endonuclease which gives straight ends and polishing of staggered ends
d) by the action of restriction endonuclease which gives staggered ends
Answer: c
Explanation: Blunt ends are those which don’t have single stranded ends as overhangs. The ends are double stranded. And these can be generated by polishing the staggered ends or the action of restriction endonuclease which generate straight ends.
5. The ligation reaction is more efficient in which case?
a) Blunt end ligation
b) Sticky end ligation
c) Both have the same efficiency
d) Depends on the reaction conditions
Answer: b
Explanation: Sticky end ligation is generally more efficient than blunt end ligation. It is so because sticky end ligation is carried out because of complementary base pairing.
6. The sticky ends are held together by which type of bonds?
a) Hydrogen bond
b) Covalent bond
c) Ionic bond
d) Van-der-waal forces
Answer: a
Explanation: The sticky ends are held together by the hydrogen bonds. Hydrogen bonds are weak in nature and can easily be broken.
7. Why sticky ended ligations are carried out at temperatures lower than room temperature?
a) It is so because the vibrational and kinetic energy of the molecules at room temperature is lower than that of the energy required to break the bonds holding the ends
b) The energy required to break the bonds holding the ends is very less than that of the kinetic and vibrational energy at room temperature
c) The enzyme carrying out ligation is unstable at low temperature
d) The sticky ends created, don’t just relegate at low temperature