1. Bal31 is also an enzyme which is used. Which of the following statements hold true in its context?
a) It is having only 3’-5’ exonuclease activity and no endonuclease activity
b) It is having only an endonuclease activity
c) It is having 5’-3’ exonuclease activity
d) It leads to shortening from both the ends
Explanation: Bal31 is having an exonuclease activity in 3’-5’ direction and also an endonuclease activity. Thus, after having 3’-5’ exonuclease activity, the endonuclease activity takes place and the molecule is shortened from both the ends.
2. The extent of deletions can be manipulated by controlling which of them?
a) Time of incubation only
b) Amount of nuclease added
c) They both have a role to play in the extent of the deletion
d) The amount of deletion which can be carried out for a particular amount of DNA is fixed regardless of the amount of nuclease and incubation time
Explanation: The extent of deletion can be varied by varying the incubation time and the amount of nuclease added. Thus, they both play a role in controlling the extent of deletion.
3. What is the function of methylase?
a) Addition of methyl groups to DNA
b) Removal of methyl groups from DNA
c) Both in removal and addition of methyl groups from DNA
d) It is used in production of methane gas
Explanation: Methylase is used for the addition of methyl groups on DNA. It is done via placing the methyl groups which are taken from S-adenosyl methionine.
4. Methylase is useful in cloning experiments.
a) True
b) False
Explanation: It is useful in cloning experiments because as it methylates DNA, that DNA is protected from that group of restriction enzyme. It means that if we carry out methylation by EcoRI methylase, the DNA won’t be cleaved by the restriction enzyme EcoRI. In cloning experiments, sometimes it is necessary to protect the DNA from cleavage by a particular enzyme.
5. 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
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.
6. If only one bond is broken in the sugar-phosphate backbone, it is called as ___________
a) gap
b) nick
c) break
d) leakage
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.
7. How many categories of ligation reaction are there on the basis of ends created?
a) 1
b) 2
c) 3
d) 4
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.
8. 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
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.
9. 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
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.
10. 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
Explanation: The sticky ends are held together by the hydrogen bonds. Hydrogen bonds are weak in nature and can easily be broken.