1. Topoisomerase is also an enzyme which is used for carrying out ligation. The correct statement for topoisomerase is?
a) They act only on double stranded molecules
b) They alter the degree of supercoiling of DNA molecules
c) They are less effective than conventional DNA ligase
d) There are three types of topoisomerases
Explanation: Topoisomerases alter the degree of supercoiling of both single and double stranded DNA molecules. There are two types of topoisomerases, I and II. I is responsible for altering single stranded molecules and type II for altering double stranded molecules. They are more effective than conventional DNA ligase.
2. Mobile genetic elements can be transferred from one DNA portion to another. The enzyme carrying out this is ____________
a) Ligase
b) Transciptase
c) Transposase
d) Endonuclease
Explanation: Transposase is used for transferring mobile genetic elements from one portion to another. They are useful in inserting origin of replication or anti-biotic resistance genes.
3. Phage based recombination systems are used for ____________
a) cleaving the molecules at specific sites
b) adding the molecules at specific sites
c) breakage and rejoining the molecules at specific sites
d) breakage at random sites
Explanation: Phage based recombination systems are used for breaking and rejoining the molecules at specific sites and not at random sites
4. Bacteriophage lambda is having a phage recombination system. Following are the characteristics of this system ____________
a) It is used for inserting phage genome into the bacterium
b) It is used for inserting bacterial genome into the phage
c) The specific site in bacteria is attB and that in phage is attP
d) The specific sites in both of them are called as attP
Explanation: The phage genome is inserted into the bacterium. The site for insertion at the phage genome is attP and that in the case of a bacterium is attB.
5.Ligation enzymes are used for ligating newly synthesized okazaki fragments. What holds true for okazaki fragments?
a) Okazaki fragments are short fragments of DNA formed on the leading strand
b) Okazaki fragments are large fragments of DNA formed on the lagging strand
c) Okazaki fragments are short fragments of DNA formed on the lagging strand
d) Okazaki fragments are large fragments of DNA formed on the leading strand
Explanation: Okazaki fragments are short DNA fragments on the lagging template strand during replication. They are complementary to the lagging strand.
6. Isolation of genomic DNA follows the same principles as that of obtaining plasmid from E. coli. Which of the following is not included in it?
a) Cell lysis
b) Removal of proteins
c) Removal of chromosomal DNA
d) Dissolving plasmid in water
Explanation: There are some basic steps which are included in obtaining plasmid DNA from E. coli. Firstly, the cell is lysed, further removal of proteins and chromosomal DNA is done. A plasmid is obtained and collected but not in water. Also, further purification is done if necessary.
7. How many methods are there for obtaining the plasmid DNA from the bacteria?
a) 1
b) 2
c) 3
d) 4
Explanation: There are two methods which are used for obtaining the plasmid DNA from the bacteria. They are named as alkaline lysis method and boiling lysis method. They both are having different working principles
8. Cell lysis is carried out by which substance?
a) Lysozyme and detergents
b) Water
c) Sugar solution
d) Suphuric Acid
Explanation: Cell lysis is carried out by adding lysozyme and detergents. The cell wall is made up of N-acetyl glucoasamine and N-acetyl muramic acid and they are having cross links. The agents added to break the cross links present between the molecules of the cell wall
9. Chromosomal or genomic DNA is separated by ____________
a) Sedimentation
b) Dissolution in water
c) Centrifugation
d) Distillation
Explanation: Chromosomal or genomic DNA is comparatively heavier and large in size than that of plasmid DNA. Hence, centrifuging at a high speed leads to settling down of the genomic DNA and thus can be separated easily.
10. Proteins can be removed via treatment by?
a) Phenol and chloroform treatment
b) Treatment with sodium hydroxide
c) Chloroform treatment alone
d) Centrifuging
Explanation: Proteins can be removed via treatment with phenol and chloroform treatment. Chloroform is alone not sufficient. The phenol added helps in the destruction of proteins and chloroform helps in its dissolution under acidic conditions