Question

Match the entries in column I with those of column II and choose the correct option

	Column I		Column II
A	Denaturation	M	Separation of DNA fragments on gel slab
B	Southern blotting	N	Converts DNA into single-stranded molecule
C	Electrophoresis	O	DNA transferred to nitrocellulose sheet
D	PCR	P	X-ray photography
E	Autoradiography	Q	Produces DNA fragments of different sizes
F	DNA treated with restriction endonuclease	R	DNA amplification

• A. A - N, B- Q, C- P, D- R, E- M, F - O
• B. A - P, B - R, C - M, D -O, E - N, F - Q
• C. A - Q, B - O, C - M, D - R, E - P, F - N
• D. A - N, B - O, C - M, D - R, E - P, F - Q

Answer 1

The correct option is D A - N, B - O, C - M, D - R, E - P, F - Q

PCR or Polymerase Chain Reaction is a technique used in molecular biology to create several copies of a certain DNA segment, using thermostable DNA polymerase (Taq DNA polymerase). Hence, amplification of DNA can be achieved by using PCR technique.

The steps involved in this process are denaturation, annealing and extension.

Denaturation occurs when the reaction mixture containing DNA is heated to 96℃. This breaks the hydrogen bonds between the two strands of DNA and converts it into a single-stranded DNA.
The single strands now act as a template for the production of new strands of DNA.

In Southern blotting, the fragments of DNA are separated by gel electrophoresis on the basis of their size.

Later they are transferred to the nitrocellulose membrane where a probe which is radiolabeled and complementary to the specific DNA sequence hybridises. Using X-ray they can be detected on the photographic film. This technique is called autoradiography.

Electrophoresis is a technique used to separate macromolecules in a fluid or gel based on their charge and size under an electric field. Charged macromolecules are placed in the electric field and move towards the negative or positive pole based on their charge. DNA has a negative charge and therefore it migrates towards the anode. The fragments with smaller size move faster in comparison to the fragments with larger size and hence smaller fragments reach near about the end of the gel whereas larger fragments stop early.

A restriction enzyme or restriction endonuclease cuts the DNA double helix at a specific site known as the recognition sequence. Eg: EcoR I is a restriction enzyme isolated from E.coli.