Question

What is the first step in Southern blot technique ?
A) Denaturation of DNA on the gel for hybridization with specific probe
B) Production of a group of genetically identical cells
C) Digestion of DNA by restriction enzyme
D) Isolation of DNA from a nucleated cell such as one from the scene of crime

Answer 1

A Southern blot is a method used in molecular biology for the detection of a specific DNA sequence in DNA sample. The method of Southern blotting is named after the British biologist Edwin Southern who first published it in 1975.

Complete answer:

First step is isolation of DNA from a nucleated cell such as from the crime scene.
Restriction endonucleases are then used to cut high molecular weight DNA strands into smaller fragments.
The DNA fragments are then electrophoresed on agarose gel to separate them by size.
The method known as alkaline transformer is used.
Then depending on the direction of the transfer the gel, a sheet of nitrocellulose or alternatively nylon membrane is placed on the top of or below
In order to permanently attach the transferred DNA to the membrane, the membrane is then exposed to Ultraviolet radiation.
The membrane is then uncovered to a hybridization probe, a single DNA fragment with a specific sequence and the presence of which in the target DNA is to be determined.
After hybridization is complete, excess probes are washed from the membrane. The pattern of hybridization is later visualised on X-Ray film by autoradiography.

Hence the correct answer is option( D ).

Note: Protein detection is done by Western blotting.

RNA detection is done by using the technique known as Northern blotting.
Southern blotting which is used to detect DNA. Is one of the important processes as it is used in forensic.