Blots in Molecular Biology

Blots in Molecular Biology

Southern Blotting
Southern blotting is a sensitive method for the detection of a DNA sequence within a mixture.
The DNA first is cleaved (cut) with a restriction enzyme to produce fragments that can be separated by electrophoresis.
After electrophoresis, DNA fragments are transferred to a nitrocellulose membrane by capillary action, creating a replica of the original gel.
The membrane is incubated with a labeled probe which binds to and detects the fragment of interest.

Northern Blotting
Northern blotting is a method for the detection of a specific mRNA in a mixture of RNAs.
Like Southern blotting the method is highly specific and sensitive. RNA from a cell/tissue is extracted and separated by electrophoresis.
As in Southern blotting the RNA is transferred to a nitrocellulose membrane and incubated with a labeled probe that is complementary to the RNA.
The method can be use to quantitate transcription of a mRNA under different cellular conditions.

Western Blot
A western blot is a laboratory method used to detect specific protein molecules from among a mixture of proteins.
This mixture can include all of the proteins associated with a particular tissue or cell type.
Western blots can also be used to evaluate the size of a protein of interest, and to measure the amount of protein expression.
This procedure was named for its similarity to the previously invented method known as the Southern blot.

Other Blots
Eastern Blot: used for the detection of specific posttranslational modifications of proteins.

Far-Western Blot: Uses antibodies to detect the presence of the protein–protein complex, making the Far-Western blot a specific case of the Western blot.

Southwestern Blot: based off the Southern blot and is used to identify and characterize DNA-binding proteins by their ability to bind to specific oligonucleotide probes.

Reverse Northern Blot: differs from both northern and Southern blot in that DNA is first immobilized on a blotting matrix and specific sequences are detected with labeled RNA probes.

Dot Blot: is a special case of any of the above blots where the analyte is added directly to the blotting matrix (and appears as a "dot")