Which technique is used to separate protein fragments based on size?

polyacrylamide gel electrophoresis

Southern blot

agarose gel electrophoresis

polymerase chain reaction

A. Polyacrylamide gel electrophoresis (PAGE)

Explanation:

Protein fragments of different size can be separated by gel electrophoresis method. Different proteins are made up of different number of amino acids and so the chain length vary i. e. the size of different proteins may vary. Also different proteins may have different charges due to difference in the type of amino acids present in them.

Generally for separating the protein fragments according to their size polyacrylamide gel is used. Foe this proteins are first given the heat treatment and treated with SDS for unfolding the protein. SDS is a detergent that imparts negative charge to protein. During electrophoresis, under the electric field the separation would be only due to size but not charge as all the proteins are treated with SDS and thus have same negative charge. This method is called SDS-PAGE. Under the electric field, small protein fragments will move fast through the pores compared to large fragments leading to their separation.

If two proteins are of same size then to separate them wither agarose gel electrophoresis is used or isoelectric focusing.