Question

The advantage of using agarose gel in separating DNA is that it

• A. provides sieving effect which helps to separate the DNA molecules
• B. creates an electric field to help the migration of DNA molecules
• C. creates a concentration gradient to allow the diffusion of DNA molecules
• D. provides a cool environment to help separate the DNA molecules

Answer 1

The correct option is A provides sieving effect which helps to separate the DNA molecules

Agarose gel is the solidified gel which serves as the matrix with definite pore size in gel electrophoresis. It is obtained by dissolving agarose powder in a buffer followed by cooling the mixture for solidification. Agarose is a polysaccharide composed of repeating units of agarobiose. Agarobiose is composed of two different monomers: D-galactose and 3,6-anhydro-L-galactopyranose. The cross linkage between these monomers creates pores in the agarose gel. The size of the pore depends on the degree of cross-linkage which is determined by the concentration of agarose. The pores present in the agarose gel creates a sieving effect that helps to separate DNA molecules under an electric field. For DNA molecules, those with greater number of base pairs face greater resistance to travel through pores of a given size. Hence, the pores in agarose gel act as a sieve that allow the smaller and compact DNA molecules to pass through them easily.


The power supply connected to the electrodes present in an electrophoresis chamber helps to provide suitable voltage across the cathode (negative terminal) and anode (positive terminal). This creates an electric field which drives migration of DNA molecules.

The agarose gel is of uniform concentration throughout. Hence, no gradient with respect to concentration is created to separate DNA molecules.
Agarose gel does not influence the temperature of the experiment.