Agarose is a polysaccharide that is isolated and purified from agar or agar-bearing marine algae (sea kelp). It is a natural polymer, made up of alternating β-D-galactose and 3,6-anhydro-L-galactose units of agarobiose in its chemical structure. The linear agarose polymer forms chains which create fibers that are flexible and form a web of channels with diameters from 50 nm to 200 nm, depending on the amount of agarose used.
Agarose is used in gel electrophoresis. When the agarose is heated in a buffer (water with some salts in it) and allowed to cool, it will form a solid, slightly squishy gel. At the molecular level, the gel is a matrix of agarose molecules that are held together by hydrogen bonds and form tiny pores.