The Sieve: Agarose Gel Electrophoresis Explained

If agarose is a polysaccharide extracted from marine plants, then it is naturally derived from red seaweed or algae.

If the phosphate groups in the DNA backbone are negatively charged, then the molecule will be attracted to the positive pole (anode) when an electric current is applied.

If the agarose forms a web of tangled fibers, then it creates tiny holes. If smaller DNA pieces can slip through these holes more easily than bulky ones, then the matrix functions as a sieve.

If the gel must be a solid but porous slab, then you need the powder, a liquid to dissolve it, heat to melt it, and a mold to shape it as it cools.

If the gel is a dense mesh, then larger molecules will frequently bump into the fibers and slow down. If smaller molecules encounter less resistance, then they will travel faster and farther in the same amount of time.

If you add more agarose powder to the same amount of liquid, then the fibers will be packed more tightly together. If they are packed tighter, then the holes (pores) between them will become smaller, not larger.

If the gel needs holes to hold the liquid DNA, then a physical spacer must be used while the gel is solidifying. If this tool has teeth like a hairbrush, then it is called a comb.

If the experiment involves an electric current, then the liquid must contain ions to carry the charge. If a stable environment is needed for the DNA, then a buffer is required to prevent the water from becoming too acidic or basic.

If the movement is a race through a mesh, then the DNA's size, the density of the mesh, and the duration of the race all dictate the final position of the DNA bands.

If the term "matrix" describes an environment in which something else is embedded or moves, then the solid-yet-porous structure formed by the cooled agarose is the matrix.

If the agarose molecules link together to form a gel as the temperature drops, then the mixture is undergoing the transition of solidification (or polymerization).

If small fragments move too easily through large holes, then the holes must be made smaller to create resistance. If a high-concentration gel has the smallest holes, then it is best for separating small fragments.

If the matrix traps water inside a network of fibers held by non-covalent attractions, then it is a hydrogel. Agarose gels are solid at room temperature and rely on hydrogen bonds to set.

If DNA is negative and is attracted to the positive end, then it must start at the opposite side to have room to move. If it starts at the negative (black) end, then it can migrate toward the positive end across the gel.

If DNA is naturally clear and invisible, then it must be labeled with something that glows under UV light. If this substance binds to the DNA, then it is a fluorescent dye or stain.

If the agarose powder is not fully melted and dissolved, then the gel will have "clumps" and the matrix will not be uniform. If the matrix is uneven, then the DNA will not separate accurately.

If the name describes the process, then agarose is the seaweed sugar, the gel is the medium, and the electric current is what "carries" the DNA through it. Agarose is a carbohydrate, not a protein.

If a forest is thick with trees (agarose fibers), then a large moose (large DNA) will get stuck or slowed down more often than a small rabbit (small DNA). This is a perfect analogy for how the matrix works.

If DNA is measured by the number of linked nucleotides in its sequence, then the standard unit of length is the count of those base pairs.

If there is no matrix to provide resistance, then all DNA molecules will be pulled by the electricity at the same speed regardless of their size. If they move at the same speed, then they will not separate into distinct bands.