In agarose gel electrophoresis, which property of the molecules affects their movement through the gel?

In agarose gel electrophoresis, the movement of molecules through the gel is primarily influenced by their electric charge. When an electric field is applied across the gel, charged molecules, such as DNA, RNA, or proteins, will migrate towards the electrode with the opposite charge. The degree and direction of their movement depend on the strength of the electric charge they carry.

Molecules with a higher charge density will generally move faster through the gel than those with a lower charge, allowing for the separation of different species based on their net charge. This is fundamental in techniques like DNA analysis, where negatively charged DNA fragments migrate towards the positive electrode, enabling their separation based on size and charge from one another as they travel through the porous matrix of the gel.

While atomic weight, molecular volume, and polymer length can influence the overall behavior of molecules, it is the electric charge that directly governs their movement under an electric field. Larger molecules might move more slowly due to increased resistance from the gel matrix, but without the component of charge, they would not move through the gel at all. Thus, the key property affecting their movement in this specific context is the electric charge of the molecules.