In the context of electrophoresis, what is 'gel' primarily made of?

In electrophoresis, the gel used as a medium for separation is primarily made of agarose or polyacrylamide. These substances are synthetic polymers that provide a stable matrix for the migration of nucleic acids or proteins when an electric current is applied.

Agarose is commonly used for separating larger DNA fragments due to its relatively low resolution compared to polyacrylamide, which is more suitable for resolving smaller fragments or proteins. The size and concentration of the gel can greatly influence the resolution of the separation process, allowing researchers to separate molecules based on size, charge, and shape.

The other options listed do not serve as a gel medium in electrophoresis. Cellulose, while used in some forms of chromatography, does not provide the structural properties needed for gel electrophoresis. Sodium chloride and acetic acid are generally used in buffers or as part of the running conditions in electrophoresis, but they do not constitute the gel itself.