What technique is used for separating nucleic acids or proteins based on their size and charge?

Gel electrophoresis is the correct technique used for separating nucleic acids or proteins based on their size and charge. This process utilizes an electric field to move molecules through a gel matrix, which typically consists of agarose or polyacrylamide. The gel acts as a sieve, allowing smaller molecules to move through more easily while impeding the movement of larger molecules.

As the electric current is applied, negatively charged nucleic acids and proteins migrate toward the positive electrode, and the differential movement based on size and charge allows for their separation. This technique is fundamental in many molecular biology applications, such as DNA analysis, RNA separation, and protein characterization.

Other methods listed, like polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay, serve different purposes. PCR is focused on amplifying specific nucleic acid sequences, Western blotting detects specific proteins using antibodies, and ELISA is used for quantifying antigens or antibodies in a sample. These processes may use gel electrophoresis as part of their methodology, but they do not specifically involve separation based on size and charge in the same direct manner as gel electrophoresis does.