Polyacrylamide gel electrophoresis (PAGE) is a technique used to separate biological macromolecules like proteins and nucleic acids based on their electrophoretic mobility. The protocol involves denaturing protein samples, preparing a gel, running electrophoresis to separate the proteins by size, and staining the gel to visualize the separated proteins. PAGE has applications like establishing protein size, identifying proteins, determining sample purity, and quantifying proteins.