Western blot
Sometimes scientists denature the proteins before the Western blot.  Proteins are long chains of amino acids, like beads on a string.  Most of the time, proteins are crumpled or squashed into balls or other shapes.  A large protein in a tight ball will move faster than a large protein unfolded like a string.  This can be confusing.  Denaturing the protein makes it unfold so it is more like a string.  This makes it easier to tell large proteins from small ones.  Scientists put the chemical sodium dodecyl sulfate (SDS) in the gel so the proteins stay unfolded.  Otherwise, the proteins shrink into their tight ball shape again.