And in the middle we have these two ring structures that each consist of seven beta subunits. So we see that we form four of these rings that stack on top of one another and when they stack on top of one another they basically form this hollow cavity and within that hollow cavity is where we have the catalytic activity of this core structure. So we form this barrel core and it's the barrel core that catalyzes the breakdown of protein. Now, what exactly are the function of these 219s subunits? Well, it's the 19s subunits that essentially locates and binds to the polyubiquid native protein and once it locates it it has Atpa's activity that allows the 19s regulatory subunits to actually begin unfolding that protein. Why do we need to unfold the protein?