So we have two types of subunits that make up this core structure. We have the alpha subunit and we have the beta subunits. So we have seven alpha subunits shown here and seven alpha subunits shown here. 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.