We have the C subunit and we have the A subunit. Now, we only have a single A subunit. But for the C subunits we have anywhere from ten to 14 C subunits that aggregate together to form something called the C ring. And it's the C ring, as we'll see in just a moment that actually rotates within the ATP synthase and that allows that gamma epsilon stalk to actually rotate and cause the binding change mechanism that we discussed in the previous lecture. So let's focus on the following diagram. So we have the inner membrane of the mitochondria.