So we have four major types of complexes protein complex one, protein complex two, protein complex three, and protein complex four. In addition, additionally also have two very important electron carrier molecules used by the electron transport chain. One of them is known as Q, which stands for Coenzyme Q, also known as Ubiquinone, and the other known as the other one is known as Cytochrome C. So in this lecture, I'd like to briefly discuss these different types of structures. And in the next many lectures to come, we're basically going to look at the details of what actually happens within each one of these complexes. So let's begin with protein Complex to one. Now, by the way, this is a diagram of only one of the electron transport chains of the many electron transport chains that exist in a single mitochondrial inner membrane.