Mitochondria are the central organelles for the creation of ATP in oxidative metabolism. A mitochondrion can be as small as a few hundred nanometers long, although they are usually more than ten times larger. A few hundred nanometers is a few thousand angstroms. So the mitochondrion would be a few thousand to a few tens of thousands of chemical bonds long. In a few weeks, we are going to be studying oxidative metabolism, and it will really help if you can visualize a mitochondrion in a concrete way down to the molecular level. Picture the plasma membranes of its outer and inner membranes. Picture he cytochrome system on the inner membrane. Picture the contents of the matrix (water, ATP, NADH, the intermediates of the citric acid cycle). Picture the proton gradient between the inner and outer compartment. Strive for a picture of the biological molecules within the aqueous solution environment as a very complex system of electric charges with chemical structure. Imagine step by step, pulling the atoms apart of the molecules of glycolysis or the citric acid cycle and letting them fall together into the next forms in the pathways. What is happening to energy? Imagine chemiosmosis across the inner membrane as if you were watching water fall through the hydroelectric power station, but instead of gravitational potential energy doing the work of pumping protons, in the mitochondrion, the potential energy decrease is electrostatic. The key to chemiosmosis is oxygen down at the end of the electron transport chain, electron greedy, with its thin electron cloud barely shielding its powerful nucleus, pulling the electrons towards itself, driving the proton pumps.

We are getting close to oxidative metabolism in this course! Not long now.