1. Oxygen concentrations began to build up in the early atmosphere of the Earth when all the iron was finished turning to rust!

2. The electron transport chain receives the high energy electrons from the TCA (citric acid) cycle and from NADH brought into the mitochondrion from glycolysis. ATP is generated through the chemiosmotic coupling.

• The inner membrane of the mitochondrion is the site for the electron transport chain and the generation of ATP. (fig. 12-6a, Lodish)
• Reduction is the addition of electrons and oxidation is the removal of electrons. Thus, oxidation of NADH to NAD⁺ involves the removal of electrons from NADH. These "high energy" electrons transfer the energy conserved in the processes of glycolysis and the citric acid chain into the electron transport chain.
• Transfer of electrons by NADH results in a H⁺ being pumped across the inner membrane at three sites. (fig. 12-16a, Lodish)
• Transfer of electrons from succinate, an intermediate in the citric acid cycle, also results in a H⁺ being pumped across the inner membrane. (fig. 12-16b, Lodish) Notice how this step involves FAD. Electron transfer from FADH₂ (citric acid cycle and glycerol-phosphate shuttle) enters the electron transfer chain here. (fig. 12-18, Lodish)
• Electron transport involves components such as the cytochromes, "cell colorings". In the following diagram you can see how cytochrome c donates electrons (reducing power) to a pair of copper atoms associated with the cytochrome oxidase complex. Then, the coppers donate electrons to an iron associated with another component of the cytochrome oxidase complex - cytochrome a . Cytochrome a, like hemoglobin, has a bound heme group and an iron atom.
• The last step of the electron transport chain transfers the leftover, low energy electrons to oxygen to form water. This last step is, of course, blocked by a lack of oxygen, all the reactions back up and a person dies. Fermentation in humans only works in muscle and not in other cells so the other cells run out of ATP and everything stops. Rotenone is a type of rat poison which blocks the first step of the electron transport chain. Cyanide (CN^-) acts in a very similar fashion but blocks the transfer of electrons to Oxygen in the very last step of the electron transfer chain.
• Did you know that kangaroo rats can live their entire life without drinking a drop of water? This can happen because these animals live off the water produced by the last step in the electron transport chain. Look here to learn more.
• ADP is phosphorylated to form ATP by chemiosmosis, a process that is common to bacteria, mitochondria, and chloroplasts. (fig. 12-22, Lodish)
• The ATP synthase is a weird protein with a rotor! (fig. 12-24, Lodish) (fig. 12-25, Lodish) We will discuss these two figures from Lodish in some detail. Make sure that you read in Lodish and understand the details in figs. 12-24 and 12-25.
• The ATP synthase is reversible and can run in either direction. (look!)
• An interesting insight into how mitochondria are related to bacteria might be hinted at by this data: The 13 proteins encoded by mitochondrial DNA (human) are the following: 7 subunits of NADH dehydrogenase, 2 subunits of ATP synthase, 3 subunits of cytochrome c oxidase, and cytochrome b. All are components of the mitochondrial inner membrane and none are components of the TCA (citric acid) cycle. Later in the course, we will show how proteins are "translocated" from the cytosol into the matrix of the mitochondrion (and the stroma of the chloroplast). So, apparently, enzymes of the TCA (citric acid) cycle are coded for by nuclear DNA, manufactured in the cytosol, and then translocated across the mitochondrial membranes into the matrix. Proteins like cytochrome and components of the ATP synthase are coded for by the mitochondrial DNA and might have had some function in bacteria before they became endosymbionts of eukaryotic cells.

All text and images, not attributed to others, including course examinations and sample questions, are Copyright, 2006, Thomas J. Herbert and may not be used for any commercial purpose without the express written permission of Thomas J. Herbert.