Slide 1 The electron transport chain is composed of proteins that are located in the inner membrane of the mitochondrion (remember, the Krebs cycle occurs in the inner matrix of the mitochondria so the krebs cycle is located close to the electron transport chain). Each successive membrane protein in the electron transport chain has a greater electronegativity (affinity for electrons) than the protein preceding it. NADH and FADH2 deliver electrons to the first protein in the chain. The electrons are passed through the chain due to the increasing electronegativity of each member of the chain until they are stripped away from the chain by oxygen. Water is produced as a waste product when oxygen is reduced. A great deal of energy is released as electrons move from NADH or FADH2 to oxygen. This energy will be used to generate more ATP.
Slide 2 Mitochondria are the powerhouses of the cell. This is because most of the energy that is gained from a glucose molecule is harvested during the Krebs cycle and electron transport - both of which are housed in the mitochondria. The mitochondria are double-membrane bound organelles - there is a smooth outer membrane and highly folded inner membrane. The Krebs cycle is located in the inner space of the mitochondria known as the matrix. The electron transport chain is embedded in the inner membrane. Inside a single mitochondrion there are many Krebs cycles and many electron transport chains - this allows each cell to make a great deal of ATP.
Slide 3 To get an idea of our ATP needs we can look at these calculations. An adult woman needs to burn about 1600 kcal of fuel each day, and our body's fuel is ATP. Each mole of ATP releases about 8 kcal of energy and we can assume that we MAKE just enough ATP to get by in a day. So, doing the math we get: 1600 kcal/day/8 kcal/mol= 200 mol ATP/day. Then we can convert from moles of ATP per day to molecules of ATP/second: 200 mol/day/86400 sec/day= 2.3 x 10^-3 mol ATP /sec Then converting from moles to molecules: 2.3 x 10^-3 mol/sec x 6.02 x 10^23 molecules/mol= 1.4 x 10^21 molecules/sec. With approximately 10^14 cells in the human body, the rate would come to about 107 (10 million) ATP molecules/sec per cell.
Slide 4 This image from the tutorial shows the electron transport chain (in orange) embedded in the inner mitochondrial membrane. It is located next to an enzyme known as ATP synthase - this is the enzyme that will produce the ATP. This is a very important diagram and you should understand it fully to understand the final stages of cellular respiration. To discuss this stage - we will limit our discussion to the delivery of electrons by an NADH molecule and we will ignore FADH2. An NADH molecule with its full load of electrons travels to the electron transport chain and delivers it load of electrons. This regenerates the cell's supply of NAD+ - remember both gylcolysis and the Krebs cycle need a steady supply of NAD+ so this is very important. The NAD+ that is regenerated can now travel back to glycolyis and the krebs cycle so they can continue to run.
Slide 5 The electrons that were delivered by the NADH molecule are at a high free energy state - which means they are unstable and likely to participate in further redox reactions. Each molecule in the electron transport chain is increasingly electronegative so the electrons are pulled through the chain of molecules until they get stripped away from the chain by oxygen (which gets reduced to water). This movement of electrons from NADH to oxygen releases energy that the mitochondrion uses to pump hydrogen ions (or you can call them protons) across the inner mitochondrial membrane from the matrix to the inner membrane space. This can be difficult to understand so please spend time looking at this diagram and fully understanding the details. I have also posted some animations on ANGEL that can help you visualize this process. This movement of hydrogen ions across the inner mitochondrial membrane produces a voltage - in essence - the mitochondrion is like a battery. All of the hydrogen ions trapped in the inner membrane space have high free energy.
Slide 6 The enzyme ATP synthase (shown in gray) uses the energy in this voltage to drive the phosphorylation of ADP to ATP. This is known as oxidative phosphorylation or chemiosmosis (as opposed to the substrate level phosphorylation that we learned about in glycolysis and the krebs cycle). The generation of ATP from chemiosmosis is referred to as oxidative phosphorylation because oxygen's oxidative property allows a large amount of free energy to be made available for ATP synthesis.
Slide 7 At this point, we can look at the energy yield of the entire cellular respiration pathway. Glycolysis produces 2 ATP and 2 NADH. The conversion of pyruvate Acetyl CoA produces another 2 NADH. The Krebs cycle (going through 2 turns per glucose molecule) - produces another 2 ATP plus 6 NADH and 2 FADH2. When the NADH and FADH2 travel to the electron transport chain - they generate another 34 molecules of ATP (each NADH provides energy for 3 ATP and each FADH2 provides energy for 2 ATP). So, the overall energy gain for a respiring cell is 38ATP per glucose. This is a theoretical maximum - in reality most cells will produce fewer ATP molecules than this because of conditions both inside and outside of the cell. However, when we compare this to the ATP gain for a fermenting cell - 2 ATP from glycolysis - we see that respiration is a much more efficient process than fermentation.