Electron Transport Chain...oxygen required
Goal: to break down NADH and FADH2, pumping H+ into the outer compartment of the mitochondria
Where: inner mitochondrial membrane
Now that most of the potential energy of glucose is stored in the high energy electron carriers NADH and FADH2, how does a cell extract that potential energy to make more ATP? Just as we reduced these electron acceptors to add potential energy, we will oxidize these electron carriers to extract potential energy. There are two requirements to oxidize NADH and FADH2: an electron acceptor and an electron transport chain (ETC). The ETC is also known as Electron Transport Phosphorylation (or chemiosmosis) because it is a model of mitochondrial ATP production that links H+ transport across the inner mitochondrial membrane to ATP synthesis. In this reaction, the ETC creates a gradient which is used to typically produce 32 ATP's. This reaction is also referred to as oxidative phosphorylation.
The role of electron transport chains
The electron transport chain is a series of membrane bound proteins (cytochromes, FMN, and coenzyme Q) that possess cofactors that are easily reduced/oxidized. These proteins undergo a series of redox reactions that passes electrons from one membrane-bound carrier to another and then to a final electron acceptor, in this case oxygen. By passing the electrons stepwise from NADH (and FADH2) to oxygen, the cell limits the loss of energy in the form of heat and stores the energy to drive ATP synthesis.
ATP is generated as H+ moves down its concentration gradient through a special enzyme called ATP synthase. The inner membrane of mitochondria contains the proteins of the electron transport chain, and is the barrier allowing the formation of a H+ gradient for ATP production through ATP synthetase.
The role of the final electron acceptor
NADH and FADH2 "like" electrons. The cell needs to find a way to get these molecules to release the high energy electrons. The cell requires a molecule that "likes" electrons even more than NADH and FADH2. One such molecule is molecular oxygen (O2). Molecular oxygen exerts a greater attraction for electrons than either of those electron carriers. Therefore, the cell will use O2 to remove the high energy electrons and release the potential energy stored in NADH and FADH2. How does a cell accomplish this electron transfer? Through electron transport chains.
The Electron Transport Chain has a potential yield of 30-32 ATP. Why such a potential range value? The potential range exists because often mitochondria don't work up to capacity. There are various reasons for this, including the fact that a certain number of H+ions leak from the intermembrane space back into the mitochondrial matrix.
A schematic overview of the pathways covered to catabolize glucose in the presence of oxygen:
For a quick overview tutorial of the pathways covered so far to catabolize glucose, click on the following link:
Click on the following link for a brief tutorial of the Electron Transport Chain:
Click on the link below to view an animation of the Citric Acid Cycle:
|The image shows an overview of ETC. Place the correct labels representing energy and final by-product.|