NADH-Coenzyme Q oxidoreductase (Complex I)The first protein complex in the electron transport chain is named NADH-Coenzyme Q oxidoreductase and is commonly labeled Complex I. It is also called NADH dehydrogenase. It is a large L-shaped multiunit protein complex which accepts the high energy electrons from NADH. The NADH molecule donates two electrons to an acceptor group flavin mononucleotide (FMN) which is found on the vertical arm of the complex as shown below. The FMN is reduced to the form FMNH2. From this point the electrons move along a series of iron-sulfur groups (about eight of them) and are transferred to the associated coenzyme Q (ubiquinone). The ubiquinone also extracts two protons from the matrix to form the fully reduced ubiquinol (QH2). As the electrons are moving through the series of FeS clusters, they use the provided electrical energy to pump 4 H+ ions out of the mitochondrial matrix and into the intermembrane space to provide them for the production of the high energy molecule ATP in the oxidative phosphorylation process.
|
Index Photosynthesis Concepts Reference Moore, et al. Ch 7 Ahern Biochemistry.., Ch14 Karp Ch 5.3 AK Lectures Complex I & II | ||
|
Go Back |
Flavin Mononucleotide (FMN)
|
Index Photosynthesis Concepts Reference Moore, et al. Ch 7 Ahern Biochemistry.., Ch14 Karp Ch 5.3 FMN wiki | ||
|
Go Back |
Iron-Sulfur ClustersIron-sulfur proteins play a part in oxidation-reduction reactions in the electron transport chain in mitochondria and chloroplasts. Both Complex I and Complex II have multiple Fe-S clusters for electron transport. |
Index Photosynthesis Concepts Reference Moore, et al. Ch 7 Ahern Biochemistry.., Ch14 Karp Ch 5.3 Iron-sulfur protein wiki | ||
|
Go Back |
Coenzyme Q (Ubiquinone)
The ubiquinol form QH2 is a two-electron carrier, but part of its role in Complex III is to transfer electrons to cytochrome c, which can only accept one electron. This difficulty is overcome partly with the use of the fact that coenzyme Q can also take the form ubisemiquinone with the capacity to transfer just one electron. This is central to its role in the electron transport through iron-sulfur complexes which can accept only one electron. Another useful biological function of coenzyme Q is it's capacity to act as an antioxidant by scavenging free radicals. |
Index Photosynthesis Concepts Reference Moore, et al. Ch 7 Ahern Biochemistry.., Ch14 Karp Ch 5.3 Coenzyme Q wiki | ||
|
Go Back |