1. 1 24.2 Electron Carriers 24.3 Electron Transport Chapter 24 Metabolism and Energy Production

2. 2 Electron Carriers Electron carriers: Accept hydrogen and electrons from the reduced coenzymes NADH and FADH 2. Are oxidized and reduced to provide energy for the synthesis of ATP.

3. 3 Oxidation-Reduction Electron carriers are continuously oxidized and reduced as hydrogen and/or electrons are transferred from one to the next.

4. 4 FMN (Flavin mononucleotide) FMN coenzyme: Contains flavin, ribitol,and a phosphate. Accepts 2H + + 2e - to form reduced coenzyme FMNH 2.

5. 5 Iron-Sulfur (Fe-S) Clusters Fe-S clusters: Are groups of proteins containing iron ions and sulfide. Accept electrons to reduce Fe 3+ to Fe 2+, and lose electrons to re-oxidize Fe 2+ to Fe 3+.

6. 6 Coenzyme Q (Q or CoQ) Coenzyme Q (Q or CoQ) is: A mobile electron carrier derived from quinone. Reduced when the keto groups accept 2H + and 2e -.

7. 7 Cytochromes Cytochromes (cyt) are: Proteins containing heme groups with iron ions. Fe 3+ + 1e - Fe 2+ Abbreviated as cyt a, cyt a 3, cyt b, cyt c, and cyt c 1.

8. 8 The electron carriers in the electron transport system are:  Attached to the inner membrane of the mitochondrion.  Organized into four protein complexes. Complex I NADH dehydrogenase Complex IISuccinate dehydrogenase Complex IIICoQ-Cytochrome c reductase Complex IVCytochrome c Oxidase Electron Transport System

9. 9 Electron Transport Chain

10. 10 At Complex I, hydrogen and electrons are transferred from:  NADH to FMN. FMN + NADH + H + FMNH 2 + NAD +  FMNH 2 to Fe-S clusters and Q, which reduces Q to QH 2 and regenerates FMN. Q + FMNH 2 QH 2 + FMN  Complex I to Complex III by Q (QH 2 ), a mobile carrier. Complex I NADH Dehydrogenase

11. 11 At Complex II, hydrogen and electrons are transferred from:  FADH 2 to Complex II, which is at a lower energy level than Complex I.  FADH 2 to coenzyme Q, which reduces Q and regenerates FAD. Q + FADH 2 QH 2 + FAD  Complex II to Complex III by Q(QH 2 ), a mobile carrier. Complex II Succinate Dehydrogenase

12. 12 At Complex III, electrons are transferred from:  QH 2 to two Cyt b, which reduces Cyt b and regenerates Q. 2Cyt b (Fe 3+ ) + QH 2 2Cyt b (Fe 2+ ) + Q + 2H +  Cyt b to Fe-S clusters and to Cyt c, the second mobile carrier. 2Cyt c (Fe 3+ ) + 2Cyt b (Fe 2+ ) 2Cyt c (Fe 2+ ) + 2Cyt b (Fe 3+ ) Complex III CoQ-Cytochrome c reductase

13. 13 Complex IV Cytochrome c Oxidase At Complex IV, electrons are transferred from:  Cyt c to Cyt a.. 2Cyt a (Fe 3+ ) + 2Cyt c (Fe 2+ ) 2Cyt a (Fe 2+ ) + 2Cyt c (Fe 3+ )  Cyt a to Cyt a 3, which provides the electrons to combine H + and oxygen to form water. 4H + + O 2 + 4e - (from Cyt a 3 ) 2H 2 O