Question: Which of the following is the first complex of the Electron Transport Chain (ETC)?
A Complex II
B Complex IV
C Complex I
D Complex V
Answer: Complex I
| Name of ETC complex | Location in the cell | Function | |
| Complex I | NADH dehydrogenase | Inner mitochondrial membrane
| · Transfers electrons from NADH to ubiquinone (Coenzyme Q). · It also pumps protons (H+) across the membrane to establish the proton gradient. |
| Complex II | Succinate dehydrogenase | · Transfers electrons from succinate to Coenzyme Q. | |
| Complex III | Cytochrome bc1 complex | · Transfers electrons from Coenzyme Q to cytochrome c. | |
| Complex IV | Cytochrome c oxidase | · Facilitates the final transfer of electrons from cytochrome c to molecular oxygen (O2) which results in the production of water (H2O). · It also pumps protons (H+) across the membrane. | |
| Complex V | ATP synthase (F1Fo ATPase) | · Uses the proton gradient established by the other complexes to produce ATP from ADP and Pi. |