Answer:
Three proteins directly contribute to the proton gradient by moving protons across the membrane
Explanation:
The Electron transport chain is a group of proteins and molecules incrusted in the internal mitochondrial membrane and organized into four complexes, I, II, III, and IV. These complexes contain the electron transporters and the enzymes necessary to catalyze the electron transference from one complex to the other. Complex I contains the flavine mononucleotide -FMN- that receives electrons from the NADH. The coenzyme Q, located in the lipidic interior of the membrane, conducts electrons from complex I and II to complex III. The complex III contains cytochrome b, from where electrons go to cytochrome c, which is a peripheric membrane protein. Electrons travel from cytochrome c to cytochromes a and a3, located in the complex IV. Finally, they go back to the matrix, where they combine to H+ ions and oxygen, to form the water molecule. As electrons are transported through the chain, protons are bombed through three proteinic complexes from the matrix to the intermembrane space. These are complexes I, III and IV.
