Question

How proton gradient is established?

Answer 1

There are four protein complexes in the ETS. Complex I involves in pumping H${}^{+}$ ions from the matrix into the intermembrane space. Complex II receives FADH${}_2$ and delivers electrons to ETS. Ubiquinone accepts these electrons and passes them to cytochrome c (complex III) to transport to complex IV. Complex IV reduces oxygen and receives 2 H${}^{+}$ from surrounding to make water. This movement of electrons results in the establishment of the proton gradient. ETS pumps the H${}^{+}$ from the matrix to the intermembrane space. Hence, there are more protons outside than inside.