Figure 1.

Mitochondrial electron transport chain. The electron transport chain (ETC) is located in the mitochondrial inner membrane. Electrons (dashed lines) from reducing equivalents (e.g., NADH) enter the ETC at complex I (CxI) or complex II (CxII) and reduce the ubiquinone pool (Q, yellow). Electrons are then transferred from QH₂ to complex III (CxIII), to cytochrome c (Cyt c) and ultimately onto oxygen (O₂) at complex IV (CxIV). During this process protons are pumped (not shown) to generate a protonmotive force (Δp) which is comprised of a membrane potential and a proton concentration gradient.