Figure 1.

ETS. NADH and FADH₂ are derived from the metabolism of substrates such as pyruvate, malate, glutamate, and succinate through the TCA cycle. NADH and FADH₂ deliver electrons to the ETS at CI and CII, respectively. Electrons from CI and CII converge at the Q junction (Q) and are transferred to CIII, then finally to CIV via cyt c. At CIV, oxygen (O₂) and hydrogen ions (H⁺) combine to form water (H₂O), the final electron acceptor. Hydrogen ions are pumped from the mitochondrial matrix to the intermembrane space between the inner and outer mitochondrial membranes, creating a proton gradient across the inner mitochondrial membrane. Hydrogen ions flow back to the mitochondrial matrix along the concentration gradient at CV (ATP synthase), producing ATP. Created with BioRender.com.