The cytochrome bc1 complex is a crucial protein complex found in the inner mitochondrial membrane of eukaryotic cells. It plays a key role in the process of cellular respiration, specifically in the electron transport chain, where it helps transfer electrons from ubiquinone to cytochrome c. This transfer is essential for the production of adenosine triphosphate (ATP), the energy currency of the cell. Additionally, the cytochrome bc1 complex contributes to the generation of a proton gradient across the mitochondrial membrane. This gradient is vital for ATP synthesis, as it drives the enzyme ATP synthase to produce ATP from adenosine diphosphate (ADP) and inorganic phosphate. Overall, the cytochrome bc1 complex is integral to energy production in aerobic organisms.