Figure 1

Quinones can accept 2 protons and 2 electrons giving rise to 9 redox states. This chemical diversity has been exploited in nearly all biological systems. B) Structure of ubiquinone (co-enzyme Q), the most ubiquitous quinone in nature. The long hydrophobic tail allows it to bind to membranes and proteins and the conjugated ring structure stabilizes electrons, making it the ideal electron transfer molecule.