Well, the second electron moves onto the heme groups of Cytochrome B before actually being picked up by Ubiquinone. Now, this Ubiquinone is not the same one as this Ubiquinone. So complex four, complex three actually contains an additional Ubiquinone that is attached onto a different site. And this Ubiquinone is actually used to recycle this electron so that once the Ubiquinone picks up that electron, it is partially reduced into semiquinone radical ion, which is given by this designation. So Q a single electron and that negative sign. Now, this is the first half cycle.