The Ubiquinone also uptakes two protons and that helps us establish that electrochemical gradient. And those two H ions bind onto Q to basically form the reduced form of Ubiquinone known as Ubiquinol. And as these electrons move along this proton complex it pumps four H plus ions from the matrix side onto the intermemmbrane side. Now let's move on to complex two. Now, complex two is actually not a proton pump. So that's the main difference between complex one, three and four.