Now, bacteria, doptopsin is a transmembrane into a protein, and that means it spans the entire membrane. And these transmembrane proteins are found in special types of archaeal bacterial cells. Now, the function of this protein is to basically use the energy that is stored in light to basically create a proton gradient. So it moves protons from the inside to the outside of that cell. And by creating this proton gradient, what it does is it synthesizes, it is able to synthesize high energy ATP molecules. Now, if we examine the structure of this transmembrane protein, we'll see it consists of membrane spanning alpha helices.