We instead use our proton pumps, so we allow the flow of hydrogen ions down the electrochemical gradient. Now, the structure of eukaryotic flagella is much more complicated than our prokaryotic flagella. For the eukaryotic case, we have a nine plus two arrangement of microtubules. In this case, we simply have our single protein, the Flagellum, that wraps around in a helical fashion, creating a rigid hollow cylinder, as shown in this section here. Now, what about the actual protein involved in the structure? So, if we actually examine the tail like flagella section, it's composed of a single protein flagellin.