The most common types of secondary protein structures are alpha helices and beta sheets. Alpha helices are right handed coils of amino acids that form helical structures, similar to a coiled tube. The hydrogen bonding pattern of an alpha helix keeps all of the hydrogen bonds within the interior of the coil. So if hydrophobic side chains are present, they are on the exterior of the coil. This makes alpha helices ideal protein subunits for crossing through cell membranes. The polar hydrogen bonds are protected on the inside and the hydrophobic side chains can interact with the nonpolar interior of the membrane.