Transmembrane protein

 A transmembrane protein is a protien with hydrophilic and hydrophobic regions which span thelipid bilayer. These proteins can either be 'single-pass' meaning it crosses the membrane once or 'multipass' and therefor cross the bilayer more than once. Transmembrane proteins are usually either single alpha helices, multiple alpha helices or a beta sheet that has been rolled and is referred to as a beta barrel[1].