Membrane proteins fall into two major categories— peripheral and integral.Peripheral proteins associate with phospholipid heads or hydrophilic domains of integral proteins by non-covalent interactions.Many peripheral proteins participate in cell signaling cascades as they can easily detach from the membrane. Other peripheral proteins link the membrane with the cytoskeleton, providing structural support.Integral proteins are amphipathic molecules with their hydrophilic regions facing the cytoplasm or extracellular fluid and the hydrophobic domain embedded within the phospholipid tails. Transmembrane proteins are a type of integral protein that span the entire plasma membrane. They often play important roles in the cell, including serving as transporters, enzymes, and receptors.The membrane-spanning parts of these proteins can be a single alpha helix, multiple alpha helices, or a larger beta barrel that has a pore through the center.Lipid-anchored proteins have attached lipid chains that fasten them to the membrane.