Transmembrane proteins are integral membrane proteins that span across the lipid bilayer of cell membranes. They play crucial roles in various cellular functions, including transport, signaling, and maintaining the structure of the cell. These proteins have regions that are hydrophobic, allowing them to interact with the lipid environment, as well as hydrophilic regions that extend into the aqueous environments inside and outside the cell. These proteins can function as channels or carriers, facilitating the movement of ions and molecules across the membrane. Examples of transmembrane proteins include ion channels, receptors, and transporters, each contributing to essential processes such as communication and nutrient uptake in cells.