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 distinct regions that interact with both the interior and exterior of the cell, allowing them to facilitate the movement of molecules and ions. These proteins can be classified into different types based on their functions. For example, channel proteins form pores that allow specific substances to pass through, while receptor proteins bind to signaling molecules, triggering cellular responses. Overall, transmembrane proteins are essential for maintaining cellular homeostasis and communication.