The antennas, doors and bridges of the cell
Receptors and transport channels
The human body is literally a society of cells, living somewhat in harmony. Just like a community of people living in a social structure, interacting, communicating and bonding with each other, cells are not very different. They accomplish this via proteins molecules dispersed on the cell surface. To mention a few – signalling molecules like GPCRs (G Protein Coupled Receptor) and RTKs (Receptor Tyrosine Kinase) act like the antennas transmitting information into the cell from the outside; membrane transport channels act like doors, allowing specific molecule to move in or out; cell adhesion molecules, Cadherins and Integrins, act like bridges connecting the cells to one another or to the extracellular matrix, keeping the cells in place. There exist hundreds of such proteins on the surface, making them a fully functional unit.