The Antennas, Doors and Bridges of The Cell
The human body is literally like a society of cells, living somewhat in harmony. Similar to 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 protein 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 like cadherins and integrins, act like bridges connecting the cells to one another, or to the extracellular matrix, and keep the cells in place. There exist hundreds of such proteins on the surface, making them a fully functional unit.