Cell surface molecule

Biological cells are the fundamental units of life, and an extraordinary array of specialized cells have evolved to accomplish the many different tasks required of organisms in their environments. In order for specialized cells to interact with each other and their environments, they must bring things in, release other things, sense pressure, and, in some cases, recognize other cells. All of these functions require cells to have lots of unique molecules on their surfaces (see: cell membrane). In fact, imagine a pin cushion with thousands and thousands of pins. Some are green, some are blue. Some are sticky. Some have flat heads, some have round heads, some are pushed all the way in, some are sticking out. Some of the pins are needles, little pipes, or channels that let things into and out of the cell.

Some of the various kinds of cell surface molecules:
 * poron - see aquaporin
 * channel - see ion channel
 * pump - see transmembrane transport proteins
 * receptor
 * desmosome
 * cadherin
 * signal protein - see list of types of proteins