Cell Communication

Cells are continually receiving information from their surroundings, and they must be able to respond appropriately. Most extracellular chemical signals fall into one of three categories: (1) proteins and peptides; (2) peptide neurotransmitters; (3) and steroids and other membrane soluble molecules. Physical signals such as electromagnetic radiation (light) and heat are also important. Growth, proliferation, differentiation, movement, and programmed cellular death all depend upon signals altering a cell's physiology, often through the activation and repression of genes. Signals may induce transitory or permanent changes in cells.

Chemical signals specifically bind protein receptors found either on the plasma membrane or in the cell's cytoplasm. The signal pathways consist of a few nonprotein second messengers such as calcium ions (Ca²⁺), cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), diacylglycerol (DG) and inositol triphosphate (IP₃) which transduce or send the signal to the cellular components involved in the response.

Notes
Common second messengers are: cAMP, cGMP, Ca²⁺, DG, IP₃