Cellular Signaling Ch. 11

Signal Transduction Pathway First evolved in prokaryotes

Signal Types Local Signaling Long Distance – hormonal Paracrine Synaptic Long Distance – hormonal

Three Stages of Signaling Reception Ligands Only specific cells respond Transduction Response

Common Components Protein kinase Phosphatase Phosphorylation Cascade Amplify response Scaffolding Protein

Types of Receptors Intracellular receptors Receptors in the cellular membrane G Protein linked receptors Receptor tyrosine kinases Ion channel receptors

Second Messengers Small, non-protein water-soluble ions that send messages. Amplify signal because many can be produced following primary messenger molecule cAMP (cyclic adenosine monophosphate) Formed from ATP when adenylyl cyclase is activated Stimulates glycogen breakdown by activating protein kinase A Broken down by phosphodiesterase

cAMP

Second Messengers Ca++ and IP3 (inositol triphosphate) - Ca++ causes muscle cell contraction, cell division, and secretion of substances. Cytosolic concentrations maintained by pumps (to endoplasmic reticulum & mitochondria). A G protein activates phospholipase C, which breaks PIP2 into DAG (diacylglycerol) and IP3. IP3 opens the Ca++ gates, thereby activating proteins and causing cellular responses.

Types of Responses Cytoplasmic responses Nuclear responses