Cell CommunicationEvolution of Cell Signaling Communication Between Mating Yeast CellsCells CommunicationDirect ContactCell Communication In AnimalsCell SignalingReceptionReceptorsIntracellular Receptors Steroid hormone interacting with an intracellular receptorSurface ReceptorsChemically Gated Ion ChannelsEnzymatic ReceptorsReceptor Tyrosine KinasesG-protein-linked ReceptorsSlide 17Second MessengersSignal Transduction Pathways A Phosphorylation CascadecAMP Second Messenger G-protein-signaling pathwayCyclic AMPSlide 23Calcium (Ca++) PathwaysCalcium ions and Inositol Triphosphate (IP3)Ca++ PathwayCalcium and IP3 in signaling pathwaysFine-Tuning of the ResponseAmplificationCytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrineSpecificity of Cell SignalingSignaling Efficiency: Scaffolding Proteins and Signaling ComplexesSlide 33Cell CommunicationCell CommunicationEvolution of Cell SignalingEvolution of Cell Signaling•A signal-transduction pathway is a series of A signal-transduction pathway is a series of steps by which a signal on a cell’s surface is steps by which a signal on a cell’s surface is converted into a specific cellular responseconverted into a specific cellular response•Signal transduction pathways convert signals on Signal transduction pathways convert signals on a cell’s surface into cellular responsesa cell’s surface into cellular responses•Pathway similarities suggest that ancestral Pathway similarities suggest that ancestral signaling molecules evolved in prokaryotes and signaling molecules evolved in prokaryotes and have since been adopted by eukaryoteshave since been adopted by eukaryotesCommunication Between Mating Yeast CellsCommunication Between Mating Yeast Cells factorReceptor Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. Mating. Binding of the factors to receptors induces changes in the cells that lead to their fusion. New a/ cell. The nucleus of the fused cell includes all the genes from the a and  cells. factorYeast cell,mating type aYeast cell,mating type a/aa132Cells CommunicationCells Communication•Direct contactDirect contact•Paracrine signalingParacrine signaling•Endocrine signalingEndocrine signaling•Synaptic signalingSynaptic signalingDirect ContactDirect Contact•Cells touch each other and signal molecules travel through Cells touch each other and signal molecules travel through special connections called communicating junctionsspecial connections called communicating junctions•Communicating junctions link the cytoplasms of 2 cells together, Communicating junctions link the cytoplasms of 2 cells together, permitting the controlled passage of small molecules or ions permitting the controlled passage of small molecules or ions between them. between them. Plasma membranesGap junctionsbetween animal cellsCell junctionsCell-cell recognitionPlasmodesmatabetween plant cells(a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.Hormone travelsin bloodstreamto target cells (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells.Local regulator diffuses through extracellular fluidSecretingcellTarget cellSecretoryvesicleElectrical signalalong nerve celltriggers release ofneurotransmitterNeurotransmitter diffuses acrosssynapseTarget cellis stimulatedLocal signaling Long-distance signalingEndocrine cellBloodvesselTargetcellCell Communication In AnimalsCell Communication In Animals•In many other cases, animal cells communicate using local In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distancesregulators, messenger molecules that travel only short distances•In long-distance signaling, plants and animals use chemicals called In long-distance signaling, plants and animals use chemicals called hormoneshormonesCell SignalingCell SignalingEXTRACELLULARFLUIDReceptorSignal moleculeRelay molecules in a signal transduction pathway Plasma membraneCYTOPLASMActivationof cellularresponseReception Transduction Response1 2 3•The cells of a organism communicate with each other by releasing The cells of a organism communicate with each other by releasing signal moleculessignal molecules that that bind to bind to receptor proteinsreceptor proteins located either on or inside of located either on or inside of target cellstarget cells..•Three stages of cell signaling:Three stages of cell signaling:•Reception - each target cell has receptors that detect a specific signal molecule and binds to itReception - each target cell has receptors that detect a specific signal molecule and binds to it•Transduction – binding of the signal molecule changes the receptor protein in some way that Transduction – binding of the signal molecule changes the receptor protein in some way that initiates transduction or conversion of the signal to a form that can bring about a specific initiates transduction or conversion of the signal to a form that can bring about a specific cellular responsecellular response•Response – transduced signal triggers a specific cellular response, any cell activityResponse – transduced signal triggers a specific cellular response, any cell activityReceptionReception•A signal molecule binds to a receptor protein, A signal molecule binds to a receptor protein, causing it to change shapecausing it to change shape•The binding between signal molecule (ligand) The binding between signal molecule (ligand) and receptor is highly specificand receptor is highly specific•A conformational change in a receptorA conformational change in a receptor•Is often the initial transduction of the signalIs often the initial transduction of the signalReceptorsReceptors•Intracellular receptors Intracellular receptors •Some signal molecules that are small or hydrophobic can pass through Some signal molecules that are small or hydrophobic can pass through the plasma membrane and bind