3Gap junctions between animal cells Plasmodesmata between plant cells Fig. 11-4Plasma membranesGap junctionsbetween animal cellsPlasmodesmatabetween plant cells(a) Cell junctionsFigure 11.4 Communication by direct contact between cells(b) Cell-cell recognition
4(a) Paracrine signaling (b) Synaptic signaling Fig. 11-5abLocal signalingTarget cellElectrical signalalong nerve celltriggers release ofneurotransmitterNeurotransmitterdiffuses acrosssynapseSecretingcellSecretoryvesicleFigure 11.5 Local and long-distance cell communication in animalsLocal regulatordiffuses throughextracellular fluidTarget cellis stimulated(a) Paracrine signaling(b) Synaptic signaling
5Long-distance signaling In long-distance signaling, animals and plants use chemical messengers called hormones.Hormones are chemicals made in one area of the body that are delivered to other areas.
6Long-distance signaling Fig. 11-5cLong-distance signalingEndocrine cellBloodvesselHormone travelsin bloodstreamto target cellsFigure 11.5 Local and long-distance cell communication in animalsTargetcell(c) Hormonal signaling
7What are Signal transduction pathways? A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response.In general there are 3 steps:1) Reception2) Transduction3) Response
9Plasma membrane 1 Reception Transduction Receptor Signaling molecule 1 FigEXTRACELLULARFLUIDCYTOPLASMPlasma membrane11Reception2TransductionReceptorRelay molecules in a signal transduction pathwayFigure 11.6 Overview of cell signalingSignalingmolecule
10Plasma membrane 1 Reception Transduction Response Receptor Activation FigEXTRACELLULARFLUIDCYTOPLASMPlasma membrane1Reception2Transduction3ResponseReceptorActivationof cellularresponseRelay molecules in a signal transduction pathwayFigure 11.6 Overview of cell signalingSignalingmolecule
11Step 1: receptionIn Step 1, Reception: a signaling molecule binds to a receptor protein, causing it to change shape.Ligand: the signaling moleculeReceptor: a molecule (usually a protein) on the surface of a cell that recognizes and binds to a ligandThe binding between a ligand and its’ receptor is highly specific.
17Step 2: TransductionIn Step 2, Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cellTransduction: the conversion of a signal outside the cell to a form that can bring about a specific cellular response.
18Signal Transduction Pathways Signal transduction usually involves multiple steps, called a signal cascade.Multi-step pathways (signaling cascades) can amplify a signal; even just a few molecules can cause a large cell response.Advantage: multi-step pathways can provide for more ways to coordinate and regulate the response.Multi-step pathways also allow for more specificity in the response.
24First messenger Adenylyl cyclase G protein GTP G protein-coupled FigFirst messengerAdenylylcyclaseG proteinG protein-coupledreceptorGTPATPSecondmessengercAMPFigure cAMP as second messenger in a G-protein-signaling pathwayProteinkinase ACellular responses
26EXTRACELLULAR FLUID Plasma membrane Ca2+ pump ATP Mitochondrion FigEXTRACELLULARFLUIDPlasmamembraneCa2+ pumpATPMitochondrionNucleusCYTOSOLCa2+pumpEndoplasmicreticulum (ER)Figure The maintenance of calcium ion concentrations in an animal cellCa2+pumpATPKeyHigh [Ca2+]Low [Ca2+]
27Step 3: ResponseIn Step 3, Response: Cell signaling leads to regulation of transcription or a change in the cell’s activities. This is sometimes called the “output response”.Transcription: One of the processes involved in genes that determines which proteins will be made in the cellOther cell signaling pathways may regulate the action of an enzyme.
28Growth factor Reception Receptor Phosphorylation cascade Transduction FigGrowth factorReceptionReceptorPhosphorylationcascadeTransductionCYTOPLASMInactivetranscriptionfactorActivetranscriptionfactorFigure Nuclear responses to a signal: the activation of a specific gene by a growth factorResponsePDNAGeneNUCLEUSmRNA
29The stimulation of glycogen breakdown by epinephrine: FigReceptionBinding of epinephrine to G protein-coupled receptor (1 molecule)TransductionInactive G proteinThe stimulation of glycogen breakdown by epinephrine:Active G protein (102 molecules)This is an example of a phosphory-lationcascadeInactive adenylyl cyclaseActive adenylyl cyclase (102)ATPCyclic AMP (104)Inactive protein kinase AActive protein kinase A (104)Figure Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrineInactive phosphorylase kinaseActive phosphorylase kinase (105)Inactive glycogen phosphorylaseActive glycogen phosphorylase (106)ResponseGlycogenGlucose-1-phosphate(108 molecules)
30Changes in signal transduction pathways Changes in signal transduction pathways can alter cellular response.For Example: Conditions where signal transduction is blocked or defective can be deleterious (bad), preventative, or prophylactic (good).
31What would happen if one of the relay molecules was defective? Fig. 11-UN1What would happen if one of the relay molecules was defective?1Reception2Transduction3ResponseReceptorActivationof cellularresponseRelay moleculesSignalingmolecule
32Question: how does caffeine work on the brain? Caffeine has many effects on the body, but the most noticeable is that it keeps us awake.The caffeine molecule is large and polar, so it doesn’t diffuse easily across the cell membrane.Instead it binds to receptors on the surfaces of nerve cells in the brain.
33adenosineAdenosine (a nucleoside) accumulates in the brain when a person is under stress or has prolonged mental activity.When it binds to a specific receptor in the brain, adenosine sets in motion a signal transduction pathway that results in reduced brain activity, which usually means drowsiness.
34Caffeine and adenosine Caffeine has a 3-dimensional structure similar to adenosine and is able to bind to the adenosine receptor.Because its binding does not activate the receptor, caffeine functions as a antagonist of adenosine signaling, with the result that the brain stays active.CaffeineAdenosine
35caffeineBecause caffeine has bound to the adenosine receptor, the adenosine has little effect, and the person stays awake.The binding of caffeine to the adenosine receptor, however, is a reversible reaction. In time, the caffeine molecules come off the adenosine receptors in the brain, allowing adenosine to bind once again.
36Additional effects of caffeine In addition to competing with adenosine for a membrane receptor, caffeine blocks the enzyme cAMP phosphodiesterase.This enzyme breaks down cAMP, which is a second messenger in the pathway that turns glycogen into sugar which is then released into the bloodstream.Can you see how caffeine increases the “fight or flight” response?