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Unformatted text preview: Chapter 11 - Cell Chapter Communication Communication 12/03/09 12/03/09 1 Introduction Cell Cell communication is the process by which cells detect, process, and respond to chemical signals to Cell signaling is used for many process Cell ranging from mating (yeast cells) to the regulation of hormones regulation In short, cell signaling is needed for all life IMPORTANT!!: Receptors are the only IMPORTANT!!: reason why cell communication is possible
12/03/09 12/03/09 2 Local Signaling Within Within short distances, cells release local regulators to target specific receptors regulators
Target cell Electrical signal along nerve cell triggers release of neurotransmitter Secretory vesicle Neurotransmitter diffuses across synapse Local regulator diffuses through extracellular fluid (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. Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. 3 12/03/09 12/03/09 Long Distance Signaling By By using a medium, such as blood (animals) in the bloodstream, hormones are secreted to target specific receptors elsewhere in the body Long-distance signaling Endocrine cell Blood vessel Hormone travels in bloodstream to target cells Target cell 12/03/09 12/03/09 (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells. 4 Cell Signaling
EXTRACELLULAR FLUID 3 Stages:
2. 2. CYTOPLASM Plasma membrane 1. Reception – detection of 1. Reception outside the cell Transduction outside a signal coming from Response Receptor Transduction – binding of the signal molecule to Activation a receptor protein, causing a process by which the of cellular signal is converted to a form that can bring about a response specificRelay molecules in a signal transduction pathway specific cellular response. Sometimes Sometimes Signal molecule occurs in a single step but requires a sequence of changes in a series of molecules via a signal-transduction pathway signal-transduction 3. 3. Response – cellular response (i.e. enzyme catalysis, gene activation) catalysis,
5 12/03/09 12/03/09 Signal Reception and Transduction Signal Initiation Initiation Signal Signal molecules act like a ligand, a small molecule that specifically binds to a larger one, when binding to larger receptor proteins (i.e. G-protein-linked receptors, tyrosine-kinase receptors, and ligandtyrosine-kinase gated ion-channel receptors) 12/03/09 12/03/09 6 G-protein-linked Receptor 1. Inactive form- absence of signal molecule 2. Active form- signal molecule binds to receptor, activating G-protein by 2. displacing GDP with GTP 3. G-protein moves across plasma membrane to activate enzyme, triggering 3. cellular response 4. Return to inactive form- signal molecule is no longer present, causing 4. hydrolyzed GDP to move back to beginning of inactive state hydrolyzed 1->2 3->4 12/03/09 12/03/09 7 Tyrosine-kinase Receptor Tyrosine-kinase 1. Inactive Form- absence of signal molecules 1. 2. Signal Binding- 2 signal molecules attach to their binding sites to form a 2. dimer (2 polypeptide aggregate) dimer 3. Active Form- ATP phosphorylation activates tyrosine-kinase receptors 4. Once activated, relay proteins binds to a receptor and undergoes 4. structural change that activates it, initiating signal-transduction pathway to cause cellular response 1->2 3->4 12/03/09 12/03/09 8 Ligand-gated Ion Channels 1. Binding of signal molecule (ligand) will cause 1. structural change of channel protein structural 2. Once binded, ion channel remains opened as 2. ions diffuse. After ion concentration reaches a certain level, a cellular response is triggered and causes the release of signal molecule causes 3. Ligand dissociates and channel protein returns to 3. original close shaped (inactive form) original 1. 2. 3. 12/03/09 12/03/09 9 Signal Transduction Pathways After After signal reception, the receptor activates another protein, which activates another molecule, and so on, until the protein that produces the final cellular response is activated response Molecules that relay a signal from receptor Molecules to response are called relay molecules relay 12/03/09 12/03/09 10 Phosphorylation Cascade
Signal molecule Once signal molecule binds to receptor, activated relay Once Receptor Activated relay molecule activates protein kinase 1. molecule ActiveInactive Active protein kinase 1 transfer a phosphate from ATP protein kinase Active 1 to activate protein kinase 2 (inactive). protein kinase 1 This transferInactive phosphorus (phosphorylation) then of This protein kinase cascades down to ATP ADP kinase 3 which activates a protein Active P 2 protein kinase protein that triggers PP cellular response a protein P 2
la ory ph os Ph nc tio as de ca
i Inactive protein kinase 3 Pi ATP ADP PP Inactive protein Active protein kinase 3 ATP ADP Pi PP P P Active protein Cellular response 11 12/03/09 12/03/09 Cyclic AMP (cAMP) Cyclic AMP acts a second messenger, or nonprotein, water-soluable Cyclic molecule, and is converted from ATP by adenylyl cyclase built into the plasma membrane plasma The signal molecule (first messenger) activates a G-protein-linked receptor, The causing a specific G-protein to activate adenylyl cyclase which then catalyzes ATP to cAMP catalyzes The cAMP (second messenger) then activates another protein, usually The protein kinase A, which triggers a specific cellular response protein 12/03/09 12/03/09 12 Cell Communication in Action - A Larger View: Calcium and Cell Inositol Trisphosphate in Signaling Pathways Inositol Reception- A signal molecule binds to G-protein linked receptor/Tyrosinekinase receptor and activates both Transduction- In G-protein linked, G protein activates Phospholipase C In while Phospholipase C binds to a Tyrosine receptor to cleave PIP2 into diacylglycerol (DAG) and second messenger inositol trisphosphate (IP3) diacylglycerol IP3 binds ligand-gated calcium channel in ER and allows calcium ions to IP3 diffuse into cytosol, activating other proteins via calmodulin (calcium binding protein) protein) Cellular Response 12/03/09 12/03/09 13 Specificity of Cell Signaling Particular proteins a cell possesses determine Particular what signal molecules it responds to and the response response Response 1- Pathway leads to a single Response response response Response 2,3- Pathway branches: leads to 2 Response responses responses Response 4- Cross-talk occurs between the 2 Response pathways: second relay molecule regulates the first first Response 5- Receptor is different from other Response cells cells 12/03/09 12/03/09 14 ...
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- Cell Signaling