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Transcript
Cell Communication Reception, Transduction, Response Local signals • Cells in a multicellular organism communicate by chemical messengers • In local signaling, animal cells may communicate by direct contact, or cell-cell recognition Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Local signals cont’d • local regulators - messenger molecules that travel short distances • Paracrine signaling – local regulator released directly onto one cell by another • Synaptic signaling – a nerve signal triggers the release of a local regulator onto a near by cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Long Distance Signaling • Hormones – chemical messengers that travel long distance. • Ex. Through blood vessels Signal Transduction Pathway • After a signal is received a signal transduction pathway is a set of step that trigger a certain response from a cell. 1 Reception 2 transduction 3 response** • Ex. Yeast mating Reception • Reception – delivery of a signal to a cell • Signal molecules are called ligands (ex.hormones) • Water soluble ligands must bind to receptor proteins in the cell membrane • Non-polar or small ligands can travel directly in the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings G protein-coupled receptor • G protein-coupled receptor – membrane receptor that activates a G protein when a ligand is present. (starts transduction) • G protein – When activated, uses energy from GDP becoming GTP to turn on an enzyme. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Receptor Tyrosine Kinase • Receptor tyrosine kinase - membrane receptors that attach phosphates to tyrosines. • When the ligand is present the two kinases form a dimer and can trigger multiple transduction pathways. Gated Ion Channels • ligand-gated ion channel – receptor opens like a gate when a ligand is present to allow ions in. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 11-7d 1 Signaling molecule (ligand) Gate closed Ligand-gated ion channel receptor 2 Ions Plasma membrane Gate open Cellular response 3 Gate closed Intracellular (internal) Receptors • Small or hydrophobic ligands travel directly through the cell membrane. • They join to an internal receptor to form a hormone receptor complex (which begins transduction) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Transduction • Signal transduction usually involves multiple steps that includes turning a sequence of proteins on and off to get a response from the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phosphorylation/Dephosphorylation • Phosphorylation – add phosphates (turns protein on) • Dedphosphorylation – removes phosphates (turns proteins off) • Protein kinases – does phosphorylation • Protein phosphatases- does dephosphorylation Phosphorylation Cascade Second Messengers • Second messengers – small molecules that diffuse throughout the cell to carry the signal during transduction. • Second messengers, cAMP (made from ATP), IP3, Ca+, DAG** Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 11-13-2 EXTRACELLULAR FLUID Signaling molecule (first messenger) G protein DAG GTP G protein-coupled receptor Phospholipase C PIP2 IP3 (second messenger) IP3-gated calcium channel Endoplasmic reticulum (ER) CYTOSOL Ca2+ Ca2+ (second messenger ) Response • Cell usually respond by synthesizing enzymes or proteins, or turning genes on or off. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 11-14 Growth factor Reception Receptor Phosphorylatio n cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor P Response DNA Gene NUCLEUS mRNA Fig. 11-15 Reception Binding of epinephrine to G protein-coupled receptor (1 molecule) Transduction Inactive G protein Active G protein (102 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (102) ATP Cyclic AMP (104) Inactive protein kinase A Active protein kinase A (104) Inactive phosphorylase kinase Active phosphorylase kinase (105) Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response Glycogen Glucose-1-phosphate (108 molecules) Apoptosis • Apoptosis – A response that is a programmed or controlled cell suicide • A cell is chopped and packaged into vesicles that are digested to prevent enzymes from leaking out and damaging other cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Triggering Apoptosis • Apoptosis can be triggered by: – An extracellular death-signaling ligand – DNA damage in the nucleus – Protein misfolding in the endoplasmic reticulum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1. Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system 2. Compare and contrast G protein-coupled receptors, tyrosine kinase receptors, and ligand-gated ion channels 3. List two advantages of a multistep pathway in the transduction stage of cell signaling 4. Explain how an original signal molecule can produce a cellular response when it may not even enter the target cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5. Define the term second messenger; briefly describe the role of these molecules in signaling pathways 6. Explain why different types of cells may respond differently to the same signal molecule 7. Describe the role of apoptosis in normal development and degenerative disease in vertebrates Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings