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Cell Communication CHAPTER 11
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An Example of Cell Communication: Fight or Flight Response
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Cell Signaling Animal cells communicate by:
Direct contact (gap junctions) Secreting local regulators (growth factors, neurotransmitters) Long distance (hormones) Chemical and Electrical signals
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Types of Communication:
Autocrine- receptor on same cell (growth factors telling tumor cells to keep growing) Paracrine- neighboring cell is near signal releasing cell (two neurons) Juxtacrine- target and releasing cells are in physical contact (quorum sensing in bacteria, gap junctions) - Endocrine- chemicals that need to travel long distances (hormones)
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Signal Transduction Pathway
Series of steps by which a signal on a cell’s surface is converted to a specific cellular response Signaling can be short distance or long distance
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3 Stages of Cell Signaling:
Reception: A signal molecule (ligand) binds to a receptor protein causing it to change shape Transduction: series of molecules interactions that relay signal from receptor to target molecule Response: regulation of transcription or cytoplasmic activities
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1. Reception Binding between signal molecule (ligand) + receptor is highly specific. Receptors found in: Intracellular receptors (cytoplasm, nucleus) hydrophobic ligands Eg. testosterone or other hormones turning on and off certain genes Plasma membrane receptor water-soluble ligands
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G-Protein-Coupled Receptor
2 min
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Tyrosine Receptor Kinase
1 min
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Ligand-Gated Ion Channel
2 minutes
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Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR) Tyrosine Kinase Ligand-Gated Ion Channels 7 transmembrane segments in membrane Attaches (P) to tyrosine Signal on receptor changes shape G protein + GTP activates enzyme cell response Activate multiple cellular responses at once Regulate flow of specific ions (Ca2+, Na+)
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2. Transduction Cascades of molecular interactions relay signals from receptors target molecules; “dominoes effect” Protein kinase: enzyme that phosphorylates and activates proteins at next level Phosphorylation cascade: enhance and amplify signal
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Second Messengers small, nonprotein molecules/ions that can relay signal inside cell Eg. cyclic AMP (cAMP) and Ca2+ - cAMP is made when adenyl cyclase converts ATP to cAMP - cAMP activates protein kinase A which phosphorylates other proteins
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3. Response Regulate protein synthesis by turning on/off genes in nucleus (gene expression) Regulate activity of proteins in cytoplasm
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G-Protein-coupled Receptors
Figure 6-11: The G protein-coupled adenylyl cyclase-cAMP system
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Transduction Reviewed
Figure 6-14: Summary of signal transduction systems
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