320Fall10Lecture13 - 1 BIO 320 Cell Biology, Fall 2010 Dr....

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BIO 320 Cell Biology, Fall 2010 Dr. Thomas Bushart Week 13 1
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Cell communication Cells (especially in multicellular organisms) need to send and receive information I Even bacteria can coordinate behavior through “quorum sensing” Is there anything out there? 2
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General mechanism Various molecules, proteins, and enzymes form a signaling pathway 3
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Perception by receptors A cell must be able to interact with a stimulus I Chemical receptors I Also light (phytochrome for example) and physical Help! I can’t sense anything! 4
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Local signaling Physical contact Limited diffusion, rapid removal, antagonists I Like binding by heparin sulfate proteoglycans 5
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Long distance Long cells or highly mobile signals 6
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Signaling speed Neurons are fast I Electrical signal is rapid I Synapse is small I Neurotransmitter concentration is high Ligand binding can be weak, easily turned off Endocrine signaling is slow I Transport of chemicals through bloodstream I Dilution requires high affinity, harder to modulate Cellular response I Modification of existing elements = fast I Changes in gene expression = slow 7
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Response comparison 8
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Gap junction signaling Intracellular signaling molecules like Ca 2+ or cAMP (cyclic AMP) I 2-way diffusion homogenizes responses Neighboring cells can coordinate behaviors I Liver cells Typical in plant cells (plasmodesmata) 9
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Autocrine signaling Paracrine signaling to same targets I A cell can reinforce its own behavior I Similar cells can act in concert 10
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Cells are specialized Each cell type will have a unique ability to sense signals I Does it have a receptor? Different signal combinations can modify that cell’s behavior I Some signals needed for continued survival 11
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Different responses Same signal can have different outcomes I Receptor or internal pathway 12
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Concentration dependence Amount of signal may change effects I Morphogens and gradients during development (Twist expression from chapter 22 ) 13
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Changes in signaling Turnover impacts rapidity of response changes 14
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Activation of pathways Responses can be direct – more signal leads to an equally greater response Responses can be more abrupt 15
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Switch-like responses Simultaneous inhibition of a contrary pathway I Adrenaline (epinephrine) increases cAMP in muscle cells Promotes glycogen breakdown Inhibits glycogen synthesis More than one effector molecule required Feedback I M-Cdk activation 16
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Effector number impacts Sharpness of response depends on the number of required effector molecules 17
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Enzymatic feedback Threshold activation promotes runaway activity I Action potentials Positive feedback can promote activity even after withdrawal of stimulus I “Memory” I Muscle cell regulatory genes promote their own transcription 18
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Feedback and delays 19
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Adaptation/Desensitization Generally a delayed negative feedback I Increased responsiveness to changes 20
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320Fall10Lecture13 - 1 BIO 320 Cell Biology, Fall 2010 Dr....

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