cell communication chapter 11. 11.1 external signals are converted to responses within a cell
TRANSCRIPT
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Cell CommunicationChapter 11
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11.1External signals are converted to responses within a cell
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Why cell communication?
Cells must “talk” to coordinate activities
Evolved in single and multicellular organisms◦Ex: quorum sensing
in bacteria◦Ex: hormones in
plants and animals
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Signaling by Distance
Cell to cell contact
Local◦Paracrine◦Synaptic
Long distance◦Endocrine
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Signal Transduction Pathways
Receiving end of cell “conversation”
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11.2Reception: A signaling molecule binds to a receptor protein, causing it to change shape
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Reception
Chemical signal is detected by the target cell
Surface proteins or intracellular receptor
Ligand◦Signaling molecule that
binds specifically to another molecule
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Reception: G Protein-Coupled Receptor
Ligand binds to G protein-coupled receptor on membrane
G protein becomes activated
Activated G protein binds to enzyme, activating it
G protein receptor is COUPLED with G protein
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Reception: Receptor Tyrosine Kinases
Ligand binds to receptor tyrosine kinase protein monomers◦Kinase: enzyme that
transfers phosphate groups
Activated monomers form dimer
Phosphates from ATP added to activated dimer
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Reception: Ion Channel Receptors
Ligand gated ion channel changes shape when ligand binds
Opens “gate” so ions can cross membrane
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Reception: Intracellular Receptors
Receptor in cytoplasm or nucleus (NOT cell membrane)
Signal is hydrophobic or small enough to cross membrane◦Ex: steroid hormones, nitric
oxide
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11.3Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell
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Transduction
Converts the signal to a form that the cell can respond to
Often involves relay molecules
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Transduction: Phosphorylation Cascades
Series of proteins activated by addition of phosphate group pass signal along
Like falling dominoes
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Transduction: Secondary Messengers
Non-protein messengers pass signal along◦Ex: cyclic AMP (cAMP), Ca+, or IP3
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11.4Response: Cell signaling leads to regulation of transcription or cytoplasmic activities
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Response
Specific response by the cell
Almost any imaginable cellular activity turned on or off, depending on signal
Usually regulate enzyme activity
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Response: Nuclear
Genes turned on to make proteins◦Activates
transcription
Genes turned off to stop making proteins◦Stops
transcription
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Response: Cytoplasmic
Proteins made are modified, amplified, or terminated◦Translation of genes
modified, resulting proteins modified
Example: stimulation of glycogen breakdown by epinephrine
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Cell Signaling Specificity
Which receptors and secondary messengers a cell has determines which signals it will respond to and how◦Ex: liver and heart cells respond differently to
epinephrine
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11.5Apoptosis integrates multiple cell-signaling pathways
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Apoptosis
Programmed cell deathPart of normal development and
differentiation◦Ex: formation of fingers and toes◦Ex: cancer cells
Complex cell signaling pathways