cell communication chapter 11. 11.1 external signals are converted to responses within a cell
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Cell CommunicationChapter 11
11.1External signals are converted to responses within a cell
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
Signaling by Distance
Cell to cell contact
Local◦Paracrine◦Synaptic
Long distance◦Endocrine
Signal Transduction Pathways
Receiving end of cell “conversation”
11.2Reception: A signaling molecule binds to a receptor protein, causing it to change shape
Reception
Chemical signal is detected by the target cell
Surface proteins or intracellular receptor
Ligand◦Signaling molecule that
binds specifically to another molecule
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
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
Reception: Ion Channel Receptors
Ligand gated ion channel changes shape when ligand binds
Opens “gate” so ions can cross membrane
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
11.3Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell
Transduction
Converts the signal to a form that the cell can respond to
Often involves relay molecules
Transduction: Phosphorylation Cascades
Series of proteins activated by addition of phosphate group pass signal along
Like falling dominoes
Transduction: Secondary Messengers
Non-protein messengers pass signal along◦Ex: cyclic AMP (cAMP), Ca+, or IP3
11.4Response: Cell signaling leads to regulation of transcription or cytoplasmic activities
Response
Specific response by the cell
Almost any imaginable cellular activity turned on or off, depending on signal
Usually regulate enzyme activity
Response: Nuclear
Genes turned on to make proteins◦Activates
transcription
Genes turned off to stop making proteins◦Stops
transcription
Response: Cytoplasmic
Proteins made are modified, amplified, or terminated◦Translation of genes
modified, resulting proteins modified
Example: stimulation of glycogen breakdown by epinephrine
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
11.5Apoptosis integrates multiple cell-signaling pathways
Apoptosis
Programmed cell deathPart of normal development and
differentiation◦Ex: formation of fingers and toes◦Ex: cancer cells
Complex cell signaling pathways
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