Cell Communication Chapter 11

11.1 External 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 Why cell communication?

Signaling by Distance Cell to cell contact Local Long distance Paracrine Synaptic Long distance Endocrine Signaling by Distance

Signal Transduction Pathways Receiving end of cell “conversation” Signal Transduction Pathways

11.2 Reception: 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

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: G Protein-Coupled Receptor

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: Receptor Tyrosine Kinases

Reception: Ion Channel Receptors Ligand gated ion channel changes shape when ligand binds Opens “gate” so ions can cross membrane Reception: Ion Channel Receptors

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 Reception: Intracellular Receptors

11.3 Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell

Converts the signal to a form that the cell can respond to Often involves relay molecules Transduction

Transduction: Phosphorylation Cascades Series of proteins activated by addition of phosphate group pass signal along Like falling dominoes Transduction: Phosphorylation Cascades

Transduction: Secondary Messengers Non-protein messengers pass signal along Ex: cyclic AMP (cAMP), Ca+, or IP3 Transduction: Secondary Messengers

11.4 Response: 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

Response: Nuclear Genes turned on to make proteins Activates transcription Genes turned off to stop making proteins Stops transcription Response: Nuclear

Response: Cytoplasmic Proteins made are modified, amplified, or terminated Translation of genes modified, resulting proteins modified Example: stimulation of glycogen breakdown by epinephrine Response: Cytoplasmic

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 Cell Signaling Specificity

11.5 Apoptosis integrates multiple cell-signaling pathways

Apoptosis Programmed cell death Part of normal development and differentiation Ex: formation of fingers and toes Ex: cancer cells Complex cell signaling pathways Apoptosis