Chapter 11 – Cell Communication

Signal-transduction pathway Signal on a cell’s surface is converted into a specific cellular response Local signaling (short distance): Paracrine (growth factors) Synaptic (neurotransmitters) Long distance: hormones

Signal Transduction Pathway

Cell Signaling Reception – target cell detection of a signal molecule, is detected when signal molecule binds to receptors surface Transduction – converts the signal to a form that can bring about a cellular response; can be a single-step or a series of changes (signal transduction pathway) Response – triggering of a specific cellular response

Cell Signalling

Membrane Receptors G-protein linked receptors GDP bound = inactive GTP bound = active Receptor is active when signal is attached Enzyme activated, GTP  GDP

Membrane Receptors Tyrosine kinases Kinases – phosphorylate Can trigger multiple cellular responses Signal binding causes dimer formation Adds phosphates Activates relay proteins to elicit cellular response

Membrane Receptors Ion channel receptors When signal is absent, gate closed Signal (ligand) binds – gate opens, ions move in, elicit cellular response Signal detaches closing the gate

Transduction Pathways Phosphorylation cascade Adding P from ATP to activate proteins Uses protein kinases Approx. 2% of our genes thought to code for protein kinases

Transduction Pathways Second messengers Non-protein pathways Example – cAMP (cyclic adenosine monophosphate) Includes a g-protein-linked receptor The cAMP activates another protein (usually kinase) Animation

Response Cytoplasmic response Regulate the activity of enzymes Example breakdown of glycogen into glucose-1-phosphate Also an example of signal amplification Animation

Response Nuclear response Regulate the synthesis of proteins Example: transcription factors animation