1. Chapter 11 – Cell Communication

2. 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

3. Signal Transduction Pathway

4. 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

5. Cell Signalling

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

7. 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

8. 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

9. 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

10. 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)
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11. Response Cytoplasmic response Regulate the activity of enzymes
Example breakdown of glycogen into glucose-1-phosphate
Also an example of signal amplification
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12. Response Nuclear response Regulate the synthesis of proteins
Example: transcription factors
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