1. Cell Communication
Chapter 11

2. 11.1
External signals are converted to responses within a cell

3. 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?

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

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

6. 11.2
Reception: A signaling molecule binds to a receptor protein, causing it to change shape

7. Reception Chemical signal is detected by the target cell
Surface proteins or intracellular receptor
Ligand
Signaling molecule that binds specifically to another molecule
Reception

8. 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

9. 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

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

11. 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

12. 11.3
Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell

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

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

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

16. 11.4
Response: Cell signaling leads to regulation of transcription or cytoplasmic activities

17. Response Specific response by the cell
Almost any imaginable cellular activity turned on or off, depending on signal
Usually regulate enzyme activity
Response

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

19. 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

20. 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

21. 11.5
Apoptosis integrates multiple cell-signaling pathways

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