1. Signaling Machinery The Signals The Receivers
Peptides & small organic molecules (hormones, amines)
Signaling molecules are called ligands in general
The Receivers
Large proteins (protein complexes)
Ligand binding alters conformations resulting in conveyance of signal

2. A Ligand Bound to Its Receptor
Figures\Chapter15\High-Res\life7e-fig jpg

3. Cell Signaling Cell A Cell B Changes in Cell Fate Differentiation
Ligand
activates
receptor
Ligand
secreted
Receptor
Cell A
Modulate activity of existing proteins
Cell B
Signaling cascades initiated
Protein synthesis
Gene Activation
Changes in Cell Fate Differentiation
Migration
Proliferation

4. Categories of Signaling Molecules
Growth factors (proliferation/differentiation)
FGF, EGF, TGF, NGF, peptide hormones
Retinoids/Steroids
RA, Testosterone, Cortisone
Differentiation
Wnt, Hedgehog, Delta
Cytokines
Interferons, interleukins
Migration
Semaphorins, Ephrins
Neurotransmitters
Catecholamines, NO
Other
Odorants, capsaicin

5. Categories of Receptors
Cytoplasmic/Nuclear
Bind membrane soluble ligands – steroids/retinoids
Directly affect transcription
Transmembrane
Receptor tyrosine kinases – growth factors
Receptor serine kinases – growth factors
Kinase-associated receptors - cytokines
Seven-pass – neurotransmitters, peptide hormones
Ligand-gated channels – neurotransmitters, ions
Other – cell-associated ligands

6. Signaling Modes Autocrine Juxtacrine Paracrine
Signal is received by secreting cell (as well as other cells)
Juxtacrine
Signal is transmitted only short distances to neighboring cells
Signaling molecule is membrane anchored or associated with ECM
Paracrine
Signaling at a distance from source
Growth factors, hormones, cytokines, etc.
Figures\Chapter15\High-Res\life7e-fig jpg

7. Two Locations for Receptors
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8. A Cytoplasmic Receptor
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9. A Gated Ion Channel
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10. A Protein Kinase Receptor
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11. A Protein Kinase Cascade
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12. G-Protein-Linked Receptor (7 Pass)
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2nd messenger

13. 7-Pass Receptor Interacting with Trimeric G-Protein

14. Formation of Cyclic AMP 2nd Messenger
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15. Phospholipid Derived 2nd Messengers

16. IP3 and DAG 2nd Messengers
phosphotidylinositol-4,5 - bisphosphate
diacylglycerol
Inositol-1,4,5-phosphate
Figures\Chapter15\High-Res\life7e-fig jpg

17. Calcium Ions as a 2nd Messengers
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18. Nitric Oxide as a 2nd Messenger
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19. Signal Transduction Pathway Opens Ion Channels
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20. Signal Transduction Pathway Opens Ion Channels
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21. Signaling Cascades Alter Enzyme Activity
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22. Gap Junctions Connect Some Animal Cells
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23. Plasmodesmata Connect Some Plant Cells
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