1. Cell Communication
CHAPTER 11

2. An Example of Cell Communication: Fight or Flight Response

3. Cell Signaling Animal cells communicate by:
Direct contact (gap junctions)
Secreting local regulators (growth factors, neurotransmitters)
Long distance (hormones)
Chemical and Electrical signals

4. Types of Communication:
Autocrine- receptor on same cell (growth factors telling tumor cells to keep growing)
Paracrine- neighboring cell is near signal releasing cell (two neurons)
Juxtacrine- target and releasing cells are in physical contact (quorum sensing in bacteria, gap junctions)
- Endocrine- chemicals that need to travel long distances (hormones)

5. Signal Transduction Pathway
Series of steps by which a signal on a cell’s surface is converted to a specific cellular response
Signaling can be short distance or long distance

6. 3 Stages of Cell Signaling:
Reception: A signal molecule (ligand) binds to a receptor protein causing it to change shape
Transduction: series of molecules interactions that relay signal from receptor to target molecule
Response: regulation of transcription or cytoplasmic activities

7. 1. Reception
Binding between signal molecule (ligand) + receptor is highly specific.
Receptors found in:
Intracellular receptors (cytoplasm, nucleus)
hydrophobic ligands
Eg. testosterone or other hormones turning on and off certain genes
Plasma membrane receptor
water-soluble ligands

8. G-Protein-Coupled Receptor
2 min

9. Tyrosine Receptor Kinase
1 min

10. Ligand-Gated Ion Channel
2 minutes

11. Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
7 transmembrane segments in membrane
Attaches (P) to tyrosine
Signal on receptor changes shape
G protein + GTP activates enzyme  cell response
Activate multiple cellular responses at once
Regulate flow of specific ions
(Ca2+, Na+)

12. 2. Transduction
Cascades of molecular interactions relay signals from receptors  target molecules; “dominoes effect”
Protein kinase: enzyme that phosphorylates and activates proteins at next level
Phosphorylation cascade: enhance and amplify signal

14. Second Messengers
small, nonprotein molecules/ions that can relay signal inside cell
Eg. cyclic AMP (cAMP) and Ca2+
- cAMP is made when adenyl cyclase converts ATP to cAMP
- cAMP activates protein kinase A which phosphorylates other proteins

15. 3. Response
Regulate protein synthesis by turning on/off genes in nucleus (gene expression)
Regulate activity of proteins in cytoplasm

16. G-Protein-coupled Receptors
Figure 6-11: The G protein-coupled adenylyl cyclase-cAMP system

17. Transduction Reviewed
Figure 6-14: Summary of signal transduction systems