1. Cell Communication Lecture 4 Fall 2008

2. How do cells communicate?1
Quorum sensing, biofilm formation
Fig. 11.3

3. How do cells communicate?2
Signal Transduction Pathways
A mechanism linking a mechanical or chemical stimulus to a specific cellular response
Quorum sensing, biofilm formation
Fig. 11.2

4. Local and Long Distance Signaling: An Overview3
Local signaling – direct contact
Cell junctions connect cytoplasm
Cell-cell recognition
Interactions between cell surface molecules (e.g. glycoproteins, glycolipids)
Fig. 11.4

5. Local and Long Distance Signaling: An Overview4
Local signaling – messenger molecules
Local regulators
Messenger molecules that travel only a short distance
Paracrine signaling
Discharge of local regulators by one cell (secreting cell)
Acts on cells nearby
Synaptic signaling
Release of neurotransmitter molecules from a nerve cell to a target cell
Fig. 11.5
Fig. 6.21

6. Local and Long Distance Signaling: An Overview5
Long distance signaling
Endocrine signaling
Hormones released into bloodstream
Travel to target cell
Fig. 11.5

7. Overview of Cell Signaling6
Overview of Cell Signaling
Three stages
Reception
Transduction
Response
Target cell detects signaling molecule
Signaling molecule binds to receptor protein
Cell surface
Inside cell
Fig. 11.6

8. Overview of Cell Signaling7
Transduction
Conversion of signal to a form that can bring about a cellular response
May be several steps with intermediaries: signal transduction pathway
relay molecules
Response
Fig. 11.6

9. Reception High specificity Receptor proteins Ligand On plasma membrane8
High specificity
Receptor proteins
On plasma membrane
G protein coupled receptors
Receptor tyrosine kinases
Ion channel receptors
Inside cell
Ligand
A molecule that binds specifically with another molecule

10. Transduction Signal Transduction Pathways9
Transduction
Signal Transduction Pathways
A mechanism linking a mechanical or chemical stimulus to a specific cellular response
Reception of signal by receptor protein on plasma membrane

11. Signal Transduction Pathways10
Phosphorylation activates a protein
Phosphate group is transferred from ATP (adenosine triphosphate) to the protein
Protein changes conformation
Relay molecules often protein kinases
Protein that transfers phosphate groups from ATP to another protein
Fig. 11.9

12. Signal Transduction Pathways11
Phosphorylation cascade
a series of different molecules in a pathway are phosphorylated in turn, and add phosphate group to next molecule in pathway
Dephosphorylation returns protein to inactive form
Protein phosphatases
enzymes that rapidly remove phosphate groups from a protein
Turns off / resets the pathway
Fig. 11.9

13. Response Occurs in nucleus or cytoplasm Response in nucleus12
Occurs in nucleus or cytoplasm
Response in nucleus
Often protein synthesis
Activates transcription factor to turn gene “on” (or off)
Start/stop transcription of RNA from DNA
Fig

14. Response Response in cytoplasm13
Response in cytoplasm
E.g., breakdown of glycogen into glucose
Fig

15. Signal Amplification 14
At each step in the cascade, the number of activated products is greater than the proceeding step
Proteins remain in activated form long enough to process many other molecules before becoming inactive
A few epinephine molecules leads to release of hundreds of millions of glucose molecules from glycogen
Fig

16. Transduction when using Intracellular Receptors15
Intracellular receptor proteins
Cytoplasm
Nucleus
Signal molecule must cross plasma membrane
Hydrophobic or small
E.g., steroids hormones, thyroid hormones

17. Transduction when using Intracellular Receptors16
Fig. 11.8
Signal molecule binds with receptor protein in cell
Becomes active
Receptor protein often a transcription factor, or activates a transcription factor
Start/stop transcription of RNA from DNA
Results in protein synthesis

18. Specificity of Cell Signaling17
Response of a cell to a signal depends on the type of proteins found in the target cell
Fig

19. Signal Transduction in Yeast18
How do yeast grow towards each other?
Read Fig Inquiry: How do signals induce directional cell growth in yeast. Focus on methodology.
Fig
1. Mating factor activates receptor
2. G protein binds GTP and becomes activated
3. Phosphoylation cascade activates Fus3, which moves to plasma membrane
4. Fus 3 phophorylates formin, activating it
Formin initiaes growth of microfiliments
Shmoo projections form
Fig. 11.2