1. Curious Question
What is a second messenger? What are some examples of these molecules?
What are the possible responses to signal transduction in a cell?

2. Cell Communication
CHAPTER 11

3. What you should know:
The 3 stages of cell communication: reception, transduction, and response.
How a cell signal is amplified by a phosphorylation cascade.
How a cell response in the nucleus turns on genes while in the cytoplasm it activates enzymes.
What apoptosis means and why it is important to normal functioning of multicellular organisms.

4. Do bacteria communicate?

5. Video Questions:
Why are scientists studying how bacteria (and not just human cells) communicate?
What is quorum sensing?
Describe how Vibrio fischeri use quorum sensing in squid.
According to Bonnie Bassler (Princeton University), what are scientists hoping to use as the next class of antibiotics?

6. 3 Stages of Cell Signaling:
Reception: Detection of a signal molecule (ligand) coming from outside the cell
Transduction: Convert signal to a form that can bring about a cellular response
Response: Cellular response to the signal molecule

7. Reception

8. Transduction

9. Response

10. 1. Reception
Binding between signal molecule (ligand) + receptor is highly specific.
Types of Receptors:
Plasma membrane receptor
water-soluble ligands
Intracellular receptors (cytoplasm, nucleus)
hydrophobic or small ligands
Eg. testosterone or nitric oxide (NO)
Ligand binds to receptor protein  protein changes SHAPE  initiates transduction signal

11. G-Protein-Coupled Receptor

12. G-Protein-Coupled Receptor

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

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

16. Signal Transduction Pathway Problems/Defects:
Examples:
Diabetes
Cholera
Autoimmune disease
Cancer
Neurotoxins, poisons, pesticides
Drugs (anesthetics, antihistamines, blood pressure meds)

17. Cholera
Toxin modifies G-protein involved in regulating salt & water secretion
G protein stuck in active form  intestinal cells secrete salts, water
Infected person develops profuse diarrhea and could die from loss of water and salts
Disease acquired by drinking contaminated water (w/human feces)
Bacteria (Vibrio cholerae) colonizes lining of small intestine and produces toxin

18. Apoptosis = cell suicide
Cell is dismantled and digested
Triggered by signals that activate cascade of “suicide” proteins (caspase)
Why?
Protect neighboring cells from damage
Animal development & maintenance
May be involved in some diseases (Parkinson’s, Alzheimer’s)

19. Apoptosis of a human white blood cell
Figure Apoptosis of human white blood cells
Left: Normal WBC
Right: WBC undergoing apoptosis – shrinking and forming lobes (“blebs”)

20. Effect of apoptosis during paw development in the mouse
Figure Effect of apoptosis during paw development in the mouse