1. Warm-Up Why do you communicate? How do you communicate?
How do you think cells communicate?
Do you think bacteria can communicate? Explain.

2. Warm-Up
Compare the structure & function of these receptor proteins: GPCR, tyrosine kinase and ligand-gated ion channels.
What is a second messenger? What are some examples of these molecules?
What are the possible responses to signal transduction in a cell?

3. Cell Communication
CHAPTER 11

4. Do bacteria communicate?
Bonnie Bassler on How Bacteria “Talk”

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. Cell Signaling Animal cells communicate by:
Direct contact (gap junctions)- passing between adjacent cells
Secreting local regulators— interactions between molecules protuding from surfaces.
Long distance (hormones)- Endocrine glands

7. Paracrine---secreting cells act on a nearby target cell by secreting molecules of regulation (growth factor)
Synaptic—a nerve cell releasing neurotransmitters into a synapse to stimulate a muscle or another nerve cell
Endocrine– specialized endocrine cells secrete hormones into body fluids

8. 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

9. Reception
A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell’s surface or (inside the cell).

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. 3Types of Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
Pg. 215
A cell surface receptor that binds with a G-Protein (an energy rich protein). Useful in the embryonic development and sensory receptions such as vision, taste, and smell. Malfunctions of G-Protein lead to bacterial infections.
G protein + GTP activates enzyme  cell response
Pg Receptors that have an enzymatic activity. Kinases catalyzes phosphate groups. Abnormal kinase receptors are associated with many kinds of cancer.
Activate multiple cellular responses at once
Pg Receptors that contains a region that can act as a “gate” for when the receptor changes shape. Ions such as “Na+ or Ca+2” are either blocked or allowed into the cell.
Regulate flow of specific ions
(Ca2+, Na+)

12. G-Protein-Coupled Receptor

13. Receptor Tyrosine Kinase

14. Ligand-Gated Ion Channel

15. 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

16. Transduction
The signaling molecule changes the receptor protein that will result in a specific cellular response.
Can be a single step or a series of steps called a signal transduction pathway

17. Response
The transduced signal triggers a specific cellular response. Signaling ensure the right cells get the right signal at the right time and in proper coordination with activities of other cells.

19. Second Messengers
small, nonprotein molecules/ions that can relay signal inside cell
Eg. cyclic AMP (cAMP), calcium ions (Ca2+), inositol triphosphate (IP3)

20. cAMP cAMP = cyclic adenosine monophosphate
GPCR  adenylyl cyclase (convert ATP  cAMP)  activate protein kinase A

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

22. An Example of Cell Communication

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

24. 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

25. Viagra Used as treatment for erectile dysfunction
Inhibits hydrolysis of cGMP  GMP
Prolongs signal to relax smooth muscle in artery walls; increase blood flow to penis

26. Viagra inhibits cGMP breakdown

27. 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)

28. 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”)

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