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)
Secreting local regulators (growth factors, neurotransmitters)
Long distance (hormones)

7. Cell-to-Cell Communications
Cell junctions directly connect the cytoplasm of adjacent cells
Ex: cardiac cells for rhythmicity; plamodesmata between plant cells
Surface receptors can give/send information
Ex: specific immune response
VIDEO
Plasma membranes
Plasmodesmata
between plant cells
Gap junctions
between animal cells

8. diffuses across synapse
Local Signaling
VIDEO
Adjacent cells are signaled.
Chemical messengers released
Ex: Neurotransmitters via neurons
(a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.
(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.
Local regulator
diffuses through
extracellular fluid
Target cell
Secretory
vesicle
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across synapse
is stimulated
Local signaling

9. Long Distance Signaling
Use of hormones
Both plants and animals
use hormones (e.g. Insulin)
Can affect many cells in
Other parts of the body
Protein or Steroid types
Hormone travels
in bloodstream
to target cells
(c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood Hormones may reach virtually all body cells.
Long-distance signaling
Blood
vessel
Target
cell
Endocrine cell
Figure 11.4 C

10. How Does it Work? Signal Transduction Pathways
Convert signals on a cell’s surface into cellular responses
Are similar in microbes and mammals, suggesting an early origin

11. 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

12. Reception

13. Transduction

14. Response

15. 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

16. Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels

17. G-Protein-Coupled Receptor

18. G-Protein-Coupled Receptor
Very Common
Results in a single pathway response

19. Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
7 transmembrane segments in membrane
G protein + GTP activates enzyme  cell response

20. Receptor Tyrosine Kinase
Multiple Pathway Response

21. Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
Attaches (P) to tyrosine
Activate multiple cellular responses at once

22. Ligand-Gated Ion Channel
When ligand binds, channel can open or close
Ex: neurotransmitters bind as ligands for Na+ ion channels

23. Plasma Membrane Receptors
G-Protein Coupled Receptor (GPCR)
Tyrosine Kinase
Ligand-Gated Ion Channels
Signal on receptor changes shape
Regulate flow of specific ions
(Ca2+, Na+)

24. 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

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

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

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

29. An Example of Cell Communication

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

31. 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

32. 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

33. Viagra inhibits cGMP breakdown

34. 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)

35. 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”)

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