1. Cell Signaling Lecture 25 BSCI 420/421 Oct 30/31, ’02
The 4 Laws of Ecology:
“All things are interconnected.
Everything goes somewhere.
There’s no such thing as a free lunch.
Nature bats last.”
-Earnest Callenbach
A. General principles of Cell Signaling
B. Signaling thru cell surface receptors

2. Cell to cell signaling allows organisms to coordinate the activity
of a wide variety of different cell types.
General principles of cell to cell signaling.
Cells can communicate via signal molecules in 4 different ways:
Differ in distance over which they act.
Closest: e.g. Boss & Sevenless. E.g. Inductive dev. signals

3. E.g. neurotransmitters E.g. Insulin

4. Receptors for signal
Molecules can be either:
Cell surface
Signal mols are water soluble
E.g. peptide hormones
Induce cytoplasmic signal
cascade Or
Intracellular
Signal molecules are
hydrophobic e.g.steroids
Carriers in bloodstream

5. A simple signaling pathway or cascade induced by binding
To a cell surface receptor
Fig.15-1

6. Signal molecules that bind to intracell receptors,
and hence genes. All small & hydrophobic
Fig 15-12

7. Nuclear receptors
The DNA-binding domains
Contain multiple Zinc fingers

8. An animal cell depends on multiple extracellular signals

9. B. Signaling thru Cell Surface Receptors
3 Classes of Cell Surface Receptors
e.g Ach
receptors
e.g. epine-
phrine rec.

10. Types of surface receptors, cont.
e.g. Growth factor receptors

11. Too much stimulation can be a problem.
Cells need to be able to respond to changes in signal
over a wide range of conc
Target cells can become desensitized in 5 diff ways:

12. G-protein-linked receptors
The largest and most widespread family of cell surface receptors, found in all eukaryotes.
7- pass transmembrane proteins

13. Associate with a trimeric G Protein (GTPase)

14. Activated
Receptor acts
As a GNEF.
The alpha subunit
Exchanges GTP
For GDP
The other 2 s-units
Dissociate from
Alpha, and both
Diffuse away in an
Active state

15. Activation of
target protein
e.g. adenylyl
Cyclase
Hydrolysis
Of GTP
Formation of
The inactive
trimer