1. Signal Transduction
Cell Communication

2. Membrane Proteins

3. Cellular Communication
Cell Junctions: Interconnect adjacent cells
Anchoring junctions (desmosomes)
Abundant in tissues with high stress forces (Cardiac muscles)
Tight junctions
Forms leak-proof sheet (Epithelial cells)
Gap junctions & Plasmodesmata
Direct cytoplasmic connections
Extracellular matrix: dense mat of biomolecules
Adhesion proteins link cells to EM
Neurotransmitters: typically fast responses
Hormones: long-range, often sustained, systemic actions

5. Initial Signals Chemical Electromagnetic Pressure Temperature
Cations
Anions
Electrical gradient
Magnetic force field
Pressure
Temperature
Another Cell
Extracellular Matrix
Energy

7. Mechanisms of Cell Signaling
Signal molecule or physical factor from cell environment
Internal or External environment
Signal is “sensed” by target cell via Receptors
Plasma membrane
Cytoplasm
Organelle
Nuclear membrane /Nucleoplasm
Binding of ligand
Specificity
Agonist vs. Antagonist
Initiate Signal Transduction Pathway

9. Variables of Signaling Systems
Distance
Neighboring cells
Organismic
Endurance of signal
Seconds to hours to years
Target cell(s)
One or many
Specificity
Full molecule or merely a hapten /molecular structure
Feedback mechanisms
Feed-forward vs. Negative feedback

11. Calcium as 2nd Messenger

12. Role of Cholesterol
“Good” cholesterol = high-density lipoproteins (HDL)
>56 mg/ dL blood  60%% less Alzheimer’s cases than < 38% mg/ dL blood
Cholesterol is major component of cell membranes
25% of our total cholesterol is found in brain
Cholesterol is essential to forming connections between nerve cells
Allows creation & retention of memories
Glial cells supply neurons with cholesterol
Improves rate of nerve signal transmission
Allows neuronal connections
Lipid rafts composed of cholesterol & receptor proteins
Floating through plasma membrane prevents deactivation of protein
Statins interfere with cholesterol synthesis
May negatively affect memory in some patients