1. Cell Communication

2. Signal Transduction Pathways
Signal recognized by receptor molecule, then converted to response
ligand: the signaling molecule
receptor protein: the molecule to which the receptor binds
may be on the plasma membrane or within the cell

3. Signaling
Junctions directly connect cytoplasms (including plasmodesmata)
Direct cell-cell contact/recognition
Cells can identify each other by cell surface markers.
major histocompatibility complex (MHC) proteins are used by cells to distinguish “self” from “non-self”

4. Local Signaling Messenger molecules secreted
Growth factors example of paracrine signaling
Synaptic signaling uses neurotransmitters

5. Long-distance Signaling
Hormones released into blood
Can move through cells/air, too
Electrical signals travel through nerve cells

6. 1. Reception Chemical signal binds to receptor
Receptors can turn on/off genes
Ex: ion-channel receptors

7. Receptor Types 3 subclasses of membrane receptors:
1. Channel linked receptors – ion channel that opens in response to a ligand
2. G protein-coupled receptor – a G-protein (bound to GTP) assists in transmitting the signal
3. Enzymatic receptors (receptor tyrosine kinases) – receptor is an enzyme that is activated by the ligand

8. 2. Transduction Receptor changes shape Kinases phosphorylate proteins
“phosphorylation cascade”
Phosphatases dephosphorylate

9. Example: Cyclic AMP “second messenger”
Enzyme converts ATP to cAMP in response to signal
cAMP activates kinase, which causes cellular responses

10. 3. Response Regulate activity/synthesis of enzymes
Transcription factors
Signal “amplified” after each step

11. Cell Suicide Apoptosis- programmed cell death
Discards of old and/or damaged cells
Uses multiple signaling pathways