Ch. 11 Cell Communication

1. Ch. 11 Cell Communication

2. Signal transduction • The process by which a signal on a cell’s surface is converted into a specific cellular response • involves several steps in a signal-transduction pathway.

3. The three stages of cell signaling are reception, transduction, and response The origins of our understanding of cell signaling were pioneered by E.W. Sutherland and colleagues. • Their work investigated how the animal hormone epinephrine stimulates breakdown of the storage polysaccharide glycogen in liver and skeletal muscle.

4. Sutherland’s discovery Sutherland’s research team discovered that epinephrine activated a cytosolic enzyme, glycogen phosphorylase. • However, epinephrine did not activate the phosphorylase directly but could only act onintact cells. • Therefore, there must be an intermediate step or steps occurring inside the cell. • Also, the plasma membrane must be involved in transmitting the epinephrine signal.

5. Sutherland’s discovery: 3 stages The process must involve three stages. • In reception, a chemical signal binds to a cellular protein, typically at the cell’s surface. • In transduction, binding leads to a change in the receptor that triggers a series of changes along a signal-transduction pathway. • In response, the transduced signal triggers a specific cellular activity.

6. Stages of cell signaling: example Glycogen depolymerization by epinephrine 3 steps: •Reception: target cell detection •Transduction: single-step or series of changes •Response: triggering of a specific cellular response

7. Signal-transduction pathwayDefinition: Signal on a cell’s surface is converted into a specific cellular response Local signaling (short distance): Paracrine (growth factors – act on same or adjacent cells) Synaptic (neurotransmitters – transmit nerve impulse) Long distance: endocrine hormones (travel through blood all over body)

8. A signal molecule binds to a receptor protein causing the protein to change shape A cell targeted by a particular chemical signal has a receptor protein that recognizes the signal molecule. • Recognition occurs when the signal binds to a specific site on the receptor because it is complementary in shape. When ligands (small molecules that bind specifically to a larger molecule) attach to the receptor protein, the receptor undergoes a change in shape. • This may activate the receptor so that it can interact with other molecules. • For other receptors this leads to aggregation of receptors.

9. Signal transduction animations http://highered.mcgraw-hill.com/olc/dl/120073/bio15.swf http://highered.mcgraw-hill.com/olc/dl/120073/bio15.swf

10. Key common steps: Protein signaling by phosphorylation Protein activity regulation Adding phosphate from ATP to a protein (activates proteins) Enzyme: protein kinases (1% of all our genes) Example: cell reproduction

11. Key common steps: Second messengers Non-protein signaling pathway Example: cyclic AMP (cAMP) Ex: Glycogen breakdown with epinephrine Enzyme: adenylylcyclase G-protein-linked receptor in membrane (guanosinedi- or tri- phosphate)

12. Cellular responses to signals Cytoplasmic activity regulation Cell metabolism regulation Nuclear transcription regulation