Ch. 11 Cell Communication

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.

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.Their work investigated how the animal hormone epinephrine stimulates breakdown of the storage polysaccharide glycogen in liver and skeletal muscle. The three stages of cell signaling are reception, transduction, and response

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 on intact cells.However, epinephrine did not activate the phosphorylase directly but could only act on intact cells. Therefore, there must be an intermediate step or steps occurring inside the cell.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.Also, the plasma membrane must be involved in transmitting the epinephrine signal. Sutherland’s discovery

The process must involve three stages. 1.In reception, a chemical signal binds to a cellular protein, typically at the cell’s surface. 2.In transduction, binding leads to a change in the receptor that triggers a series of changes along a signal-transduction pathway. 3.In response, the transduced signal triggers a specific cellular activity. Sutherland’s discovery: 3 stages

Stages of cell signaling: example Glycogen depolymerization by epinephrine 3 steps:Reception: target cell detectionTransduction: single-step or series of changesResponse: triggering of a specific cellular response

Signal-transduction pathway Definition: Signal on a cell’s surface is converted into a specific cellular response 1.Local signaling (short distance): Paracrine (growth factors – act on same or adjacent cells) Paracrine (growth factors – act on same or adjacent cells) Synaptic (neurotransmitters – transmit nerve impulse) Synaptic (neurotransmitters – transmit nerve impulse) 2.Long distance: endocrine hormones (travel through blood all over body)

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.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. 1.This may activate the receptor so that it can interact with other molecules. 2.For other receptors this leads to aggregation of receptors. A signal molecule binds to a receptor protein causing the protein to change shape

Signal transduction animations hill.com/olc/dl/120073/bio15.swf hill.com/olc/dl/120073/bio15.swf hill.com/olc/dl/120073/bio15.swf hill.com/olc/dl/120073/bio15.swf

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

Key common steps: Second messengers Non-protein signaling pathway Example: cyclic AMP (cAMP) Ex: Glycogen breakdown with epinephrine Enzyme: adenylyl cyclase G-protein-linked receptor in membrane (guanosine di- or tri- phosphate)

Cellular responses to signals 1.Cytoplasmic activity regulation 2.Cell metabolism regulation 3.Nuclear transcription regulation