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U8- Cell Communication SUMMARY.docx

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University of Waterloo
BIOL 130
Heidi Engelhardt

U8- CELL COMMUNICATION SUMMARY Endocrine/Paracrine/Neural: fig 16-3  Endocrine: Public; hormones produced in endocrine glands are secreted into the bloodstream and are distributed widely thru out the body  Paracrine: Less public; are released by cells into the extracellular fluid in their neighbourhood  Neural: Long range but private (telephone); transmitted along axons to remote target cells Receptor protein, target cell, signal transduction:  Receptor Protein: activated by only one type of signal; without the appropriate receptor, a cell will not respond to the signal  Signalling pathways: signal molecule is synthesized and released by signalling cell  signal molecule travels to target cell  signal binds to receptor protein on/in target cell (transduction)  changes in protein activity (activation. Inactivation); changes in gene expression  changes in cell shape, movement, metabolism, secretion…  Target cell: The same signal can cause different responses depending on the target cell (signal= acetyl choline (fig 16-5) o Acetylcholine binds to similar receptor proteins on heart muscle cells and salvary glands but it evokes different responses in each cell type Fast vs Slow Responses: A cell’s response can be fast or slow  Fig 16-7  Slow responses: Certain types of cell responses (such as, increased cell growth/division) involve changes in gene expression and reequire production of new proteins  Fast responses: do not involve changes in gene expression (such as, secretion, metabolism) Intracellular vs cell-surface receptors: Extracellular signal molecules bind either to cell surface receptors or to intracellular enzymes or receptors fig 16-8  Cell-surface receptors: Large extracellular molecules bind to cell-surface receptors, which generate one more signalling molecule inside the target cell  Intracellular receptors: Small extracellular signal molecules diffuse cross the target cell’s plasma membrane and activate enzymes directly or bind to intracellular receptors in either the cytosol or nucleus Small hydrophobic signal molecules typically enter the cell and regulate gene transcription fig 16-9 Mechanism of action, nuclear receptor family of transcription factors:  Mechanism of Action: Steroid Hormone Mechanism of action o Steroids are evolutionarily related  their receptors are members of nuclear receptor family of transcription factors (fig 16-10) o The steroid hormone cortisol acts by activating a transcription regulator Most signals bind to receptors on plasma membrane  fig 16-12 (many extracellular signals act thru cell-surface receptors to change the behaviour of the cell Cell-surface receptors:  Second Messengers: Small (non-protein) molecules that relay signals from cell surface receptors to target molecules within cell; involved in intracellular signalling “cascade” (fig 16-13)  Molecular Switches: Intracellular signal molecules act as molecular switches; can switch from being active to inactive when active (proteins can turn on other proteins o o (1) Signaling by protein phosphorylation: protein kinase activates switch (adds phosphate to switch); protein phosphatase deactivates switch (takes phosphate off again dephosphorylation) o (2) signalling by GTP-binding protein: GTP-binding signalling protein is induced to activate protein (by exhanging its bound GDP for GTP); hydrolysis of bound GTP deactivates switch  Phosphorylation, kinases / phosphatases, phosphorylation cascades: o Phosphorylation is used to regulate proteins o Turning a signal off (deactivaton) is just as important as turning it on (activation)  Each activation step in a cascade needs to be deactivated  Protein activity (regulated by phosphorylation) depends on balance between kinase and phosphatase activity o Many proteins regulated by phosphorylaton are kinases  phosphorylation cascades o Phosphorylation of proteins is NOT random  OH groups of serine and threonine residues are phoshporylated in a particular sequence  Phosphorylation Cascade: One protein kinase phosphorylates the next protein kinase and so on, transmitting the signal onward GTP-binding proteins (G-proteins):  Switch from active to inactive state (depends on if or if not they are bound to GTP or GDP  Once bound to GTP, they
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