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Ch. 15 - Cell Communication - Part 1 A summary of the chapter and lecture notes on cell communication. Includes illustrations and graphics from the textbook.

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York University
BIOL 2021
Julie Clark

BIOL 2021 April 9 2009CHAPTER 15 Cell Communication I Communication between cells is mediated mainly by extracellular signal molecules Figure 151 a simple intracellular signalling pathway activated by an extracellular signal molecule The signal molecule usually binds to a receptor protein that is embedded in the plasma membrane of the target cell and activates one or more intracellular signalling pathways mediated by a series of signalling proteins Finally one or more of the intracellular signalling proteins alters the activity of effector proteins and thereby the behaviour of the cellExtracellular signal moleculesCan include proteins small peptides amino acids nucleotides steroids etc Signal molecules can be released into the extracellular space by exocytosis from the signalling cell or by diffusion through the signalling cells plasma membrane Others are displayed on the external surface of the cell and remain attached to it providing a signal to other cells only when they make contact transmembrane proteins ReceptorBinds the signal molecule and then initiates a response in the target cellUsually transmembrane proteins on the target cell surface but can also be inside the cell where signal molecule must enter the cell and bind to them Figure 153a The binding of extracellular signal molecules to either the cellsurface or intracellular receptors A Most signal molecules are hydrophilic and are therefore unable to cross the target cells plasma membrane directly instead they bind to cellsurface receptors which in turn generate signals inside the target cell Figure 153b Some small signal molecules by contrast diffuse across the plasma membrane and bind to receptor proteins inside the target cell either in the cytosol or in the nucleus as shown above Many of these small signal molecules are hydrophobic and nearly insoluble in aqueous solutions they are therefore transported in the bloodstream and other extracellular fluids bound to carrier proteins from which they dissociate before entering the target cellContact dependant signalling signal molecules remain bound to the surface of the signalling cell and influence only cells that contact it 153aImmune responses developmentLarge distancesParacrine signalling 154b short range cellcell communication via secreted signal molecules that act on neighbouring cells Act locally signal molecules do not diffuse far because they are taken up by neighbouring target cells destroyed by extracellular enzymes or immobilized by the extracellular matrix Cell that produce signals that they themselves respond to are called autocrine signallingEndocrine cellsSecrete signal molecules called hormones into the blood stream which carries them to target cells all over the bodySignalling over long distances
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