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Topic 5 Signalling.odt

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Topic 5 Cell SignallingCell Communicationresponsible for the controlled growth and development of an animal as well as the integrated activities of its tissues and organsOne way communicate is via intercellular chemical messengers One cell the controlling cell synthesizes a molecule to act as a signalling molecule to affect the activity of another cell the target cell The two cells are not in contact For ex In response to stress cells of adrenal gland secrete epinephrine that acts on various target cells Epinephrine acts by activating enzyme glycogen phosphorylase which catalyzes the production of glucose from glycogen Enzyme activation did not involve epinephrine but did require an unknown cellular substanceHormone was called the first messenger unknown cellular substance second messengerIn brief a controlling cell releases a signal molecule that causes a response of target cells Target cells process the signal in the following 3 steps1Receptionbinding of the signal molecule with a specific receptor of the target cellReceptors are specific to the signal moleculesignal molecules are often peptides steroid but can be many other molecules such as aminesMembrane receptors are normally on the cell surface embedded in the plasma membrane but can be located within the cell where the signal molecules passes freely through the plasma membraneSteroid hormones such as testosterone have receptors within the cell Receptors at the cell surface usually involve rapid short lived events membrane receptorsInternal receptors often act directly on the genome nuclear receptors2Transductionchanging the signal into a form necessary to cause the cellular responseoften involves a cascade of reactionssignalling cascade3Responsetransduced signal causes specific cellular responseCell communication has three components 1 the extracellular signal molecules are released by controlling cells 2 the surface receptors on target cells that receive the signals and 3 the internal response pathways that are triggeredHormones and Neurotransmitters surface receptors bind 2 major types of signal molecules hormones and neurotransmittersreleased by control cells enter fluid including blood circulation in animalsHormones are molecules usually peptides or steroids that are resleased by gland cells nerve cells organ cells Neurotransmitters are released by neurons include small peptides amino acids or other
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