L26 - Monday,November29,2010...

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Monday, November 29, 2010 Cell Communication: Signal Transduction Reading: Chapter 16, pages 537 - 558  Objectives In  metazoans  (multicellular animals), communication between cells is critical for  regulating:  o nerve impulse transmission o growth o physiological responses This communication involves signals.  Signal transduction  is the conversion of a  signal from one form to another.  During signal transduction, chemical messengers called  ligands  activate specific  receptors A simple example is provided by  steroid receptors o Steroids are hydrophobic cholesterol derivatives, and can pass directly  from the bloodstream into the cytosol. o Steroid receptors are intracellular . o The  glucocorticoid receptor  is normally present in the cytosol, complexed  with an inhibitor protein that masks its nuclear localization signal. Binding  of the hormone  cortisol  to this receptor releases the inhibitory subunit,  allowing the protein to translocate into the nucleus and activate  transcription. o A given steroid hormone can induce different responses in different cell  types. GENERALIZATIONS:  o 1) For a given messenger molecule, the signal transduction mechanisms  are very similar in different cell types. But each cell type has a specific  downstream response to that signal. o 2) For related messenger molecules, the signal transduction mechanisms  are very similar, but the specific responses differ.
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o 3) Basic signal transduction mechanisms have been evolutionarily 
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L26 - Monday,November29,2010...

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