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Lecture%2031-1

Lecture%2031-1 - Lecture 31 Animal Hormones and sex...

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Lecture 31 26/11/2007 11:28:00 Animal Hormones and sex determination  2 broad classes of hormones o lipid soluble (non-polar) steroids testosterone cholesterols dissolve in lipids cell membrane can pass through them easily receptors can be inside the cell because they don’t  need to be on the surface o water soluble polar Cannot diffuse easily through membrane Requires plasma membrane bound receptors Once bound, receptors can undergo  conformational changes to carry out function Steroid Hormones bind to intracellular receptors Binding of the hormone activates the receptor which then binds DNA and  directly alters gene transcription levels Water Soluble hormones bind to membrane receptors Insulin binds to a surface receptor o Results in the dimerization of 2 receptors
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2 insulin molecules bnd 2 receptors and then the receptors bind  to one another this dimerization activates a kinase domain which corss  phosphorylates the receptors as well as allows for  phosphorylation of other proteins inside the cell Some surface receptors act as channels and can open up once bound to an  extra-cellular ligand Protein kinase cascade amplifies a response to receptor binding o One protein is activated by the activated receptor which can then  activate another protein and another and another which propagates the  signal exponentially o HGF (Human Growth Factor) Binds to surface receptor (RTK – receptor tyrosine kinase) Receptor activates Ras Ras is usually bound to a GDP and is inactive Once active Ras replaces GDP with a GTP This is carried out using a Ras GEF ( G TP  E xchange  F actor) Ras then activates Raf Raf activates MEK MEK activates MAPK MAPK acts as TF o Why all these steps?
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