11 Signal Transduction

11 Signal Transduction - B iochemis ry E duca ion...

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Unformatted text preview: B iochemis ry E duca ion Department of iochemistry & Molecular iology University of New Mexico BIOC 423 Int oducto y Biochemist y Overview of signal transduction OBJECTIVES To outline the basic concepts of signal transduction. To understand how cells use signals to communicate and be able to describe three different modes of transmitting that signal across membranes To focus on a few of the major signal transduction molecules used in the regulation of cellular metabolism. Extracellular signals Intracellular signals insulin cAMP glucagon cGMP generic steroid hormone diacylglycerol inositol triphosphate calcium To integrate concepts of membrane structure, receptors and signal transduction. OUTLINE Why signal transduction is necessary G-proteins adenylate cyclase system phoshoinositol system toxins (i.e., cholera toxin) that can affect G-protein systems Receptor tyrosine kinases Human growth factor (insulin-like) Steroid hormone signaling LECTURE General biochemistry Obviously the membrane presents a major barrier to moving information from outside of the cell to inside the cell. If the signal molecule is hydrophobic, it is only slightly soluble in the extracellular fluid and generally needs some form of carrier molecule. Once the lipid soluble signaling molecule enters the lipid bilayer it is very stable and there is a major energy barrier encountered when attempting to move the molecule into the cytoplasm. Consequently, the signal remains stuck in the membrane unless there are components in the cytoplasm that will remove the signal from the membrane. On the other hand, if the extracellular signaling molecule was water soluble we have the opposite problem. That is, the energy necessary to put the water soluble molecule into the interior of the membrane is extremely high and again the signal remains stuck, but this time outside of the membrane. To address both of the problems we will need to use both specific receptors and carrier molecules to transmit a signal across a membrane to its intended site of action. Functional properties of transducers In general, all signaling systems must: be specific (only specific signaling molecules fit the receptor) be able to amplify the external signal integrate information from a variety of sources turn themselves off when appropriate. Cells use four basic mechanisms to transmit signals: gated ion channels, G- protein-linked receptors (also called serpentine receptors), receptor enzymes (receptor tyrosine kinases), and steroid hormone receptors. Gated ion channels allow the movement of ions across membranes and in some respects are more like transport systems than signal transduction systems....
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11 Signal Transduction - B iochemis ry E duca ion...

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