13 - Chapter 13. SIGNAL TRANSDUCTION SYSTEMS For AS 100...

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Chapter 13. SIGNAL TRANSDUCTION SYSTEMS For AS 100 students (2007) – this material is largely beyond the scope of the treatment in class – please do not struggle with it, so concentrate on the first part – Overview. This chapter will be expanded to include several figures before it reaches its final form. A. Overview Cells in the tissues and organs of animals function cooperatively. That is, the activities of a given cell are influenced by contact with neighboring cells and by the nature of their attachment to extracellular connective elements. At a higher level, cells may be targets for the actions of growth factors and hormones that ultimately reach the cell via the surrounding interstitial fluid. Most of these external influences are first recognized by receptors in the plasmalemma yet they usually bring about reactions deep within the interior of the cell. To do so requires that events at the plasmalemma be functionally coupled to intracellular response systems. The mechanisms involved are broadly called signal transduction systems . The first of these to become really understood involved hormones that bind to plasmalemmal receptors and result in increased intracellular concentrations of the compound 3'5'-cAMP, with the latter then mediating the ultimate action of the hormone in controlling intracellular reactions. The hormone was viewed as being the primary messenger and 3'5'-cAMP was called the second messenger . cAMP- mediated signal transductions will be described in detail, later in the text. A more readily grasped example for the reader at this time is the situation where a signaling molecule (say, a hormone), binds to a plasmalemmal receptor and in so doing opens adjacent Ca 2+ channels. Flowing down a very large concentration gradient ([Ca 2+ ] o ~ 10,000-fold > than [Ca 2+ ] i ), the influx of Ca 2+ causes a transient increase in [Ca 2+ ] i and this increase triggers some Ca 2+ - responsive reaction within the cell. Several examples of this system will be noted in later chapters. A wide array of signal transduction
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This note was uploaded on 03/23/2009 for the course ANSCI 1110 taught by Professor Brucecurrie during the Fall '08 term at Cornell University (Engineering School).

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13 - Chapter 13. SIGNAL TRANSDUCTION SYSTEMS For AS 100...

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