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Unformatted text preview: Lecture 15 Lecture 15: Integration and Regulation of Metabolism Chapter 12: Biosignaling- signal transduction: conversion of information into a chemical change- Specificity : achieved by precise molecular complementarity between the signal and receptor molecules - Amplification : by enzyme cascades results when enzyme associated with a signal receptor is activated; catalyzes the activation of many molecules of second enzyme; each activates many third enzymes, etc.- Desensitization : sensitivity of receptor is subject to modification- when a signal is present continuously, the receptor becomes less sensitive; when stimulus falls below certain threshold, the system is sensitive again- Integration : ability of the system to receive multiple signals and produce a unified response - General features of signal transduction: activated receptor interacts with cellular machinery produces second signal or change in activity of cellular protein metabolic activity of target cell undergoes a change transduction event ends and cell returns to prestimulus state- 6 basic signaling mechanisms: o Gated ion channels : open and close in response to binding of chemical ligands or changes in transmembrane potential; simplest: acetylcholine receptor ion channel o Receptor enzymes : transverse membrane; when one off these receptors is activated by its extracellular ligand, it catalyzes the production of an intracellular second messenger; e. g. insulin receptor o Serpentine receptors : indirectly activate through G-proteins enzymes that generate intracellular second messengers; e.g. -adrenergic receptor system detecting epinephrine o Steroid receptors : when bound to ligand will alter the rate at which specific genes are transcribed o Receptors that lack enzymatic activity : attract and activate cytoplasmic enzymes that act on downstream proteins by directly converting them to gene-regulating enzymes or activating a cascade of enzymes that finally activates a gene regulator o Adhesion receptors : interact with macromolecular components of extracellular matrix and convey to the cytoskeletal system instruction on cell migration o All 6 types require activation of protein kinases: enzymes that transfer a phosphoryl group from ATP to a protein side chain 12.3 Receptor Enzymes- have ligand-binding domain on the extracellular surface of plama membrane and enzyme active site on the cytosolic side 1 of 9 Lecture 15- Receptor enzyme is a protein kinase that phsophorylates Tyr residue in specific target proteins- Insulin receptor: passes signal from plasma membrane receptor to insulin-...
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This note was uploaded on 02/25/2010 for the course BIOL 2800 taught by Professor Salomon during the Spring '09 term at Brown.
- Spring '09