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Lecture 8

bio230Lecture 8 Text

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University of Toronto St. George
Jennifer Harris

BIO230H1 Lecture 8 Notes 887-891 Nitric Oxide Gas Signals by Directly Regulating the Activity of Specific Proteins Inside the Target cell  Cell to cell signaling  Signal molecule that activate intracellular  Nitric oxide and steroid hormones  Extracellular signal molecules and bind on the surface of the target cell  Nitric oxide (NO) which acts the signal molecule in both animal and plants  NO can relax smooth muscles  Autonomic nerves release acetylcholine  No affects the blood stream  Many types of nerve cells use NO more directly to signaling  NO synthase (NOS): NO is made by the deamination of amino acid arginine  NOS in endothelial: eNOS  NOS is found in the nerve and muscle: nNOS  Inductile (iNOS)  NO can readily cross the membrane  NO enzyme for the active site (guanylyl cyclase) can turn to GTP to GDP  Carbon monoxide uses it in a similar way Nuclear Receptors are Ligand-Modulated Gene Regulatory Proteins  Various small hydrophobic molecules  Signal molecules include steroid hormones, thyroid hormone, retinoids and vitamin D  Nuclear Receptor superfamily: Receptors are structurally related  Steroid hormones: sex hormone, vitamin D  Vitamin D: Calcium  There are nuclear receptors that respond  There are transcriptional response involve multiple steps  Primary response: protein products of these gene in turn activate other genes to produce a delayed: secondary response  Many types of cells by the nature of the signal molecule  Hydrophobic signal molecule and have receptors that bind to a lignad 667-671 (not panel 11-2) Ion Channels and the Electrical Properties of Membrane  Ion channels: protein channels that allow ions to cross  Ex. Na+, Ca2+ or Cl- Ion Channels are Ion-Selective and Fluctuate Between Open and Closed States  Ion selectivity: inorganic ions to pass and pores can be selective  Selectivity filter: limits the rate of passage  There can be different channels  Voltage gated, ligand gated and mechanically gated  There are K+ channels The Membrane Potential in Animal Cells Depends Mainly on K+ leak Channels and the K+ Gradient Across the Plasma Membrane  Membrane potential arises when there is a difference in electrical charge  There is a Na+-K+ pump help maintain balance  K+ leak channels help maintain the balance The Resting Potential Only Slowly When the Na+-K+ Pump  Ions can change with the resting potential  The membrane develops a positive and negative side 675-6
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