Bio10 - Rhodopsin light Activated Rhodopsin Rhodopsin kinase Activated Rhodopsin(phosphorylated P Arrestin Activated Rhodopsin(phosphorylated P

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The visual system
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Ophthalmoscope
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Intracellular discs ->
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Pigmented Ep
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Pigment epithelium
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Blind spot- region where there Photoreceptors are NOT present
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Retina Rods – operate under dim illumination; are color blind Cones – operate under bright illumination Three cone types; mediate color perception Fovea – high resolution area Contains high density of cones, no rods Cone size increase and density falls off as we move away from the fovea Rod size increase and density increases and then falls off as we move away from the fovea Density is zero in the fovea No vision in the blind spot – filling in
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Phototransduction
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Baylor
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-30 mV -70 mV
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Ligand that binds to Na+ channels Does NOT bind to Na+ channels
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Light One rhodopsin molecule absorbs one photon 500 transducin molecules are excited 100,000 cyclic GMP molecules are hydrolyzed One million Na ions per second are prevented from entering the cell 500 phosphodiesterase molecules are excited 250 Na channels close
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Unformatted text preview: + Rhodopsin + light Activated Rhodopsin Rhodopsin kinase Activated Rhodopsin (phosphorylated) P Arrestin Activated Rhodopsin (phosphorylated) P arrestin Action of Rhodopsin is Terminated after light flash All-trans retinal Active site on opsin is exposed The active site activates transducin and changes rod membrane potential Active site Metabolic energy 11-cis retinal rhodopsin Retinal separates from opsin thereby bleaching rhodopsin Metabolic energy brings opsin back to its original form and attaches retinal to it. Light Absorption of light converts 11-cis retinal into all-trans retinal Pigment epithelium Phototransduction • Photoreceptors are hyperpolarized ( not depolarized ) in response to light • Second messenger G-protein coupled reaction • Massive amplification • Specialized mechanism for terminating the response • Responses in the photoreceptors and bipolar cells are graded (no action potentials)...
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This note was uploaded on 06/10/2011 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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Bio10 - Rhodopsin light Activated Rhodopsin Rhodopsin kinase Activated Rhodopsin(phosphorylated P Arrestin Activated Rhodopsin(phosphorylated P

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