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Visual System (Rhodopsin (Located in disc membranes of rods, Intradisc N…
Visual System
Rhodopsin
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Intradisc N-terminus, cytoplasmic C-terminus
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Opsin protein + 11-cis-retinal, schiff-base covalent linkage
All-trans-retinol (vit. A) -> All-trans-retinal -> 11-cis-retinal
(retinol dehydrogenase, retinal isomerase)
MoA (Activation)
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Transucin (G protein) activated and alpha subunit activates a cGMP phosphodiestrease. This lowers cGMP and closes cGMP gated Na channels on the ROD CELL MEMBRANE
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Overview
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Requirements: substance to absorb light (chromophore) + conformational change of chromophore upon photon abs.
Membrane ass. receptors, enzymes ion channels, and intraceullar regulatory proteins and enzymes
Photoreceptors
Rods can respond to single photon, 10 required for visual flash
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MoA (Inactivation)
- Arrestin leads to desensitization
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- Alpha subunit of transducin has inbuilt GTPase activity
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Colour vision
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3 genes: R+G (X-chromosome), B (autosomal)
AD, AR*, Sex-linked, allied diseases
Dominant (10%): chromosome 3 rhodopsin point mutation
chromosome 6: peripherin mutation (rod structural protein)