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30 Cards in this Set
- Front
- Back
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What are the steps to the regeneration of rhodopsin? |
1. trans-retinal reduced to trans-retinol 2. trans-retinol shutted to RPE 3. 11-cis-retinal regenerated in RPE 4. 11-cis-retinal shuttled to rod cell 5. Rhodopsin generated |
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What does rhodopsin stimulate? |
1. Transducin |
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Where is rhodopsin most highly concentrated? |
1. Disk membrane |
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What binds the aldehyde moiety of 11-cis retinal to rhodopsin? |
1. Schiff's base to lysine residue 296 |
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What effect does absorption of a photon have on 11-cis retinal? |
1. all trans retinal |
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What is the sequence of conformational changes that occur in rhodopsin upon the formation of all trans retinal? |
1. Bathorhodopsin---- lumirhodopsin--- metarodopsin I |
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What is the active rhodopsin that interacts with transducin? |
1. Metarhodopsin II |
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What is the function of rhodopsin kinase? |
1. Add up to 8 phosphates to R* |
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What is the affinity of phosphorylated R* for transducin? |
1. Decreased |
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What does R*P bind? |
1. Arrestin |
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What is the function of arrestin? |
1. Blocks transducing binding site 2. R*-arrestin cannot activate transducin |
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What is the result of the conformational change to R*? |
1. H2O has access to retinal, resulting in hydrolysis of all trans retinal |
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What form of transducin exists in the dark? |
1. GaBy-- bound to GDP |
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What happens when R* binds transducin? |
1. Replacement of GDP with GTP 2. a subunit separates and binds to PDE6 3. GTP is hydrolyzed |
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What is the slowest step in rod vision? What regulates this step? |
1. GTP hydrolysis 2. Regulated by GTPase accelerating proteins (GAPs) |
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What is the structure of PDE6? |
1. aB2y 2. aB=active |
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What is the effect of Ga-GTP binding on the activity of PDE6? |
1. Increases 1000x |
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How do CNG ion channels function? |
1. AS cGMP decr4eases, CNG channels close 2. Flow of Na and Ca into cell decreases--- hyperpolarization--- decrease in glutamate release |
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What is the role of gunaylyl cyclase in recovery? |
1. Increased when Ca is low 2. Ca binding proteins 3. As Ca decreases, GC begins to increase to regenerate cGMP |
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What form of retinal will opsin bind? |
1. 11-cis retinal |
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What reduces all trans retinal to all trans retinol in the retinoid cycle? |
1. Retinol DH |
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What happens to trans retinol in the RPE? |
1. Esterified by lecithin:retinol acyltransferase to form retinyl esters 2. Can be stored |
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For what is trans retinyl ester a substrate? |
1. RPE65 isomerase--- produces 11-cis retinyl ester |
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For what are cones responsible? |
1. Color vision |
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What are the three types of cones? What makes them different? |
1. Red 2. Green 3. Blue 4. Different due to differences in amino acids in and near retinal binding pocket |
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Where are the genes for rhodopsin, blue pigment, and red and green pigments? |
1. Rhodopsin-- chromosome 3 2. Blue-- chromosome 7 3. Red and green-- X chromosome |
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What is the MCC of retinitis pigmentosa? |
1. Progressive rod-cone dystrophy 2. Mutations in proteins of the phototransduction system |
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What is LCA? |
1. Severe early onset form of retinal degeneration 2. Mutations in: retinal specific guanylyl cyclase and RPE65 |
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What is bradyopsia? What causes it? |
1. Inability to rapidly shut off the phototransduction cascade after stimulation by a photon 2. Caused by mutations in RGS9 or R9AP--- accelerate the GTP hydrolysis step |
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What are the proposed mechanisms for diabetic retinopathy? |
1. Impaired autoregulation of retinal blood flow 2. Sorbitol accumulation in retinal cells 3. Advanced AGEs |
