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19 Cards in this Set
- Front
- Back
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dichromate
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captures/differentiates 2 wavelengths of light
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where does one find trichromates?
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higher mammals and apes, etc..
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wavelenths of trichromates?
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blue (420 nm), green (535 nm), red (570 nm)
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rhodopsin
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chromoprotein found in rod-type cells in retina
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what is rhodopsin used for?
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used in adaptation to dim light, 30 minutes to recover to photobleaching
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wavelength(s) for rhodopsin
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peaks around 500 nm
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what is retinal?
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vitamin A aldehyde, key chromophore involved in transduction of light
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components of rhodopsin
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11-cis retinal and opsin -> photopigment
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rhodopsin light mechanism?
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retinal absorbs photon
promotes to excited state -> all-trans retinal (photoisomerization) no longer fits to opsin -> triggers g-protein pathway |
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how many photons to trigger nerve impulse?
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minimum 5 photons
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chromophore
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part of molecule responsible for color
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photoisomerization
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changes chromophore from one isomer to another
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what causes range of absorption peaks
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protonation of schiff base (fixed shift)
cone pigments have cl- binding site -> longer wavelengths |
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how is the chromophore attached to the opsin?
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helix 7 forms covalent Schiff base attachment with lysine to retinal (protonated, exists as salt bridge, together with negative charge of acidic group from glutamate on helix III)
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g-pritein mechanism with retinal
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binding of alpha subunit to effector enzyme (not beta-gamma)
alpha subunit coupled to phosphodiesterase channels gated by secondary messenger cGMP in vertebrates light closes channels permeable to cations |
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outer segment of rod/cone
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sensory membrane elaborated from a modified cillium, containing visual pigment and enzymes/channels required for transudction
rods contain disks, cones have invaginations ~1100 rod disks, or 750 cone invaginations |
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inner segment of rod/cone
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metabolic part of cell, highly organized, mitochondria (ellipsoid body)
plasma membrane adjacent to mitochondria contains high concentration of Na/K atpase ER and nucleus below the ellipsoid body |
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synaptic terminal in rod/cone cells
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spherule in rods
pedicle for cones |
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photoreceptor cell type
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secondary receptor cells, lacking voltage gated Na+ channels
do not generate Na+ dependent action potentials signals -> 2nd order horizontal/bipolar cells |
