Biochemistry of Vision Flashcards
- Layers of Retina proximal to distal
- types of cells
- RPE
- Photoreceptor outer segments
- Outer nuclear layer
- Outer plexiform layer
- Inner nuclear layer
- Inner plexiform layer
- Ganglion cell layer
- optic nerve layer
*Light travels through 8–>1 then gets converted into signals going back towards layer 8
Processing of visual signals- general idea from cell type to cell type
-ganglion cells are what part of optic nerve?
Rod Cells:
part specizlized for photoreception, how many discs?
-whats in the disks?
outer segment is for photoreception, 1000 discs, disc contain densely packed rhodopsin
Rods vs cones
- sensitivity vs spatial resolution
- photoreceptor molecules
Rhodopsin:
- protein part
- chromophore part, derivative of?
opsin is protein, 11 cis-retinal is chromophore derivative of vitamin a
Rhodopsin structure vs Beta 2
Rhodopsin:
- which lysine located in 7th TM protein and what is it bound to?
- what forms schiff base
- protonation
Optical properties of retinal-lysine conformers:
- free 11-cis retinal light absorption maximum
- unprotonated schiff base light absorption
- protonated shiff base
- rhodopsin light
- suggests?
What does photon do to rhodopsin?
Rhodopsin changes into metarhodopsin II
Visual signal transduction pathway
*receptor activation reduces concentration of cGMP instead of increasing it
*hyperpolarization inhibits signaling
• Incident photon absorbed by Rhodopsin in a photoreceptor cell. • Interacts with the retinal which isomerizes from 11-cis to all-trans configuration • Causes conformational change in rhodopsin to become Metarhodopsin or R*. • R* interacts with G protein transducin, catalyzing its activation to G* by the
release of bound GDP in exchange for cytoplasmic GTP • G* disassociates from its β and γ subunits. • G* activates phosphodiesterase (PDE) which hydrolyzes cGMP. • Lowered cGMP levels close the cGMP-gated sodium channels. • Closure of the sodium channels causes hyperpolarization of the cell and neuronal
signaling • At each step of the process, there is significant amplification.
Amplification of signal
Signal Termination Steps
• Light-activated rhodopsin blocked from activating transducin • Rhodopsin kinase phosphorylates COOH terminus of R* aka
metarhodopsin II at Thr and Ser allowing binding by Arrestin
and preventing interaction with Transducin • Transducin has intrinsic GTPase activity. Hydrolyses GTP to
GDP causes dissociation of transducin from PDE and re-
association with βγ subunits • Guanylate cyclase synthesizes cGMP from GTP • Elevated cGMP levels re-open cGMP-gated ion channels
Role of Ca+2
- dark vs light
- calcium influx balanced by what exchanger
Role of Ca+2 general
-how does calcium govern rate at which system is restored
Signal to brain:
- rods and cones release what in dark, what does light do
- glutamate role on bipolar cells
- what do horizontal and amacrine cells do?
**don’t have to know really
Cone-specific visual pigments
varieties absorb what nm of light
Color blindness
- what leads to it?
- people cant distinguish what colors
cant distinguish red vs green
Retinoid Cycle:
- In rod Cell: role of iRBP
- in RPE: what does LRAT do in ER
- RPE65 role RDH role, exported how?
Photoreceptor renewal:
- what part vulnerable to damage?
- do rods and cones divide?
- what happens to tips?
Disk Shedding:
-circadian manner of rod vs cone shedding
Retinitis Pigmentosa:
- mutations in what?
- affect disc how?
- characterized by?
Food sources of Vitamin A
Disorders associated w/ vitamin A
- xeropthalmia?
- bitot’s spots?
- skin/ gi symptoms
Night Blindness:
-glaucoma, cataracts, diabetes, retinitis pigmentosa?
