Biochemistry Of Vision

Question 1

____ is the tough elastic outer layer of CT that wraps around to the anterior to become the cornea.

_____ is darkly pigmented tissue and provides blood and absorbs light to prevent internal reflection. The anterior part becomes the ____ and ____.

_____ is their innermost layer containing photoreceptor cells

Answer 1

Sclera

Choroid

Ciliary body and iris

Retina

Question 2

Visual field is the highest in the ____ because contains highest concentration of retinal cones

Answer 2

Fovea

Question 3

Visual signals are process through photoreceptors -> _____ -> ganglion cells.

What are four fx of ganglion cells?

Answer 3

Interneurons

Output cells of retina

Axons form optic N

Project to the brain

Info is transmitted by AP

Question 4

Disc membranes are stacked in outer membrane of photoreceptor cells; they contain photoreceptor _____.

____ is the main signal transduction pathway for vision. It contains rhodopsin, iodopsin, transduction, phosphodiesterase (cGMP->GMP)

Structural protein?

Answer 4

Proteins

GPCR

Peripherin

Question 5

The surface membrane of photoreceptor cells have cGMP gated Na channels, Na/Ca exchanger, and ____.

It also contains ancillary proteins of _____ that blocks the interaction of rhodopsin with transducin and ____ that does phosphorylation and is the first step in signal termination pathway.

Answer 5

Guanylate cyclase

Beta-arrestin

Rhodopsin kinase

Question 6

Rods have ____.

Cones have ____.

Answer 6

Rhodopsin: high sensitivity and low spatial resolution (detect light from dark at night)

Opsin: low sensitivity and high spatial resolution (color)

Question 7

In the dark (no photon input), cGMP gated Na channel open and the rods are ____. This depolarization causes rods to release the neurotransmitter ____, which inhibits optic nerve bipolar cells.

In the light, Na channels are closed and the rods are _____. Photons activate rhodopsin which stops the glutamate release causing signal transduction (relieves the inhibition of the optic N bipolar cells)

Answer 7

Depolarized

Glutamate

Hyperpolarized

Question 8

Rhodopsin is a _____ receptor.

Retinal is derived from ____ and forms a _____ with amine of lysine.

Retinal bound to rhodopsin is a ____ schiff base, therefore absorbs at a high wavelength.

Retinal undergoes a photon-induced isomerization. When a cis-retinal absorbs light, it becomes a ____. This starts the _____.

Answer 8

Beta adrenergic

Vitamin A

Schiff base

Protonated

Trans-retinal

Signal transduction pathway

Question 9

Light activates rhodopsin -> rhodopsin activates G protein _____, by changing GDP -> GTP.

GTP can now interact with PDE changing cGMP -> 5-GMP

Lower concentration of cGMP causes ____ of visual cells -> signal transduction.

Answer 9

Transducin

Hyperpolarization

Question 10

Signal transduction:

Photon interacts with the cis-retinal in _____ -> retinal isomerizes to trans-retinal rhodopsin -> rhodopsin interacts with _____ (G protein) -> G protein interacts with phosphodiesterase (cGMP-> GMP) -> Na channels close -> hyperporlarization of rods -> stops release of glutamate -> relieves inhibition

_____ converts GTP -> cGMP. Controls signal transduction because supplies cGMP.

What is the secondary messenger?

Answer 10

Rhodopsin

Transducin

Guanylate cyclase

cGMP

Question 11

Guanylate cyclase is activated by low ____ and inhibited by high levels.

In light, Ca influx through cGMP channel stops, but continues to export Ca, dropping Ca levels; this stimulates ____, restoring cGMP levels, and re-opening cGMP channels

Answer 11

Ca

Guanylate cyclase

Question 12

How is the signal terminated?

Answer 12

Light-activated rhodopsin is blocked from activating transducin by rhodopsin kinase, which phosphorylates rhodopsin and allows arrestin to bind, preventing interaction with transducin

Hydrolysis of ATP -> ADP

Elevated cGMP levels

Question 13

Trans-retinal is recycled to ____ using photoreceptors and RPE.

Dysfunction of RPE65 or LRAT lead to _____.

Answer 13

Chic-retinal

Retinal pigmentosa

Question 14

Trans-retinal in photoreceptor cell (rod) is reduced to trans-retinol (vitamin A) and exported to RPE by ____.

Trans-retinol is esterified by _____. Then converted to cis-retinol by _____.

Oxidized to cis-retinal and exported back to ____ by iRBP.

Answer 14

iRBP

Lecithin retinol acyl transferase (LRAT)

RPE65

Rod cell

Question 15

Cone red and green opsin proteins are found on the ____ chromosome.

Answer 15

X (x-linked recessive colorblindness)

Question 16

Deficiency of ____ from beta-carotene is the most nutritional disorder with respect to the cornea leading to ____.

Excess causes ____.

Infants exposed to ____ in womb can have birth defects like cleft palates and heart abnormalities.

Answer 16

Vitamin A

Bitot spots: build-up of keratin in conjunctiva (foamy)

Night blindness, xerosis, keratomalacia, growth impediment, failure of wounds to heal, dry skin, follicular hyperkeratosis, alopecia, bronchitis, pneumonia

Liver toxicity

Isotretinoin

Question 17

_____ is the degeneration of RPE and retina. What does it cause?

Mutation in ____ causes this disease and related disorders associated with severe loss in vision.

Answer 17

Macular degeneration

Loss of central field vision, poor night vision

ABCA4: works in clearance of trans-retinal derivatives from photoreceptors (allows retinal cycle)

Question 18

_____ prevent oxidative, UV damage to eye.

Answer 18

Macular carotenoids (xanthophylls): from kale