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Human basic neuroscience > Biochemistry of the Visual System > Flashcards

Biochemistry of the Visual System Flashcards

1
Q

rods are responsible for what type of vision?

A

light vision

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2
Q

cones are responsible for what type of vision?

A

color detection

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3
Q

what is the opsin associated with rods?

A

rhodopsin

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4
Q

what are the opsins associated with cones?

A

red, green, and blue

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5
Q

what are the general characteristics of rods?

A

they have a high sensitivity but a low spatial resolution

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6
Q

what are the general characteristics of cones?

A

they have low sensitivity but high spatial resolution

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7
Q

which photoreceptor can respond to a single photon?

A

rods

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8
Q

what type of system is found in the disc membranes?

A

the GPCR system

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9
Q

what is the membrane spanning protein found in the GPCR system in the disc membranes?

A

opsin (rhodopsin)

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10
Q

what is the specific G protein found in the disc membranes?

A

transducin

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11
Q

what is found on the surface membrane of rods?

A

cGMP-gated Na+ channel, Na+/Ca2+-exchanger, and guanylate cyclase

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12
Q

what is the status of the cGMP-gated Na+ channel in dark conditions?

A

they are open and the cell is depolarized

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13
Q

what is the status of the cGMP-gated Na+ channel in light conditions?

A

Na+ channels are closed and the cell is hyperpolarized

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14
Q

what kind of neurotransmitter is released under dark conditions?

A

in the dark, a photoreceptor (rod/cone) cell will release glutamate, which inhibits (hyperpolarizes) the ON bipolar cells and excites (depolarizes) the OFF bipolar cells.

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15
Q

what is rhodopsin homologous to?

A

the beta-adrenergic receptor

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16
Q

what is found right in the middle of the membrane spanning region of rhodopsin?

A

lysine-296

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17
Q

What is the effector protein that is found on the disc membranes in rods?

A

phosphodiesterase

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18
Q

what does the lysine-296 covalently bind to?

A

its chromophore-11-cis-retinal

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19
Q

what is formed when the lysine-296 covalently binds to the 11-cis-retinal?

A

a schiff base

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20
Q

when we are talking about the light-activated rhodopsin and its chromophore retinal we are looking specifically at what?

A

at the pronated schiff base version of rhodopsin covalently bounded with retinal at the lysine 296

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21
Q

what happens when a photon reacts with retinal bound to rhodopsin?

A

there is a energetically induced isomaerization from 11-cis-retinal to all-trans retinal

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22
Q

what is the activated version of rhodopsin referred to as?

A

metarhodopsin II (Rh*)

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23
Q

what chromosome is the rod opsin protein coded on?

A

3

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24
Q

what chromosome is the blue opsin protein coded on?

A

7

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25
Q

what chromosome is are the red and green opsin proteins coded on?

A

X chromosome

26
Q

what is the absorption maxima of blue opsin protein?

A

420 nm

27
Q

what is the absorption maxima of green opsin protein?

A

530 nm

28
Q

what is the absorption maxima of red opsin protein?

A

> 560 nm

29
Q

What is the first step of the physical blockage mechanism of signal termination/ desensitization?

A

rhodopsin kinase will phosphorylate the C-terminus of Rh* at the threonine and serine residues

30
Q

what does phosphorylation of the threonine and serine residues at the C-terminus of the Rh* promote?

A

it promotes the binding of the protein Arrestin at the C-terminus of Rh*

31
Q

what does binding of the Arrestin protein cause?

A

inhibition of the rhodopsin interacting with its G protein transducin

32
Q

what does the innate GTPase activity of transducin cause?

A

rapid hydrolysis of GTP to GDP. This will cause the dissociation of the alpha-subunit from the PDE. Makes the PDE inactive once again and the alpha subunit will reassociate with the B- and Y- subunits

33
Q

what makes the cGMP PDE inactive?

A

the Y-subunit

34
Q

What triggers the activity of the guanylate cyclase?

A

low levels of intracellular Ca2+

35
Q

what is the action of the guanylate cyclase?

A

it will use GTP to reform the cGMP

36
Q

retinal is locally produced in the retina from what?

A

dietary vitamin a

37
Q

how else is vitamin a produced?

A

by B-carotene

38
Q

what happens when you have deficient levels of vitamin a?

A

you can get deficient levels of retinal, retinol, or retinoic acid

39
Q

what are the symptoms of vitamin A deficiencies?

A

night blindness, visual impairment, dry eyes, and bitot’s spots

40
Q

what are bitot’s spots?

A

a build up of keratin superficially in the conjunctiva; usually “foamy” in appearance

41
Q

what is golden rice fortified with?

A

beta-carotene

42
Q

once the 11-cis-retinal is transformed into all-trans-retinal, where is the all-trans-retinal shuttled to?

A

the retinal pigmented epithelium

43
Q

what transports the all-trans-retinal from the disc membrane into the cytoplasm?

A

ABC transporter

44
Q

what happens if you have a deficiency of the ABC transporter?

A

you will have a build up the all-trans-retinal in the disc membrane, which will affect the health of the photoreceptor cell itself

45
Q

what happens to the all-trans-retinal once it gets into the cytoplasm?

A

it is reduced to all-trans-retinol

46
Q

once the all-trans-retinol gets moved out of the photoreceptor cell, what is it bound to?

A

cellular retinoid binding protein (CRBP)

47
Q

where does the CRBP transport the all-trans-retinol to?

A

to LRAT

48
Q

what does LRAT do to the all-trans-retinol?

A

it esterifies it; so it will now be all-trans- retinyl ester

49
Q

where is the all-trans-retinyl ester transported to?

A

to RPE65

50
Q

what does RPE65 do to the all-trans- retinyl ester?

A

converts it to 11-cis-retinol

51
Q

what shuttles the 11-cis-retinol to it’s next spot?

A

a binding protein CRALBP

52
Q

where does the CRALBP take the 11-cis-retinol?

A

to 11cRDH

53
Q

what does 11cRDH do to the 11-cis-retinol?

A

it oxidizes it to 11-cis-retinal

54
Q

where is the 11-cis-retinal shuttled back to?

A

to the photoreceptor cell using iRBP

55
Q

in the RPE, what can you have deficiencies in?

A

LRAT and RPE65

56
Q

what does deficiencies in LRAT and RPE65 lead to?

A

retinitis pigmentosa

57
Q

the high flux of photons by light exposure can lead to what?

A

elevated levels of toxic retinal metabolites

58
Q

what are the classical presentation signs of retinitis pigmentosa?

A

decreased night vision and peripheral vision

59
Q

upon a retinal examination, what would you find in a patient with retinitis pigmentosa?

A

bony spicule formation in the RPE

60
Q

what does degeneration of the macula in the retina cause?

A

loss of central field vision

61
Q

what are mutations in the ABC4 gene known to cause?

A

macular degeneration

Human basic neuroscience (68 decks)

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