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Anatomy and Physio Final > Photoreception and Transduction > Flashcards

Photoreception and Transduction Flashcards

1
Q

What is the visible spectrum?

A

400nm - 700nm

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2
Q

Why is the sky blue?

A

Blue light is scattered more than any other color because it has the shortest wavelength of any color we can see

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3
Q

Cones start to respond to light around _____ photons/cone/second and can extend up to _____ photons/cone/second

A

3 photons per cone per second

1 million photons/cone/second

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4
Q

Anatomically, rods are ____ than cones are lie ____ in the RPE

A

larger

deeper in the RPE

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5
Q

In humans, there are ____ rods for every cone

A

20

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6
Q

True/False. More peripheral cones looks like rods

A

True

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7
Q

What role do cilia play in photoreceptors?

A

Support for the connection between the outer and inner segment layers

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8
Q

Visual transduction takes place in the _______

A

outer segment of photoreceptors

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9
Q

What are the two parts of the inner segment of visual cells?

A

Ellipsoid and Myoid

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10
Q

What is the Ellipsoid part of a photoreceptor?

A

outer part of the inner segment. Contains Mitochondria

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11
Q

What is the Myoid part of a photoreceptor?

A

inner part of the Inner segment part. Contains organelles and tubules

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12
Q

Where is the cell body of a photoreceptor located?

A

Outer nuclear layer (think nucleus = nuclear layer)

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13
Q

How is the cell body of a photoreceptor connected to the inner segment?

A

Out receptor fiber

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14
Q

What is the spherule?

A

the synaptic end of the rod and cone

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15
Q

In rods, the spherule is ______ while in cones, the spherule is ______

A

rod - rounded

cone - pyrimadal

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16
Q

a rod outer segment contains _____ while a cone outer segment contains _____

A

disks

infoldings

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17
Q

There are no rods in the _____

A

fovea

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18
Q

What is the peak sensitivity of a rod?

A

500 nm

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19
Q

True / False. Sensitivity of light in photoreceptors is due to pigment sensitivity

A

FUCK NO! Rod and Cones have the same pigment sensitivity.

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20
Q

What % of photoreceptors are cones?

A

3%

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21
Q

foveal cones are ______ than peripheral cones

A

foveal cones are smaller

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22
Q

Rod sensitivity to light is due to what?

A

CONVERGENCE of light information from multiple rods onto single retinal bipolar cells

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23
Q

What is the peak sensitivity of Long-wavelength cones?

A

560 nm

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24
Q

what is the peak sensitivity of medium-wavelength cones?

A

530 nm

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25
Q

what is the peak sensitivity of short-wavelength cones?

A

420 nm

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26
Q

what is the peak sensitivity of UV-sensitive cones?

A

355 - 440 nm. NOT IN HUMANS mothafucka

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27
Q

How are blue cones different from other cones?

A
  1. shape similar to rods
  2. mainly in parafoveal region
  3. amino acid sequence similar to rods
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28
Q

All photopigments are forms of ______

A

rhodopsin

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29
Q

What is the fourth opsin that is thought to play a role in the control of the circadian rhythm?

A

Melanopsin

30
Q

What are the three photopsins in order of increasing wavelength?

A

Cyanolabe - blueish violet
Chlorolabe - green
Erthyrolabe - yellowish red

31
Q

What make up photopigments?

A

Proteins (opsin) + Chromophore

32
Q

What is chromophore derived from?

A

Vitamin A

33
Q

How is the chromophore joined to the opsin?

A

Schiff base

34
Q

Rhodopsin is how many amino acids long?

A

348

35
Q

S-cone opsins are how many amino acids long?

A

346 - 350

36
Q

L/M opsins are how many amino acids long?

A

364

37
Q

The additional length of the L/M opsins can be found at what region of the protein?

A

the N - terminal

38
Q

What is found at Position 296 on the photopigment chain?

A

e- amino group of lysine residue which provides the link between opsin and chromophore

39
Q

What is found at Position 291 on the photopigment chain?

A

Binding pocket for chromophore

40
Q

What is Positions 110 and 187 on the photopigment chain?

A

critical for folding

41
Q

L and M cones are found on what gene?

A

X - chromosome

42
Q

All mammalian photopigments have what type of chromophore?

A

11-cis-retinal

43
Q

What is an opsin shift?

A

Any pigment that has a peak sensitivity different from 440 nm

44
Q

In porphyropsin, the chromophore is the aldehyde of ______

A

Vitamin A2

45
Q

In rhodopsin, the chromophore is the aldehyde of ______

A

Vitamin A1

46
Q

What spectral tuning sites account for the majority of rod and cone sensitivity changes?

A

T285A and Y277F

47
Q

Where would you find porphyropsin?

A

Fresh water fish

48
Q

What’s the difference between rhodopsin and porphyropsin?

A

rhodopsin - shorter Vmax

Porphyropsin - longer Vmax

49
Q

What happens in the light reaction?

A

Light causes 11-cis retinal (bent form) to change to all-trans retinal (straight form)

50
Q

What event triggers transduction?

A

the formation of metarhodopsin II

51
Q

The reactions that occur before the formation of meta II are ______ by ______

A

reversible by blue light

52
Q

Why is blue light the only way to reverse the light reaction?

A

it is the only color that has enough energy to cause the reformation of the bend of the molecule

53
Q

What happens 10 minutes after meta II is formed?

A

chromophore is released

54
Q

What happens 20 minutes after meta II is formed?

A

rhodopsin is formed

55
Q

What is “the fit” in a dark reaction?

A

Change in spectral peak with change in conformration of the chromophore and protein

56
Q

What are the three peaks for Rhodopsin?

A

alpha peak - visible range
beta peak
gamma peak

57
Q

What is the beta peak?

A

bond between opsin an chromophore. 350 nm

58
Q

what is the gamma peak?

A

bond between tyrosin and tryptophan. not seen by humans

59
Q

What is transduction?

A

the transformation of light into electrical and chemical signals that produce the perception of light

60
Q

what is photoreception?

A

photon absorbed by visual pigment that is lying on one of the discs in the outer segment

61
Q

what is the biochemical cascade?

A

in light, the pigment molecule is activated and the ion channels close

62
Q

what is the electronic spread?

A

after the ion channels close, there is a buildup of positive charge on the outside of the photoreceptor making it hyperpolarized

63
Q

what is synaptic deactivation?

A

the concentration of calcium decreases, leading to a decrease in the release of glutamate

64
Q

Explain how the G protein is activated by Rhodopsin:

  1. ______ runs into an inactive G molecule
  2. the _____ part sits on top of Rhodopsin
  3. ____ replaces GTP
  4. ______ separates from the G molecule
A
  1. Rhodopsin runs into an inactive G molecule
  2. the G alpha part sits on top of Rhodopsin
  3. GDP replaces GTP
  4. G alpha unit separates from the G molecule
65
Q

Explain how the G protein combines with cGPDE:

  1. Activated G protein binds with _____
  2. This molecule converts ____ into GMP
  3. cGMP concentration lowers, ____ close
A
  1. Activated G protein binds with PDE
  2. This molecule converts cGMP into GMP
  3. cGMP concentration lowers, ion channels close
66
Q

What causes the hyperpolarization during electronic spread?

A

K+ ions are moving out of the cell even after the channels close due to lower cGMP concentration. Produces a positive charge on the outside of the photoreceptor because Ca+ and Na+ no longer move in

67
Q

A single photon isomerization will close ion channels and cause a ___% reduction in the photocurrent

A

2%

68
Q

The rod photocurrent causes a ____ change in current and lasts ____ or more

A

34 pA change for 600 ms or more

69
Q

Photocurrent in cones is ____ the rod response and the duration is _____

A

1/20th. Much shorter

70
Q

Photocurrent in cones is ______ as opposed to _____ in rods

A

biphasic as opposed to monophasic

71
Q

What is light adaptation controlled by?

A

Ca+ influx

72
Q

cGMP is regulated by ____ because that molecule binds to _______, which synthesizes cGMP.

A

cGMP is regulated by Calcium because calcium binds to GCAP, which synthesizes cGMP.

Anatomy and Physio Final (9 decks)

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