Photoreception and Transduction Flashcards Preview

Anatomy and Physio Final > Photoreception and Transduction > Flashcards

Flashcards in Photoreception and Transduction Deck (72):
1

What is the visible spectrum?

400nm - 700nm

2

Why is the sky blue?

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

3

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

3 photons per cone per second
1 million photons/cone/second

4

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

larger
deeper in the RPE

5

In humans, there are ____ rods for every cone

20

6

True/False. More peripheral cones looks like rods

True

7

What role do cilia play in photoreceptors?

Support for the connection between the outer and inner segment layers

8

Visual transduction takes place in the _______

outer segment of photoreceptors

9

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

Ellipsoid and Myoid

10

What is the Ellipsoid part of a photoreceptor?

outer part of the inner segment. Contains Mitochondria

11

What is the Myoid part of a photoreceptor?

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

12

Where is the cell body of a photoreceptor located?

Outer nuclear layer (think nucleus = nuclear layer)

13

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

Out receptor fiber

14

What is the spherule?

the synaptic end of the rod and cone

15

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

rod - rounded
cone - pyrimadal

16

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

disks
infoldings

17

There are no rods in the _____

fovea

18

What is the peak sensitivity of a rod?

500 nm

19

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

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

20

What % of photoreceptors are cones?

3%

21

foveal cones are ______ than peripheral cones

foveal cones are smaller

22

Rod sensitivity to light is due to what?

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

23

What is the peak sensitivity of Long-wavelength cones?

560 nm

24

what is the peak sensitivity of medium-wavelength cones?

530 nm

25

what is the peak sensitivity of short-wavelength cones?

420 nm

26

what is the peak sensitivity of UV-sensitive cones?

355 - 440 nm. NOT IN HUMANS mothafucka

27

How are blue cones different from other cones?

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

28

All photopigments are forms of ______

rhodopsin

29

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

Melanopsin

30

What are the three photopsins in order of increasing wavelength?

Cyanolabe - blueish violet
Chlorolabe - green
Erthyrolabe - yellowish red

31

What make up photopigments?

Proteins (opsin) + Chromophore

32

What is chromophore derived from?

Vitamin A

33

How is the chromophore joined to the opsin?

Schiff base

34

Rhodopsin is how many amino acids long?

348

35

S-cone opsins are how many amino acids long?

346 - 350

36

L/M opsins are how many amino acids long?

364

37

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

the N - terminal

38

What is found at Position 296 on the photopigment chain?

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

39

What is found at Position 291 on the photopigment chain?

Binding pocket for chromophore

40

What is Positions 110 and 187 on the photopigment chain?

critical for folding

41

L and M cones are found on what gene?

X - chromosome

42

All mammalian photopigments have what type of chromophore?

11-cis-retinal

43

What is an opsin shift?

Any pigment that has a peak sensitivity different from 440 nm

44

In porphyropsin, the chromophore is the aldehyde of ______

Vitamin A2

45

In rhodopsin, the chromophore is the aldehyde of ______

Vitamin A1

46

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

T285A and Y277F

47

Where would you find porphyropsin?

Fresh water fish

48

What's the difference between rhodopsin and porphyropsin?

rhodopsin - shorter Vmax
Porphyropsin - longer Vmax

49

What happens in the light reaction?

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

50

What event triggers transduction?

the formation of metarhodopsin II

51

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

reversible by blue light

52

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

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

53

What happens 10 minutes after meta II is formed?

chromophore is released

54

What happens 20 minutes after meta II is formed?

rhodopsin is formed

55

What is "the fit" in a dark reaction?

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

56

What are the three peaks for Rhodopsin?

alpha peak - visible range
beta peak
gamma peak

57

What is the beta peak?

bond between opsin an chromophore. 350 nm

58

what is the gamma peak?

bond between tyrosin and tryptophan. not seen by humans

59

What is transduction?

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

60

what is photoreception?

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

61

what is the biochemical cascade?

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

62

what is the electronic spread?

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

63

what is synaptic deactivation?

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

64

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

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

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

1. Activated G protein binds with *PDE*
2. This molecule converts *cGMP* into GMP
3. cGMP concentration lowers, *ion channels* close

66

What causes the hyperpolarization during electronic spread?

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

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

2%

68

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

34 pA change for 600 ms or more

69

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

1/20th. Much shorter

70

Photocurrent in cones is ______ as opposed to _____ in rods

biphasic as opposed to monophasic

71

What is light adaptation controlled by?

Ca+ influx

72

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

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