Photopigments of Rods and Cones

Question 1

Rods and cones contain special photopigments each containing what?

Answer 1

A protein: opsin and a chromophore.

Question 2

What is a chromophore?

Answer 2

A light-sensitive molecule.

Question 3

What is the photopigment of rods?

Answer 3

rhodopsin

Question 4

What are the photopigment of cones?

Answer 4

color pigments or iodipsins or cone opsins.

Question 5

What is the opsin protein in rods called?

Answer 5

Scotopsin

Question 6

What is the opsin portion in cones called?

Answer 6

Photopsin

Question 7

What sets scotopsins and photopsin apart?

Answer 7

They have different amino acid composition and they absorb different wavelength of light.

Question 8

Chromorphore is the same or different in rods and cones?

Answer 8

They are the same.

Question 9

What is the chromophore composition?

Answer 9

an aldehyde of vitamin A (retinaldehyde)

Question 10

11-cis retinal isomer of retinal is what?

Answer 10

The chromophore

Question 11

What is rhodopsin?

Answer 11

Scotopsin plus 11-cis retinal

Question 12

What are the functions of the visual pigments?

Answer 12

They act as photoreceptors and they are required for vision.

Question 13

What do the visual pigments detect?

Answer 13

Detection of shape, depth, and color.

Question 14

The absorption of light energy by rhodopsin causes what?

Answer 14

a raid transformation fo 11-cis retinal to all trans retinal.

Question 15

What binds less avidly to opsin ?

Answer 15

Trans retinal

Question 16

What does all trans retinal isomer cause?

Answer 16

Conformational changes in scotopsin

Question 17

What activates the transducin ( a G-Protein)?

Answer 17

The trans retinal isomer becomes free and moves laterally in the plasma membrane and then activates it.

Question 18

What occurs during the regeneration of rhodopsin?

Answer 18

All trans retinal is converted to 11-cis retinal.

Question 19

How is all trans retinal converted to 11-cis retinal?

Answer 19

by retinal isomerase

Question 20

Regenerated 11 cis retinal automatically recombines with scotopsin to form what?

Answer 20

Rhodopsin.

Question 21

When rhodopsin is activated it is what?

Answer 21

Decomposing rhodopsin

Question 22

When rhodopsin is deactivated it is what?

Answer 22

regenerated rhodopsin

Question 23

Where is vitamin A present?

Answer 23

In the cytoplasm of the rods and cones as well as in retinal pigment epithelial cells.

Question 24

What does vitamin A convert to?

Answer 24

11-cis retinal as needed.

Question 25

What occurs to Vitamin A for storage?

Answer 25

excess retinal is converted to retinol (vit A)

Question 26

What is night blindness (nyctalopia)?

Answer 26

the inability to see in relatively low light.

Question 27

What is a major cause of night blindness?

Answer 27

Vitamin A deficiency

Question 28

What is vitamin A deficiency?

Answer 28

Less retinal is formed than needed

Question 29

At night or with low light the retinal levels are what?

Answer 29

inadequate for vision in a subject that has night blindness.

Question 30

The dark is referred to what type of state?

Answer 30

unexcited state.

Question 31

The unexcited state Na+ conductance into outer segment of rods is what?

Answer 31

Greater than that of a typical sensory cells.

Question 32

What does the cyclic guanosine monophosphate regulate?

Answer 32

The transmembrane conductance of sodium in photoreceptor cells.

Question 33

In the dark what occurs to the cytoplasmic levels of cGMP?

Answer 33

They increase

Question 34

What occurs when cGMP levels increase?

Answer 34

The cGMP regulated channels become activated and increase Na+ influx.

Question 35

The membrane potential in an unexcited state in a low light environment is what?

Answer 35

More positive

Question 36

The membrane potential of that in any other sensory cells in an unexcited state is what?

Answer 36

More negative.

Question 37

The excitation of rods by light results in what?

Answer 37

hyper polarization not depolarization

Question 38

excitation in other sensory receptors are usually caused by?

Answer 38

depolarization

Question 39

In bright light the activation of rhodopsin causes what?

Answer 39

stimulation of the G protein called transducin

Question 40

The activation of transducin leads to what?

Answer 40

The stimulation of phosphodiesterase

Question 41

What does phosphodiesterase do in Rod hyper polarization in light?

Answer 41

hydrolyzes cGMP to 5'GMP

Question 42

The activation of photopigments in cones is similar to what?

Answer 42

Rods

Question 43

What does the activation in cones require?

Answer 43

More photons for the same response in as rods.

Question 44

Cones are 30-300 fold less what then rods?

Answer 44

Less sensitive to light than rods.

Question 45

The extent in amplification in con excitation cascade is what?

Answer 45

much less than in rods.