Lecture 22: Phototransduction

Question 1

What opsin is found in rods?

Answer 1

Rhodopsin

Question 2

Rods have ____ sensitivity and ____ spatial resolution.

Answer 2

Rods have high sensitivity and low spatial resolution.

Question 3

What opsins are found in cones?

Answer 3

Three opsins: red, green, and blue

Question 4

Cones have ____ sensitivity and ____ spatial resolution.

Answer 4

Cones have low sensitivity and high spatial resolution.

Question 5

What portion of the photoreceptor is connected to the bipolar cell?

Answer 5

Inner Segment

Question 6

What is included in the GPCR system of the outer segment of photoreceptor cells?

Answer 6

Opsins
Transducin
cGMP phosphodiesterase

Question 7

What is included on the surface membrane of the outer segment of photoreceptor cells?

Answer 7

cGMP gated Sodium Channels
Sodium/Calcium exchanger
Guanylate cyclase

Question 8

What happens to cGMP gated Sodium Channels in the dark?

Answer 8

They are open and cells are depolarized

Question 9

What happens to cGMP gated Sodium Channels in the light?

Answer 9

They are closed and cells are hyperpolarized

Question 10

What AA is found in the center of the 7TM receptor?

Answer 10

Lysine-296

Question 11

What is the difference between the Schiff base and protonated Schiff base of Retinal bound rhodopsin?

Answer 11

Protonated Schiff base absorbs >440 nm

-active player for signal transduction

Question 12

What happens when photon when light contacts 11-cis retinal?

Answer 12

11-trans-retinal, kicking off the entire signal transduction pathway

Question 13

What is the inheritance pattern of colorblindness?

Answer 13

X-linked

Question 14

Gt activation by light activates what?

Answer 14

cGMP Phosphodiesterase

Question 15

What happens when there is low cGMP?

Answer 15

Hyperpolarization of visual cells –> visual signal transduction

Question 16

What can cause signal termination?

Answer 16

1. Rhodopsin Kinase
2. Rapid hydrolysis of ATP to ADP
3. Elevated levels of cGMP

Question 17

What are consequences of Vitamin A deficiency?

Answer 17

Night blindness
Xerophthalmia
Keratinization of epithelium
Dry, scaly skin
AMD
Blindness in children
Cornea issues
Increased likelihood of dying from infections

Question 18

What are bitot spots?

Answer 18

Build up of keratin in conjunctiva (looks foamy)

Question 19

What is xerophthalmia

Answer 19

Abnormal dryness of conjunctiva and cornea of the eye with inflammation and ridge formation

Question 20

What are the two cellular systems of the retinoid cycle?

Answer 20

Photoreceptors
Pigmented Epithelium (RPE)

Question 21

What are two important proteins in the retinoid cycle?

Answer 21

LRAT

RPE65

Question 22

What is macular degeneration?

Answer 22

Degeneration of RPE and retina that can result in vision loss