30: Visual System Biochem

Question 1

How many rods vs cones do we have

Answer 1

Rods: 100 million
Cones: 7 million

Question 2

What does rod convergence allow?

Answer 2

Rods can operate in dim light

Question 3

Inner segment of rod and cone structure

Answer 3

Contains glycogen, mitos, and polyribosomes for biosynthetic activity

Question 4

What is rhodopsin homologous to?

Answer 4

B-adrenergic receptors

Question 5

7TM helices

Answer 5

Make up 1/3 of all drug targets; humans make 800+ types of them

Question 6

Activation of rhodopsin: structural change that occurs

Answer 6

11-cis-retinal -> 11-trans retinal

Question 7

Blue iodopsin vs red and green chromosome location

Answer 7

Blue: chrom 7

Red and green: chrom X

Question 8

Disc membranes in photoreceptors

Answer 8

Vesicles stacked in outer membrane inside photoreceptor, contains opsins

Question 9

Four notable proteins contained in disc membranes + their function

Answer 9

1. Opsin: light detection
2. Transducin: G protein
3. CGMP phosphodiesterase: cGMP -> GMP
4. Peripherin: structural

Question 10

Three proteins on the surface of photoreceptor cells

Answer 10

1. cGMP-gated NA channel
2. Na/Ca exchanger
3. Guanylate cyclase

Question 11

What does guanylate cyclase convert?

Answer 11

GTP -> cGMP + PPi

Question 12

Two desensitization proteins in photoreceptor cells

Answer 12

B-arrestin, rhodopsin kinase

Question 13

Because Ca controls rate of cGMP synthesis, what does it govern

Answer 13

The rate by which the visual system is restored

Question 14

Main idea of signal termination in the visual signal transduction pathway

Answer 14

Activated rhodopsin is blocked from activating transducin

Question 15

Recommended daily amount of vitamin A

Answer 15

3000 ug

Question 16

Dietary sources of vitamin A

Answer 16

Carrots, leafy greens, sweet potatoes, squash, broccoli, animal products

Question 17

Leading cause of preventable blindness in children

Answer 17

Vitamin A deficiency

Question 18

What can vitamin A deficiency cause?

Answer 18

1. Increased chance of dying from infections
2. Night blindness
3. Keratinization of epithelium
4. AMD
5. Xerphthalmia
6. Bitot’s spots

Question 19

Xerophthalmia

Answer 19

Dry eye syndrome

Question 20

Bitot’s spots

Answer 20

Keratin debris in conjunctiva

Question 21

Additional presentation of vitamin A deficiency

Answer 21

Growth impairment, failure of wounds to heal, dry skin, alopecia, lung conditions (bronchitis, PNA)

Question 22

Two things caused by excess vitamin A

Answer 22

Liver toxicity, joint pain

Question 23

Infants exposed to accutane (isoretinoin)

Answer 23

Cleft palate, heart abnormalities

Question 24

Golden rice

Answer 24

1st genetically biofortified food, fortified with B-carotene

Question 25

What can mutations in each step of the retinoid cycle cause?

Answer 25

Visual impairment and blindness

Question 26

What do CRBP and CRALBP stand for?

Answer 26

CRBP: cellular retinoid binding protein
CRALBP: cellular retinaldehyde binding protein

Question 27

What does LRAT stand for?

Answer 27

Lecithin retinol acyl transferase

Question 28

Visual loss in retinitis pigmentosa vs macular degeneration

Answer 28

Retinitis: decreased night vision and peripheral vision
Macular: loss of central field of vision

Question 29

What causes retinitis pigmentosa? Biochemically

Answer 29

High light exposure -> increased toxic retinal metabolites that accumulate over time -> Loss of rod cells progressively, eventual loss of cones, bony spicules form in RPE

Question 30

Two proteins where dysfunction can cause retinitis pigmentosa

Answer 30

LRAT or RPE65

Question 31

Risk factors for macular degeneration

Answer 31

Advanced age (over 70), Hx smoking, obesity, Caucasian, dietary factors (low zinc/omega-3/antioxidants or high fat)

Question 32

A mutation in what protein can cause macular degeneration?

Answer 32

ABCA4