30: Visual System Biochem Flashcards

1
Q

How many rods vs cones do we have

A

Rods: 100 million
Cones: 7 million

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2
Q

What does rod convergence allow?

A

Rods can operate in dim light

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3
Q

Inner segment of rod and cone structure

A

Contains glycogen, mitos, and polyribosomes for biosynthetic activity

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4
Q

What is rhodopsin homologous to?

A

B-adrenergic receptors

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5
Q

7TM helices

A

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

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6
Q

Activation of rhodopsin: structural change that occurs

A

11-cis-retinal -> 11-trans retinal

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7
Q

Blue iodopsin vs red and green chromosome location

A

Blue: chrom 7

Red and green: chrom X

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8
Q

Disc membranes in photoreceptors

A

Vesicles stacked in outer membrane inside photoreceptor, contains opsins

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9
Q

Four notable proteins contained in disc membranes + their function

A
  1. Opsin: light detection
  2. Transducin: G protein
  3. CGMP phosphodiesterase: cGMP -> GMP
  4. Peripherin: structural
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10
Q

Three proteins on the surface of photoreceptor cells

A
  1. cGMP-gated NA channel
  2. Na/Ca exchanger
  3. Guanylate cyclase
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11
Q

What does guanylate cyclase convert?

A

GTP -> cGMP + PPi

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12
Q

Two desensitization proteins in photoreceptor cells

A

B-arrestin, rhodopsin kinase

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13
Q

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

A

The rate by which the visual system is restored

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14
Q

Main idea of signal termination in the visual signal transduction pathway

A

Activated rhodopsin is blocked from activating transducin

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15
Q

Recommended daily amount of vitamin A

A

3000 ug

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16
Q

Dietary sources of vitamin A

A

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

17
Q

Leading cause of preventable blindness in children

A

Vitamin A deficiency

18
Q

What can vitamin A deficiency cause?

A
  1. Increased chance of dying from infections
  2. Night blindness
  3. Keratinization of epithelium
  4. AMD
  5. Xerphthalmia
  6. Bitot’s spots
19
Q

Xerophthalmia

A

Dry eye syndrome

20
Q

Bitot’s spots

A

Keratin debris in conjunctiva

21
Q

Additional presentation of vitamin A deficiency

A

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

22
Q

Two things caused by excess vitamin A

A

Liver toxicity, joint pain

23
Q

Infants exposed to accutane (isoretinoin)

A

Cleft palate, heart abnormalities

24
Q

Golden rice

A

1st genetically biofortified food, fortified with B-carotene

25
What can mutations in each step of the retinoid cycle cause?
Visual impairment and blindness
26
What do CRBP and CRALBP stand for?
CRBP: cellular retinoid binding protein CRALBP: cellular retinaldehyde binding protein
27
What does LRAT stand for?
Lecithin retinol acyl transferase
28
Visual loss in retinitis pigmentosa vs macular degeneration
Retinitis: decreased night vision and peripheral vision Macular: loss of central field of vision
29
What causes retinitis pigmentosa? Biochemically
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
30
Two proteins where dysfunction can cause retinitis pigmentosa
LRAT or RPE65
31
Risk factors for macular degeneration
Advanced age (over 70), Hx smoking, obesity, Caucasian, dietary factors (low zinc/omega-3/antioxidants or high fat)
32
A mutation in what protein can cause macular degeneration?
ABCA4