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Neuroendocrine > Biochemistry of the Visual System > Flashcards

Biochemistry of the Visual System Flashcards

1
Q

What are the types of photoreceptor cells?

A

Rods and cones

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2
Q

What do rods respond to?

A

Light detection

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3
Q

What do cones respond to?

A

Color detection

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4
Q

What receptor protein are rods associated with?

A

Rhodopsin

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5
Q

What receptor protein are cones associated with?

A

3 different opsins - red, green, blue

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6
Q

Between rods and cones, which has a high sensitivity but low resolution?

A

Rods

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7
Q

Between rods and cones, which has a low sensitivity but high resolution?

A

Cones

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8
Q

Why do cones have a low sensitivity but high resolution?

A

A single cone associates with a single bipolar cell

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9
Q

Why do rods have a high sensitivity but low resolution?

A

Many rods converge upon a single bipolar cell

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10
Q

Describe the organization or rods and cones

A

Synaptic ending, axon, nucleus, inner segment, outer segment that includes discs

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11
Q

Disc membranes in the outer segment include a GPCR system that initiates the pathway, what is in that system?

A

Opsin receptor protein, Transducin G protein, and cGMP Phosphodiesterase

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12
Q

Describe what happens when light enters the disc membrane of the outer segment of a rod

A
  • Light activates the rhodopsin receptor protein which activates the Transducin G protein
  • Transducin binds a GTP and the alpha subunit and GTP dissociate
  • Activated alpha subunit and GTP activate the phosphodiesterase
  • Phosphodiesterase takes cGMP to GMP, thus reducing the concentration of cGMP
  • This causes the Na/Ca channels to close and the cell is hyperpolarized and releases less glutamate
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13
Q

What is necessary to open the na/ca channel on the outer segment membrane?

A

cGMP, which is why the channels are closed when light is present and actively leading to its decrease

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14
Q

What will recreate cGMP leading to the cells depolarization and thus more release of glutamate?

A

Guanylate cyclase (GC)

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15
Q

Light leads to?

A

Hyperpolarization and thus less release of glutamate

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16
Q

Darkness leads to?

A

Depolarization and more release of glutamate

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17
Q

What forms a covalent link (schiff base) with 11-Retinal?

A

Lysine 296

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18
Q

Photo-activated lysine in the 7TM is ____

A

Pronated! It can now absorb light’s wavelength

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19
Q

What creates Retinal?

A

Vitamin A

20
Q

When light is added to 11-cis-retinal what results?

A

11-trans-retinal conformational change

21
Q

What opsin receptor proteins on cones are X chromosome inherited?

A

Red and green

22
Q

What wavelength is blue light?

A

420 nm

23
Q

What wavelength is red light?

A

560 nm

24
Q

What wavelength is green light?

A

530 nm

25
Q

Red/Green color blindness is inherited in what way and primarily affects what gender?

A

X-linked recessive, so carrier females often produce affected male sons

26
Q

What are 3 ways to terminate the signal that light started?

A

Rhodopsin Kinase, Innate GTPase activity of Transducin, and Guanylate cyclase

27
Q

Rhodopsin kinase phosphorylates C-terminus and results in what?

A

Arrestin binds and does not allow Metarhodopsin to interact with Transducin

28
Q

GTPase activity of transducin causes what?

A

Alpha subunit to inactivate and dissociate from phosphodiesterase

29
Q

Guanylate cyclase synthesizes cGMP from GTP and causes what?

A

Na channels to open and depolarize the cell

30
Q

What deficiency most commonly affects the eye/cornea?

A

Vitamin A/beta carotene

31
Q

Abnormal dryness of conjunctiva and cornea of eye

A

Xeropthalmia

32
Q

What are some things that vitamin A deficiency can cause?

A

Xeropthalmia, night blindness, visual impairment, Bitot’s spots, failure of wounds to heal

33
Q

Infants exposed to _____ in womb may be born with birth defects such as cleft palates and heart abnormalties

A

Accutane/Isotretinoin

34
Q

Vitamin A produces?

A

Retinal in the retina

35
Q

Vitamin A deficiencies are most common in developing nations, what food was fortified with beta carotene to try and prevent that?

A

Golden rice

36
Q

What is the purpose of the retinoid cycle?

A

Regenerate 11-cis-retinal

37
Q

Mutations in the retinoid cycle can cause?

A

Blindness

38
Q

Where does the retinoid cycle take place?

A

In the rod cells/photoreceptor cells and the Retinal Pigmented Epithelium (RPE)

39
Q

In a rod cell, what transports all-trans-retinal to the cytoplasm to prevent buildup?

A

ABC transporter

40
Q

Mutations in ABC transporter can cause?

A

Macular Degeneration

41
Q

Macular Degeneration

A

Loss of central field of vision due to buildup of all-trans-retinal

42
Q

Once the all-trans-retinal is transported to the RPE, what converts it to All-trans-retinyl

A

LRAT

43
Q

What converts All-trans-retinyl in the RPE to 11-cis-retinol?

A

RPE65

44
Q

Mutations in LRAT, RPE65 cause?

A

Retinitis Pigmentosa

45
Q

Retinitis Pigmentosa

A

Loss of night vision and peripheral vision due to accumulation of retinoid metabolites
- Causes photoreceptor degeneration and bony spicule formation

46
Q

Describe the Retinoid cycle

A

In Rod cell:
- 11-cis-retinal goes to all-trans-retinal and is released from opsin
- ABC transporter takes it to cytoplasm
- Converted to all-trans-retinol and taken to RPE
In RPE:
- LRAT takes all-trans-retinol to all-trans-retinyl ester
- RPE65 takes all-trans-retinyl to 11-cis-retinol
- Oxidized to 11-cis-retinal and taken back to rod cell

47
Q

Risk factors for macular degeneration?

A

Caucasion, obesity, smoker, old, diet

Neuroendocrine (47 decks)

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