Quiz 2 (Phototransduction, Color Vision, Color Blindness, Nutrition)

The C-terminus of rhodopsin is located where?

The cytoplasm

The N-terminus of rhodopsin is located where?

The lumen of the disk

In addition to transducin, the RGS9 complex is comprised of what?

R9AP, PDE6γ, Gβ5, RGS9

Following phototransduction activation, activated rhodopsin is shut off by what?

C-terminal phosphorylation by rhodopsin kinase and arrestin binding

cGMP is replenished after phototransduction by what?

a decrease of calcium that leads to activation of guanylate cyclase

What is the "M" pigment?

Green

What is the "L" pigment?

Red

What is the "S" pigment?

Blue

????

a shift in the maximum absorbance to a shorter wavelength

To provide sufficient information to the brain to restore face recognition levels of vision through a prosthetic device, it's estimated that a least a _____ microelectrode array will be required.

200

Rhodopsin activates what?

Transducin

Transducin activates what?

PDE6

What does PDE6 do?

Catalyzes hydrolysis of cGMP

What does a decreased amount of cGMP do?

closes gated cation channels

Why does the photoreceptor hyperpolarize?

Na+ ions can no longer enter the cell

What does the change in the membrane potential cause?

VG calcium channels to close

What does a decrease of Ca2+ lead to?

A near 0 concentration of glutamate

What is the average length of an outer segment of a photoreceptor?

100 μm

What is the average width of an outer segment of a photoreceptor?

2 μm

T/F: Cones are the most abundant photoreceptor in humans

False, rods are more abundant

T/F: Rods are much faster than are cones

False, rods have relatively slow time resolution

T/F: Cones are much less sensitive than rods

True

Are rods or cones responsible for color vision?

Cones

What happens in the inner segment of a photoreceptor?

Normal cellular functions

Is there greater current in the dark or in the light for photoreceptor cells?

Dark

T/F: Glutamate output is higher in the dark

True

What actually leads to the hyperpolarization of a photorecpetor?

A decrease of cGMP concentration

What are some blinding diseases that are caused by rhodopsin mutations?

Autosomal dominant retinitis pigmentosa, congenital stationary night blindness

Are cyclic nucleotide gated channels open or closed in the dark?

Open

What activated receptor catalyzes GDP-GTP exhange on the G-protein?

MII

What is the full name of PDE6?

PDE6⍺βγγ

What is the rate-limiting step in the recovery of the visual response?

the hydrolysis of GTP to GDP

What is the key to adaptation of the visual response?

Ca2+

Which cone is present in the highest number?

Red cones

Which cone is present in lowest number?

Blue cones

Where does isomerization of retinal take place in cones?

Müller cells

Where does the isomerization of retinal take place in rods?

the RPE

Vitamin A2 is shifted toward the red end of the spectrum by how many nm?

25 nm

Is color blindness an X- or Y-linked mutation?

X-linked

What chromosome is the blue/yellow gene found?

7

What is monochromacy?

When two (or all three) of the cone pigments are missing

What is dichromacy?

When only one of the cone pigments is missing

Is monochromacy total color blindness?

Yes

T/F: Red/green color blindness is an example of dichromacy

True

What is the ratio of men who experience color blindness?

1:12

What is the ratio of women who experience color blindness?

1:200

Why do women experience color blindness at such a low rate, relative to men?

If a woman has the gene on one X chromosome, chances are that that X chromosome will be masked by the other X chromosome

What is deuteranomaly?

Green looks more red

What is protanomaly?

Red looks more green and less bright

What is the most common form of colorblindness?

Deuteranomaly

What are protanopia and deuteranopia?

The inability to distinguish between red and green at all

What is tritanomaly?

Difficulty in differentiating between blue and green and yellow and red

What is tritanopia?

The inability to tell the difference in blue and green, purple and red, and yellow and pink. It also makes colors appear muted

What is achromatopsia?

An example of monochromacy; seeing the world in shades of gray

What test is performed to screen for colorblindness?

Ishihara test

What is the chance of having achromatopsia?

1:30,000

What is nystagmus?

Rapid involuntary eye movement

What is photophobia?

Painful sensitivity to light

What is visual acuity?

sharpness of vision

Which gene is the cause of achromatopsia, most often?

CNGB3

Is there a cure for inherited colorblindness?

No

Who was the first person to describe colorblindness?

John Dalton

What nutrient is thought to be an antioxidant that could protect photoreceptor cells in the macular region?

Lutein

What nutrients were studied in the AREDS clinical trial?

zinc, β-carotene, and vitamins C and E

How does a retinal prosthesis work?

Electrical stimulation bypasses the defective/dead photoreceptors and stimulates the remaining non-photoreceptor cells of the retina