Biochemistry Of Vision - 4/7 Seidler Flashcards
Rods have ____ sensitivity and ____ spatial resolution?
Cones?
High sensitivity, low spatial
Low sensitivity, high spatial
In the dark, Na channels on rods are what?
Describe the cell
What kind of nt release?
Na+ channels open
Depolarized
High rate of nt release
In the light what is the state of the Na+ channels on rods?
Describe the cell
Rate of nt release?
Closed
Hyperpolarized
Low rate of nt release
The disc membrane is what kind of system?
What is its photo receptor?
G-protein?
Effector protein?
GPCR
Rhodopsin
Transducin
Phosphodiesterase
At what wavelength is rhodopsin maximally absorbed?
What cofactor binds to its center?
500nm
Retinal
What is important for the absorption of retinal?
Proton attend schiff base interaction/linkage
Which Opsin proteins are located on the X chromosome?
What is their associated maximum absorption?
Red - 560
Green - 530
What is the absorption maxima for the blue Opsin? What chromosome is it located on?
Rod Opsin?
420nm - 7
500nm - 3
What is the molecular explanation for color blindness?
Non-homologous recombination
What causes “the perfect storm” for macular degeneration?
High O2 flux
High lipid content
UV rays
What are the macular carotenoids (xanthophylls)?
Lutein
Zeaxanthin
Beta-Caroten –> Retinol via what enzyme?
Where does this occur?
Dioxygenase
Intestinal mucosa
What is Retinol bound to in the body?
Retinol Binding Protein (RBP)
How does calcium ion affect guanylate cyclase?
Inhibits the activity of the enzyme
After illumination, how to the cone cells recover for activation?
Ca ion leaks out of the cell and this stimulates guanylate cyclase, thus restoring the [cGMP] to reopen the cGMP-gated channels
What enzyme deficiency has been shown to lead to retinitis pigmentsum?
LRAT and RPE65
In the Retinoid cycle, what happens 1st in the rod cell upon exposure to light?
What enzymatic process happens next?
11-CIS to all-trans
Reduction of all-trans-retinal to all-trans-Retinol
How does all-trans-Retinol leave the rod cell?
Where does it go?
iRBP
RPE and translocated to the ER
In the RPE what happens to all-trans-Retinol? Via what?
Then converted to what? By what?
Esterified to all-trans-retinyl ester by LRAT
11-cis-retinol by RPE65
Before it leaves the RPE, what does 11-cis-Retinol get converted to?
What exports it out of the RPE?
11-cis-retinal (oxidation)
iRBP
What happens to 11-cis-retinal after it has left the RPE?
Up taken into the rod cell and covalent attachment (schiff base) to Opsin forming a functional rhodopsin
Deficiencies in Vit A may manifest as what?
Night blindness
Visual impairment
Xerophthalmia (dry eyes)
Bitot’s spots (keratin in conjunctiva)
What upper respiratory problems may occur due to insufficient Vit A?
Bronchitis
Pneumonia
Excess Vit A causes what?
Liver toxicity
Joint pain
