BoV - Seidler Flashcards
What are the sensitivity and resolution properties of cones vs rods?
Cones: low sensitivity, high resolution
Rods: high sensitivity, low resolution
What layer are photoR’s “plugged” in to? What is the state of the discs closest to this layer?
Pigment epithelial layer at the very back of the retina.
These discs are old and ready to be replaced because they’ve been damaged by light and O2
What are the two molecules that make rhodopsin? What kind of R is it? What bond is present and important here? What’s the important co-factor of rhodopsin?
Opsin and 11-cis-retinal
7TM R that closely resembled b2-adrenergic R’s
The Schiff base covalent bond where 11-cis-retinal is attached to a lysine in the opsin
Vit-A
How many genes are associated with photoR’s? What are the proteins they create?
4
rhodopsin, red opsin, green opsin, blue opsin
Which opsin genes are located on the X chromosome? What are the locations of the other photoR genes?
Red opsin, green opsin
Blue opsin on chromosome 7, rhodopsin on chromosome 3
What causes macular degeneration? What protects against this dx?
High O2 exposure, high lipid content, UV rays
Xanthophylls/Carotenoids
What are the two carotenoids/xanthophylls mentioned?
Lutein
Zeaxanthin
What are sx of Vit A deficiency?
Night blindness, dry and scaly skin, xerophthalmia (dry eyes), keritinization of GI and respiratory epithelium
What enzyme turns beta-Carotene –> (2) Retinol? Where does this reaction occur? What protein transports Retinol in blood plasma?
Dioxygenase
In the intestinal mucosa
Retinol binding protein
What enzyme initiates transduction termination of Rhodopsin? What does this do?
Rhodopsin Kinase
Phosphorylates the C-terminus of Rhodopsin (serine and threonine residues), creating a binding spot for B-arrestin that ceases Rhodopsin interaction with Transducin
What is the function of guanylate cyclase? What blocks it? When does and doesn’t the block occur?
To make cGMP which activates the Na channels
Ca blocks it
The block occurs when no light is present and many channels are open and enough Ca leaks in. No block occurs when Ca levels are very low, when light is present because the leak channels are shut down and an exchanger is constantly pumping Ca out.
What ion thermodynamically favorable exchange is made to extrude a Ca ion from rod cytoplasm?
4 Na are taken in – 1 K is kicked out, and thus there’s enough energy generated to extrude 1 Ca ion
What types of channels are ultimately inactivated by light in rods?
Na channels
