Ocular Proteins

Question 1

Crystallin’s general info

Answer 1

group of water-soluble protein found in the epithelial and fiber cells of the ocular lens
3 types: alpha, beta & gamma crystallins

Question 2

crystallins role in the eye

Answer 2

maintain shape of the lens, affect how light is refracted in the lens, and act as molecular chaperones

Question 3

alpha-crystallins

Answer 3

function as a molecular chaperone:
- maintain normal conformation/folding of other crystallins
-inhibit crystallin aggregation, which leads to cataracts

Question 4

crystallin age-related transformations (5 of them)

Answer 4

phosphorylation, disulfide bond formation, deamidation, peptide bond disruption, & glycation

Question 5

crystallin transformation results

Answer 5

change the ratio of water soluble to insoluble lens proteins
- cataracts means larger increase in insoluble proteins, decreasing the ratio of soluble: insoluble proteins

Question 6

how cataracts form?

Answer 6

in normal lens, reactive AA’s are “buried”
when biochemical transformations occur, oxidizable groups are exposed
leads to aggregate formation

Question 7

nuclear sclerotic cataracts

Answer 7

changes in tryptophan within crystallins

Question 8

cortical cataracts

Answer 8

increase in membrane permeability of lens fiber cells with age, leads to over hydration, lens swelling and rupture
which forms debris fragments and crystallin aggregates

Question 9

Rhodopsin protein function

Answer 9

initiates the transduction process of light energy being converted into electrical signaling, in the retina

Question 10

Rhodopsin protein structure

Answer 10

transmembrane protein, G-protein coupled receptor, % Vit A prosthetic group

Question 11

what is rhodopsin without Vit A?

Answer 11

Opsin

Question 12

mucous glycoproteins (mucins)

Answer 12

found in precorneal tear film, associated w/ 2 sublayers within the mucin layer
-glycocalyx layer: membrane-bound mucins
- mucous: free mucins

Question 13

mucin function

Answer 13

primarily secreted by conjunctival goblet cells
- are a protective barrier for the cornea

Question 14

conditions that cause irregular mucin

Answer 14

Vit A deficiency, stevens-Johnson syndrome, alkali burns

Question 15

corneal stroma collagen

Answer 15

contains Type I, V, VI (mainly I)
- type V limits type I diamater, which prevents light scattering
- type VI stabilizes proteogylcans and keratocytes

Question 16

vitreous humor collagen

Answer 16

contain type II (vitrosin) & IX, which are arranged in parallel orientation across all of the vitreous humor

Question 17

type IV basement membrane collagen

Answer 17

tissue sheet that supports or separates cells from other noncellular parts of a tissue
- type IV, in bowman’s membrane, descemet’s membrane, lens capsule, and blood vessels

Question 18

type VII basement membrane collagen

Answer 18

are anchoring fibrils
Ex. extend from corneal epithelium through bowman’s and adheres to the stroma layer

Question 19

keratoconus

Answer 19

corneal thinning/steepening due to loss of connective proteins & collagen within the cornea