MNSR 33 -Chemistry of the Eye

Question 1

when does geometric isomerism occur?

Answer 1

Some substituted alkenes Some substituted cycloalkanes

Some square planar and octahedral complexes having different ligands

Question 2

why does geometric isomerism arise in alkenes?

Answer 2

C-C double bond made of sigma and pi pond
pi bond is weaker than sigma bond.
Double bond causes the molecule to lose the ability to freely rotate.
Can create multiple structures

Question 3

when is geometric isomerism only possible in alkenes

Answer 3

carbons must have 2 different groups

Question 4

interconverted definition and how can this occur

Answer 4

molecule can go from trans to cis or cis to trans

can be done thru energy e.g. light and heat by rotating C-C sigma bond and reforming pi bond

Question 5

How to determine if it is E or Z molecule

Answer 5

look at substituent at C-C- double bond
atoms of higher atomic no. attached to doubly bounded C are taken to priority
double bonds take higher priority than single
higher = higher priority
lower = lower priority substituents
higher on same side = Z-
higher subs on different side = E

Question 6

how many rods in the eye

Answer 6

120 million rods

Question 7

how many cones in the eye

Answer 7

7 million cones

Question 8

chromophore

Answer 8

light absorbing group e.g. 11-cis-retinal

Question 9

describe chemistry of 11-cis-retinal

Answer 9

penta-ene and an aldehyde

Question 10

what does 11-cis-retinal combine w/ and what is its product

Answer 10

combines w/ protein opsin to make rhodopsin

Question 11

what event takes place in rhodopsin

Answer 11

The primary event involves isomerisation at the C(11)-C(12) double bond.

Question 12

what do rod cells contain

Answer 12

rhodopsin

Question 13

rhodopsin reaction mechanism

Answer 13

reacts with a photon of light isomerizes into all trans retinal (bathorhodopsin)
does not fit well with protein and is energetically unfavourable and undergoes a series of change

Question 14

list of pigment names 11-cis-retinal makes

Answer 14

Rhodopsin
Bathorhodopsin
Lumirhodopsin
Metarhodopsin I
Metarhodopsin II
trans-Retinal (free)

Question 15

enzyme present in vision cycle

Answer 15

retinal isomerase

Question 16

vision cycle

Answer 16

go back to it slide 24

Question 17

Importance of vitamin A

Answer 17

precursor to retinal 11-trans-retinol
has CH2OH instead of CHO
Is converted to rhodopsin

Question 18

Vitamin A to rhodopsin cycle

Answer 18

Vitamin A –Retinol dehydrogenase –> 11-trans-retinal —Retinal
isomerase–>. 11-cis-retinal —opsin–> Rhodopsin

Question 19

Why are carrots important for eye vision

Answer 19

contain beta carotene

the enzyme beta carotene dioxygenase converts the beta carotene into vitamin A

Question 20

where is vitamin A formed

Answer 20

in walls of small intestine

Question 21

where is retinol stored

Answer 21

stored in liver

Question 22

A deficiency in vitamin a leads to..

Answer 22

a deficiency of rhodopsin and causes night blindness (inability to see in low intensity light).

Question 23

where is vitamin A in food

Answer 23

cod liver oil, halibut oil, egg yolk, apricots, peaches.