MNSR 33 -Chemistry of the Eye Flashcards
when does geometric isomerism occur?
Some substituted alkenes Some substituted cycloalkanes
Some square planar and octahedral complexes having different ligands
why does geometric isomerism arise in alkenes?
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
when is geometric isomerism only possible in alkenes
carbons must have 2 different groups
interconverted definition and how can this occur
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
How to determine if it is E or Z molecule
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
how many rods in the eye
120 million rods
how many cones in the eye
7 million cones
chromophore
light absorbing group e.g. 11-cis-retinal
describe chemistry of 11-cis-retinal
penta-ene and an aldehyde
what does 11-cis-retinal combine w/ and what is its product
combines w/ protein opsin to make rhodopsin
what event takes place in rhodopsin
The primary event involves isomerisation at the C(11)-C(12) double bond.
what do rod cells contain
rhodopsin
rhodopsin reaction mechanism
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
list of pigment names 11-cis-retinal makes
Rhodopsin Bathorhodopsin Lumirhodopsin Metarhodopsin I Metarhodopsin II trans-Retinal (free)
enzyme present in vision cycle
retinal isomerase
vision cycle
go back to it slide 24
Importance of vitamin A
precursor to retinal 11-trans-retinol
has CH2OH instead of CHO
Is converted to rhodopsin
Vitamin A to rhodopsin cycle
Vitamin A –Retinol dehydrogenase –> 11-trans-retinal —Retinal
isomerase–>. 11-cis-retinal —opsin–> Rhodopsin
Why are carrots important for eye vision
contain beta carotene
the enzyme beta carotene dioxygenase converts the beta carotene into vitamin A
where is vitamin A formed
in walls of small intestine
where is retinol stored
stored in liver
A deficiency in vitamin a leads to..
a deficiency of rhodopsin and causes night blindness (inability to see in low intensity light).
where is vitamin A in food
cod liver oil, halibut oil, egg yolk, apricots, peaches.
