B10

Question 1

Explain the role of cis- and trans- retinal in vision.

Answer 1

• vitamin A is oxidized to cis- retinal
• it has a conjugated system which allows for absorption of visible light
• cis-retinal is bound to opsin and forms rhodopsin
• visible light absorbed by Cis-retinal which is converted into trans-retinal
• 11-trans retinal no longer fit
  into the rhodopsin.
• It leads to the conformational change in rhodopsin triggering an impulse to be sent to the brain
• trans retinal is converted back to cis-retinal through enzyme activity

Question 2

Most naturally occuring carbohydrates are…

Answer 2

D
(chiral carbon atom furthest away from the ketone or aldehyde group has OH hroup on the dexter (right side))

Question 3

what is the difference between alpha and beta monosaccharides?

Answer 3

alpha have OH group below the plane of the ring

Question 4

glycogen, starch, cellulose compare the structure

Answer 4

• cellulose beta, 1-4- glycosidic bonds
• starch (amylose and amylopectin (1,4 and 1,6) alpha linkages)
• glycogen alpha 1,4 and 1,6 but more branched than starch

Question 5

What fatty acids have higher boiling point and why?

Answer 5

• trans becasue they are straight and can be packed more closely, stronger London forces

Question 6

In what form do fatty acids exist?

Answer 6

19/20 (glycine doesn’t have a chiral carbon) exist in L form
CORN spelled to the left (anticlockwise) 🔄
They are levorotatory meaning they rotate the plane of plane polarized light to the left

Question 7

In what process are unsaturated fatty acids converted to their trans form (partial…) or saturated fatty acids?

Answer 7

Hydrogenation, Ni as a catalyst
In partial hydrogenation - cis to trans
In hydrogenation - unsaturated to saturated
Hydrogenation makes fats harder ( because increase in melting point)
Decreases the rate of oxidation (longer shelf life)
Trans fats are Hard to metabolize, they accumulate in the body

Question 8

Why are trans fats unhealthy?

Answer 8

They increase LDL levels
Lower HDL levels