[BIO] VITAMIN A

Question 1

Structure of vitamin A

Answer 1

Polyisoprenoid compound containing beta- ionone ring

Question 2

Forms of vitamin A

Answer 2

Precursor B-carotene
Retinol
Retinal
Retinoic acid

Question 3

Sources of vitamin A

Answer 3

Provitamin, carotenoids=carrots, apricots, sweet potato, cow milk

Preformed vit A, retinyl ester= Cod liver, yolk, liver &kidney

Question 4

Daily vitamin A requirement for males

Answer 4

900 RAE/day

Question 5

Daily vitamim A requirement for females

Answer 5

700 RAE/day

Question 6

Retinol carrier

Answer 6

RBP

Question 7

Retinoic acid carrier

Answer 7

Albumin

Question 8

B carotene carrier

Answer 8

VLDL

Question 9

Chylomicron is formed of

Answer 9

Retinyl ester+ B-carotene

Question 10

Micele is formed of

Answer 10

Retinol+ B-carotene

Question 11

Form stored in liver

Answer 11

Retinyl palmitate

Question 12

Functions of vitamin A (5)

Answer 12

1.Vision
2.Cell growth & differentiation
3.Reproduction
4.Antioxidant
5.Maintenance of healthy epithelium &mucous production

Question 13

Form associated w opsin

Answer 13

11-cis retinAl

Question 14

Rhodopsin is formed of

Answer 14

11-cis retinAl + opsin

Question 15

G-protein coupled serpentine receptor

Answer 15

Rhodopsin

Question 16

Form responsible for cell growth & differentiation of immune cells

Answer 16

Retinoic acid

Question 17

Form responsible for maintaining healthy epithelium & mucous production

Answer 17

Retinol

Question 18

Forms responsible for healthy reproduction

Answer 18

Retinol, Retinal

Question 19

Form responsible for antioxidant effect

Answer 19

Carotene

Question 20

Stimulates transcription for genes of cell growth & differentiation in immune cells

Answer 20

Retinoic acid

Question 21

Glycosyl carrier in glycoproteins & mucopolysaccharides synthesis

Answer 21

Retinol

Question 22

Retinyl-phosphate formed from

Answer 22

Retinol

Question 23

Support spermatogenesis & prevents fetal resorption in female rats

Answer 23

Retinol & Retinal

Question 24

Inactive in maintaining healthy epithelium & cell growth & differentiation

Answer 24

Retinoic acid

Question 25

Vitamin A deficiency is caused by

Answer 25

Decreased intake
Decreased absorption (biliary obstruction)
Decreased RBP (liver failure)

Question 26

Vitamin A deficiency symptoms

Answer 26

Nyctalopia
Xerophthalmia
Xeroderma
Keratomalacia
Keratinization of epithelium in GIT, GUT, RT
Impaired immunity

Question 27

Toxic hypervitaminosis A pathogenesis

Answer 27

Accumulation of unbound vitamin A causes membrane lysis+ tissue damage

Question 28

Toxic hypervitaminosis A symptoms

Answer 28

Dry skin
Alopecia
Hepatomegaly
Increased ICT
Teratogenicity

Question 29

Hypercarotenemia is differentiated from jaundice by

Answer 29

Scleral sparing

Question 30

Vitamim A clinical uses

Answer 30

Acne= 13-cis retinoic acid
Psoriasis= All Trans retinoic acid Pmyelocytic leukemia=All trans retinoic acid

Question 31

Reactions taking place during visual cycle

Answer 31

1. All Trans retinAl
   ~~~isomerization+Reduction~~~
2. All Trans retinOl
   ~~~esterification~~~
3. All Trans retinyl ester
   ~~~isomerizarion~~~
4. 11-Cis retinOl
   ~~~oxidation~~~
5. 11-cis retinAl
6. 11-cis retinAl+ opsin= rhodopsin

Question 32

In intestinal lumen

Answer 32

1.Retinyl ester—>retinOl (hydrolysis)
2.Free retinol+ B-carotene+Bile= Micele

Question 33

In enterocytes

Answer 33

1.Retinol—> Retinyl ester (Re-esterification)
2. B-carotene–> 2 free retinAl (cleavage by carotenase)
3. 2 free retinAls–> retinOl
(Reduction)
4. Retinol–>retinyl ester(esterification)
4. Retinyl ester+ B-carotene= Chylomicron
5. Chylomicron exocytosis to lymphatics then blood

Question 34

In liver

Answer 34

1.Retinyl ester–> retinol (hydrolysis)
2.Retinol–> RBP
Or
Retinol–>retinoic acid (oxidation)
3. B-carotene–> VLDL–> adipose tissue