Biochemistry
Nutrition
Compiled By Simon Mwangi
Edition: 2024/25
, Science | Biochemistry I of XXIII pages
1. Give a general description of Vitamin A
collectively called retinoids
Retinol: transport and storage form of vitamin A
11-cis retinal is required for vision
Retinol and retinal can be easily interconverted.
Retinoic acid: epithelial growth and differentiation. It has steroid hormone like effect.
2. Describes the steps of the absorption and transport of Vitamin A
Diet contain Retinol esters -> hydrolysis by intestinal mucosa releasing Retinol and free fatty acids ->
and secretion in chylomicrons which are taken up by the liver where it is stored -> plasma Retinol binding
in the liver transports to extra hepatic tissues -> tissues contain cellular Retinol binding protein that carries
3. List the sources of Vitamin A
Liver, kidney, butter and cream products; egg yolks
- Yellow vegetables and fruits ( dietary pro vitamin form: B-carotene)
4. What are the functions of Vitamin A?
Vision: 11 cis retinal is a component of rhodopsin (visual pigment). Visual cycle req isomerization b/w cis and
Maintenance of specialized epithelia, esp mucus secreting cells (Retinoic acid)
Growth (Retinoic acid)
Reproduction (Retinol)
5. Describe the mechanism of action of Retinoic acid in epithelia cells.
1) Retinol enters target cell and is oxidized to Retinoic Acid in cytosol2) Retinoic Acid moves from cytosol
nucleus with help of Retinoid Binding Proteins3) Retinoic Acid binds to nuclear receptors forming an
receptor complex 4) Retinoic acid-receptor complex binds to chromatin activating the transcription of specific
6. Describes the steps in the visual cycle pathway
Retinol (transported in blood in the form of all-trans Retinol) enters retinal pigment epithelium.
Esterfied to All-trans retinyl ester
becomes 11-cis Retinol
oxidized to 11-cis Retinal
11-cis retinal enters rod cell where it combines with opsin to form rhodopsin (visual pigment).
absorption of light photon catalyzes isomerization of 11-cis retinal to all-trans Retinal triggering eventual
Opsin becomes available again and All-trans retinal eventually becomes all-trans Retinol.
all trans Retinol goes back to retinal pigment epithelium to renter cycle.
7. What causes Vitamin A deficiency?
Dietary deficiency most common - fat free diet
Fat malabsorption
8. What are some signs and symptoms of Vitamin A deficiency?
Night blindness
Xerophthalmia
Bitots spots
Keratomalacia
increased risk of pulmonary infections
immune deficiency - weakened innate immunity
Biochemistry 2024/25 Edition
, Science | Biochemistry II of XXIII pages
9. What is Night blindness and what is the cause?
Earliest of the symptoms of Vitamin A deficiency.
inability to see Dim light
reversible
10. What is Xerophthalmia and what is the cause?
Vitamin A deficiency that produces dryness of the conjunctiva and cornea.Reversible
11. What treatment is Retinoic acid given for?
Acne treatment, especially topical form
12. What is all-trans Retinoic acid used in treatment of?
Acute promyelocytic leukemia
13. What can hypervitaminosis of Vitamin A cause?
Raised intracranial pressure leading to headaches - may mimic brain rumors
Dry and pruritic skin
enlarged liver
can cause spontaneous abortions and congenital malformations in the fetus during pregnancy.
14. What is the name for vitamin D found in plants?
Ergocalciferol (D2)
15. What is the general name for vitamin D found in animals?
Cholecalciferol (D3)
16. What is the name of the precursor for Cholecalciferol synthesis in skin?
7-Dehydroxycholesterol(intermediate in cholesterol synthesis)
(Cholecalciferol is Vitamin D3)
17. What are other names for the active form of Vitamin D?
Calcitriol
* 1,25 dihydroxy cholecalciferol
18. In Vitamin D synthesis, what is the first step?
7-dehydrocholesterol in the skin is activated by sunlight to form Cholecalciferol.
Or
Cholecalciferol is taken in through diet.
19. Regarding the steps of Vitamin D synthesis, what happens to Cholecalciferol?
Goes to liver (from skin or diet) and, through enzyme 25-Hydroxylase, becomes 25-hydroxycholecalciferol.
20. Regarding the steps of Vitamin D synthesis, what happens in the kidney?
25-hydroxycholecalciferol (from liver) is converted into 1,25-dihydroxycholecalciferol/Calcitriol (active form
21. Which is the regulated step in Vitamin D synthesis and how is it regulated?
Biochemistry 2024/25 Edition
Nutrition
Compiled By Simon Mwangi
Edition: 2024/25
, Science | Biochemistry I of XXIII pages
1. Give a general description of Vitamin A
collectively called retinoids
Retinol: transport and storage form of vitamin A
11-cis retinal is required for vision
Retinol and retinal can be easily interconverted.
Retinoic acid: epithelial growth and differentiation. It has steroid hormone like effect.
2. Describes the steps of the absorption and transport of Vitamin A
Diet contain Retinol esters -> hydrolysis by intestinal mucosa releasing Retinol and free fatty acids ->
and secretion in chylomicrons which are taken up by the liver where it is stored -> plasma Retinol binding
in the liver transports to extra hepatic tissues -> tissues contain cellular Retinol binding protein that carries
3. List the sources of Vitamin A
Liver, kidney, butter and cream products; egg yolks
- Yellow vegetables and fruits ( dietary pro vitamin form: B-carotene)
4. What are the functions of Vitamin A?
Vision: 11 cis retinal is a component of rhodopsin (visual pigment). Visual cycle req isomerization b/w cis and
Maintenance of specialized epithelia, esp mucus secreting cells (Retinoic acid)
Growth (Retinoic acid)
Reproduction (Retinol)
5. Describe the mechanism of action of Retinoic acid in epithelia cells.
1) Retinol enters target cell and is oxidized to Retinoic Acid in cytosol2) Retinoic Acid moves from cytosol
nucleus with help of Retinoid Binding Proteins3) Retinoic Acid binds to nuclear receptors forming an
receptor complex 4) Retinoic acid-receptor complex binds to chromatin activating the transcription of specific
6. Describes the steps in the visual cycle pathway
Retinol (transported in blood in the form of all-trans Retinol) enters retinal pigment epithelium.
Esterfied to All-trans retinyl ester
becomes 11-cis Retinol
oxidized to 11-cis Retinal
11-cis retinal enters rod cell where it combines with opsin to form rhodopsin (visual pigment).
absorption of light photon catalyzes isomerization of 11-cis retinal to all-trans Retinal triggering eventual
Opsin becomes available again and All-trans retinal eventually becomes all-trans Retinol.
all trans Retinol goes back to retinal pigment epithelium to renter cycle.
7. What causes Vitamin A deficiency?
Dietary deficiency most common - fat free diet
Fat malabsorption
8. What are some signs and symptoms of Vitamin A deficiency?
Night blindness
Xerophthalmia
Bitots spots
Keratomalacia
increased risk of pulmonary infections
immune deficiency - weakened innate immunity
Biochemistry 2024/25 Edition
, Science | Biochemistry II of XXIII pages
9. What is Night blindness and what is the cause?
Earliest of the symptoms of Vitamin A deficiency.
inability to see Dim light
reversible
10. What is Xerophthalmia and what is the cause?
Vitamin A deficiency that produces dryness of the conjunctiva and cornea.Reversible
11. What treatment is Retinoic acid given for?
Acne treatment, especially topical form
12. What is all-trans Retinoic acid used in treatment of?
Acute promyelocytic leukemia
13. What can hypervitaminosis of Vitamin A cause?
Raised intracranial pressure leading to headaches - may mimic brain rumors
Dry and pruritic skin
enlarged liver
can cause spontaneous abortions and congenital malformations in the fetus during pregnancy.
14. What is the name for vitamin D found in plants?
Ergocalciferol (D2)
15. What is the general name for vitamin D found in animals?
Cholecalciferol (D3)
16. What is the name of the precursor for Cholecalciferol synthesis in skin?
7-Dehydroxycholesterol(intermediate in cholesterol synthesis)
(Cholecalciferol is Vitamin D3)
17. What are other names for the active form of Vitamin D?
Calcitriol
* 1,25 dihydroxy cholecalciferol
18. In Vitamin D synthesis, what is the first step?
7-dehydrocholesterol in the skin is activated by sunlight to form Cholecalciferol.
Or
Cholecalciferol is taken in through diet.
19. Regarding the steps of Vitamin D synthesis, what happens to Cholecalciferol?
Goes to liver (from skin or diet) and, through enzyme 25-Hydroxylase, becomes 25-hydroxycholecalciferol.
20. Regarding the steps of Vitamin D synthesis, what happens in the kidney?
25-hydroxycholecalciferol (from liver) is converted into 1,25-dihydroxycholecalciferol/Calcitriol (active form
21. Which is the regulated step in Vitamin D synthesis and how is it regulated?
Biochemistry 2024/25 Edition
