Fat soluble vitamins Flashcards Preview

Vitamins and Enzymes > Fat soluble vitamins > Flashcards

Flashcards in Fat soluble vitamins Deck (31):

Fat soluble vitamins

A, D, E K


Vitamin A (4)

retinol, retinal, retinoic acid and B- carotene


Vitamin A
- function (3)

-visual pigments in retina,
-regulation of gene expression and cell differentiation
-B- carotene is an antioxidant


Vitamin A
-distribution (6)

-Egg yolk
-yellow and dark green vegetables


Vitamin A
-absorption (3)

1. Retinyl esters present in the diet are hydrolyzed in the intestinal mucosa, releasing retinol and free fatty acids.

2. Retinol derived from esters and from the cleavage and reduction of carotenes is reesterified chylomicrons (long-chain fatty acids in the intestinal mucosa)

3. Retinyl esters contained in chylomicron remnants are taken up by, and stored in, the


Vitamin A
-transport (2)

1. Retinol is released from the liver and transported to extrahepatic tissues by the plasma retinol- binding protein (RBP).

2. RBP complex attaches to specific receptors on the surface of the cells of peripheral tissues, permitting retinol to enter.


Regulation of Gene Expression (3)

1. Retinol is oxidized to retinoic acid.
2. Retinoic acid binds with high affinity to specific receptor proteins present in the nucleus.
3. The activated retinoic acid– receptor complex regulates retinoid-specific RNA synthesis.


Vitamin A
-In the retina, retinal functions as
-opsin proteins

-the prosthetic group of the light-sensitive opsin proteins
-rhodopsin (in rods) and iodopsin (in cones)/


Vitamin A
-When rhodopsin is exposed to light,

a series of photochemical isomerization occurs, results in release of all-trans retinal and opsin, triggers a nerve impulse that is transmitted by the optic nerve to the brain.


Vitamin A

-Night blindness
-Keratinization of skin


Vitamin A
-toxicity (3)

-Hypervitaminosis A: excessive intake of vitamin A
-Unbound vitamin A causes tissue damage
-Skin lesions, enlarged liver, calcification of soft tissues


Vitamin D (4)

-have a hormone- like function
-Cholecalciferol (vitamin D3)
-Ergocalciferol (vitamin D2)
-can be synthesized in the skin


Vitamin D (3)
-synthesis in the skin

1. 7- dehydrocholesterol accumulates in the skin.
2. undergoes a non-enzymatic reaction on exposure to ultraviolet light
3. pre- vitamin D3


Vitamin D
-dietary sources

Ergocalciferol --> found in plants

Cholecalciferol --> found in animal tissues


Vitamin D
-metabolism (3)

1. In the liver cholecalciferol is hydroxylated to form the 25-hydroxyderivative, calcidiol.

2. It is released into the circulation bound to a vitamin D binding globulin

3. In the kidney, calcidiol undergoes 1-hydroxylation

4. yield the active metabolite 1,25-dihydroxy-vitamin D (calcitriol).


Vitamin D
-regulation in metabolism (2)

-Vitamin D’s formation is regulated by the level of plasma phosphate and calcium.
-activity is increased directly by low plasma phosphate or indirectly by low plasma calcium, which triggers the release of parathyroid hormone (PTH).


Vitamin D

To maintain adequate plasma levels of calcium.


Vitamin D performs its function by: (3)

-increasing the uptake of calcium by the intestine
-minimizing loss of calcium by kidney
-stimulating resorption of bone when necessary


Vitamin D

-Rickets in children
-Osteomalacia in adults


Vitamin K
-3 compounds that have biological activity of it

-Phylloquinone: normal dietary source
-Menaquinones: synthesized by intestinal bacteria
-Menadione: can be metabolized to phylloquinone, synthetic.


Vitamin K

-posttranslational modification of various blood clotting factors (prothrombin and blood clotting factors II, VII, IX, and X).
- synthesis of bone calcium-binding proteins


Vitamin K
-Two proteins that contain γ-carboxyglutamate are present in bone:

osteocalcin and bone
matrix Gla protein.


Vitamin K

found in cabbage, kale, spinach, egg yolk, and liver.


Vitamin K

synthesized by the bacteria in the gut.


Vitamin K

It is unusual



-Are used to reduce blood coagulation in patients at risk of thrombosis;
-The most widely used is warfarin.


Vitamin E
-consists of
-the most active is

-eight naturally occurring tocopherols.
-α –tocopherol is the most active


Vitamin E

It is as an antioxidant in prevention of the non-enzymic oxidation of cell components by molecular oxygen and free radicals.


Vitamin E

Vegetable oils are rich sources of vitamin E, whereas liver and eggs contain small amounts


Vitamin E
-deficiency (3)

-In humans is unknown.
-Might be in patients with severe fat mal-absorption, cystic fibrosis.
-some forms of chronic liver disease


Vision process in the retina

1. 11- cis retinal is bound to opsin.
2. absorption of a photon of light by the 11- cis retinal causes the structure to flip back to trans configuration
3. it is the change in structure that provides the first signal in our eyes that light has been detected.