Vitamin A Flashcards
Who was Paul Karrer?
Awarded for his investigations on carotenoids.
What are the different forms of retinoids?
All-trans-retinol
Retinal
Retinoic Acid
Retinyl ester
What are the interconversions of the retinoids?
Retinol Retinal (can be reversibly oxidized) Retinal ----> Retinoic Acid (can be irreversibly oxidized)
Retinal —> Retinoic acid is active in what?
Active in growth but not vision or reproduction
What is the enzyme that oxidizes Retinal to Retinoic Acid?
Retinal Oxidase
What are the different forms of carotenoids?
Beta-carotene- most common in foods
Alpha-carotene
Gamma-carotene
What is Vitamin A
It is the generic descriptor for compounds exhibiting the biological activity of retinoids and some provitamin A carotenoids
Retionol (as all-trans) is usually bound to?
Fatty acid esters (palmitate)
Retinyl Palmitate and carotenoids are usually bound to what?
Protein
What are the food forms of Vitamin A?
Retinyl Palmitate and Beta-Carotene
What is CRBPII?
Cellular retinol-binding protein II
Abundant in small intestine
Binds retinol and retinal (makes them soluble)
-this controls free retinol concentrations and protects it from oxidation.
-directs the reduction of retinal to retinol
-Escorts retinol to LRAT
What is LRAT?
Lecithin retinol acyl transferase
Adds fatty acids (mainly palmitate) to retinol to form retinyl esters
What does the formation of the trimolecular complex do?
It reduces glomerular filtration and thus renal catabolism
Vitamin A functions metabolically in…?
Vision, cellular differentiation & gene expression, growth, immune system, bone development, reproduction.
What is Vitamin A’s role in vision?
Serves as the photosensitive chromophoric group of rhodopsin found in rod cells of the retina.
What does rhodopsin detect?
Small amounts of light important for night vision
What is the purpose of the visual cycle?
To regenerate 11-cis-retinal
What must happened in order to regenerate rhodopsin?
All-trans-retinal must be converted back to 11-cis-retinal
How can stored retinyl esters be used to produce 11-cis-retinal?
They can hydrolyzed, isomerized, oxidized to 1–cis-retinal and shuttled to rod cell.
If storage is deficient, cannot regenerate sufficient 11-cis retinal
Failure to regenerate 11-cis-retinal results in?
Night blindness
What is cellular differentiation?
Process whereby an immature cell is transformed into a specific type of mature cell
What is the reaction in cell differentiation that Vitamin A is involved in?
Keratinocytes ——–> (Retinoic acid)——> epidermal cells (immature skin cells)
Squamous epithelial keratinizing cells —–> (retinoic acid) —–> Mucous-secreting cells
*If retanoic acid is not there, the squamous epithelial keratinizing cells replace the mucous secreting cells and cause keratinization, which is the dry, rough, and scaly skin.
Cell differentiation is important for what?
Bronchial passages which a barrier function which include mucous-secreting cells nd ciliated cells.
A deficiency in Vitamin A may compromise what in regards to immunity and increase what?
Comprimise barrier function and increase risk of infection.
What does CRABP stand for and what does it serve for?
Cellular retinoic acid binding protein and it serves as a chaperone that binds to All-trans-retinoic acid and 9-cis retinoic acid and translocates them into the nucleus