Vitamin A and Carotenoids Flashcards
retinoids comprise both __ and __ species that bear a structural resemblance to __, with or without the biological activity of __
retinoids comprise both natural and synthetic species that bear a structural resemblance to all-trans-retinol, with or without the biological activity of vitamin A
main function of Vitamin A
growth factor at all stages in life
6 biological functions of vitamin A
- bone formation
- vision
- immune
- cell growth and differentiation
- reproduction
- organ development
In cell growth and differentiation, vitamin A becomes a __ that affects a large number of genes
In cell growth and differentiation, vitamin A becomes a transcription that affects a large number of genes
vitamin A is a subgroup of __
vitamin A is a subgroup of retinoids
biologically active form of vitamin A
all-trans retinol
storage form of Vitamin A
retinyl-esters
transport form of Vit A
all-trans retinol
all-trans retinol
- transport form of Vit A
- substrate for making biologically active Vit A
- active form of Vit A, bc it is the precursor
oxidation of all-trans-retinol produces __ which is transported into __ and used in several __
oxidation of all-trans-retinol produces all-trans-retinal which is transported into cells and used in several biological pathways
all-trans retinoic acid requireds __ to be a __ factor derived from __
all-trans retinoic acid requires 9-cis-retinoic acid to be a transcription factor derived from Vit A
retinyl ester = retinol + __
retinyl ester = retinol + fatty acid (FA)
retinyl esters are the __ form of vitamin A stored primarily in the __
retinyl esters are the storage form of vitamin A stored primarily in the liver
retinyl-esters are the __ form of Vitamin A in __
retinyl-esters are the transportable form of Vitamin A in chylomicrons
11-cis-retinal is a __ factor that controls __ and is necessary for formation of __
11-cis-retinal is a transcription factor that controls nocturnal vision and is necessary for formation of rhodopsin
13-cis-retinoic acid aka __ is a __ __ factor and is a more __ form of retinoic acid
13-cis-retinoic acid aka accutane is a synthetic transcription factor and is a more potent/active form of retinoic acid
carotenoid structure
2 retinal attached
3 most abundant carotenoids
- beta-carotene
- alpha-carotene
- lycopene
__ and __ can be converted into trans-retinal
beta-carotene and alpha-carotene can be converted into trans-retinal
lycopene is a __, but can’t be converted to __
lycopene is a essential antioxidant, but can’t be converted to vit A
where do animals get carotenoids?
diet, we can’t make them de novo
2 chemical forms of carotenoids
- carotenes
- xantophylls
carotenes are made of __ and __ and include __, __, and __
carotenes are made of hydrogen and carbon and include beta and, alpha-carotene, and lycopene
xantophylls have at least one __ and include __ and __
xantophylls have at least one oxygen and include beta and alpha-crypyoxanthin
pro-vitamin definition
substance that can be converted to a vitamin
Provitamin A
- beta-carotene
- alpha-carotene
- beta-cryptoxanthin
- alpha-cryptoxanthin
non-provitamin A
- lycopene
- zeaxanthing
- lutein
main food form of vitamin A
retinyl esters
2 enzymes that promote synthesis of retinyl esters
LRAT and ARAT
retinoid metabolism steps overview
- retinyl esters obtained from diet
- retinyl esters to retinol
- retinol transported into cells and oxidized into retinaldehyde
- retinaldehyde processed
3 fates of retinaldehyde
- converted to retinoic acids (trxn factors)
- converted to 11-cis-retinaldehyde
- converted back into retinol then back to retinyl esters (for storage, by LRAT and ARAT)
major dietary source of vitamin A is __ which is found in __
major dietary source of vitamin A is retinyl esters which is found in liver, fish, dairy products, eggs
there are over 600 __ in plants, 50 can be metabolized to have __ activity
these are called __
there are over 600 carotenoids in plants, 50 can be metabolized to have vit A activity
these are called pro-vitamin A
provitamin becomes vitamins in the
intestine
main provitamin A carotenoids in human diet are
beta-carotene
alpha-carotene
beta-cryptoxanthin
high content of carotenoids found in
neon foods
carrots
squash
tomatoes
papaya
oranges
leafy greens
top vit A sources in US diet
dairy
eggs
fortified cereals
liver
fish
top sources of provitamin A
carrots
broccoli
cateloupe
squash
carotenoids are/are not vit A
carotenoids are __
carotenoids are/are not vit A
carotenoids are precursors for the synthesis of vit A
carotenoid RDA increases during pregnancy and lactation bc
cell growth
bioavailability: food source and structure of carotenoid affect (4)
- intestinal digestion
- solubilization
- absorption
- metabolism in enterocytes
some carotenoids (ie those in __) are not well absorbed bc
some carotenoids (ie those in spinach) are not well absorbed bc they are trapped in strong food matrix
what helps release carotenoids
cooking
enterocytes absorb and bio-convert 100% of __ into retinol
enterocytes absorb and bio-convert 100% of supp or dietary vit A into retinol
enterocytes absorb and bio-convert 50% of __ into retinol
enterocytes absorb and bio-convert 50% of beta-carotene into retinol
what has worst absorption in enterocyte
dietary beta-carotene
dietary alpha-carotene and beta-cryptoxanthin
dietary/supp __ is effectively absorbed and bio-converted to retinol, but supp/diet __ is less efficiently converted
dietary/supp vit A is effectively absorbed and bio-converted to retinol, but supp/diet pro-vit A (beta-carotene) is less efficiently converted
vit A upper tolerable limit is only __x the DRI
vit A upper tolerable limit is only 2-3 times the DRI
upper limits of vit A cause
- liver abnormalities
- teratogenic effects
- toxic effects in infants and children
should we use beta-carotene and provit A supplements?
no bc of risks of upper limit
4 stages of vit A digestion and absorption
- dietary vit A (retinyl esters) and carotenoids **released from food by proteolysis **in stomach aggregate with lipids
- in small intestine, emulsified with lipids and bile salts, retinyl esters are hydrolyzed by pancreatic lipases: release retinol which will enter the enterocyte
- all-trans retinol in micelles (w/ bile salts) are well-absorbed (70-90%)
- efficiency of beta-carotenoids absorption: 5-65%
absorption of vit A requires dietary
lipids/fats
absorption rate of all-trans retinol micelles
70-90%
absorption rate of beta-carotenoids
5-65%
all forms of vit A in the cell are
carried by protein
digestion and absorption of vit A steps
- ingestion of protein-bound carotenoids and retinyl esters
- proteases (pepsin, trypsin) release vit A vitamers
- hydrolases (esterases, lipases) remove FA from retinyl esters
- free carotenoids and free retinol incorporated into a micelle (requires fat and bile)
- micelle navigates layer of water and goes to membrane
- retinol packaged into chylomicrons and shuttled into lymph
all intracellular vit A vitamers are carried by a __ such as __
all intracellular vit A vitamers are carried by a protein such as CRBPII
most retinol entering the enterocyte is converted into __ and packaged into __, and shuttled through the __ system
most retinol entering the enterocyte is converted into retinyl esters and packaged into chylomicrons, and shuttled through the lymph system
why isn’t vit A directly transported to the liver via portalc circulation
that would overwhelm the liver with fat
how does retinol enter cell?
diffusion, it doesn’t need a trasnporter
