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IHN: Biochemistry 2 > Vitamin A and Carotenoids > Flashcards

Vitamin A and Carotenoids Flashcards

1
Q

retinoids comprise both __ and __ species that bear a structural resemblance to __, with or without the biological activity of __

A

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

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2
Q

main function of Vitamin A

A

growth factor at all stages in life

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3
Q

6 biological functions of vitamin A

A
  1. bone formation
  2. vision
  3. immune
  4. cell growth and differentiation
  5. reproduction
  6. organ development
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4
Q

In cell growth and differentiation, vitamin A becomes a __ that affects a large number of genes

A

In cell growth and differentiation, vitamin A becomes a transcription that affects a large number of genes

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5
Q

vitamin A is a subgroup of __

A

vitamin A is a subgroup of retinoids

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6
Q

biologically active form of vitamin A

A

all-trans retinol

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7
Q

storage form of Vitamin A

A

retinyl-esters

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8
Q

transport form of Vit A

A

all-trans retinol

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9
Q

all-trans retinol

A
  1. transport form of Vit A
  2. substrate for making biologically active Vit A
  3. active form of Vit A, bc it is the precursor
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10
Q

oxidation of all-trans-retinol produces __ which is transported into __ and used in several __

A

oxidation of all-trans-retinol produces all-trans-retinal which is transported into cells and used in several biological pathways

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11
Q

all-trans retinoic acid requireds __ to be a __ factor derived from __

A

all-trans retinoic acid requires 9-cis-retinoic acid to be a transcription factor derived from Vit A

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12
Q

retinyl ester = retinol + __

A

retinyl ester = retinol + fatty acid (FA)

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13
Q

retinyl esters are the __ form of vitamin A stored primarily in the __

A

retinyl esters are the storage form of vitamin A stored primarily in the liver

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14
Q

retinyl-esters are the __ form of Vitamin A in __

A

retinyl-esters are the transportable form of Vitamin A in chylomicrons

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15
Q

11-cis-retinal is a __ factor that controls __ and is necessary for formation of __

A

11-cis-retinal is a transcription factor that controls nocturnal vision and is necessary for formation of rhodopsin

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16
Q

13-cis-retinoic acid aka __ is a __ __ factor and is a more __ form of retinoic acid

A

13-cis-retinoic acid aka accutane is a synthetic transcription factor and is a more potent/active form of retinoic acid

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17
Q

carotenoid structure

A

2 retinal attached

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18
Q

3 most abundant carotenoids

A
  1. beta-carotene
  2. alpha-carotene
  3. lycopene
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19
Q

__ and __ can be converted into trans-retinal

A

beta-carotene and alpha-carotene can be converted into trans-retinal

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20
Q

lycopene is a __, but can’t be converted to __

A

lycopene is a essential antioxidant, but can’t be converted to vit A

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21
Q

where do animals get carotenoids?

A

diet, we can’t make them de novo

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22
Q

2 chemical forms of carotenoids

A
  1. carotenes
  2. xantophylls
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23
Q

carotenes are made of __ and __ and include __, __, and __

A

carotenes are made of hydrogen and carbon and include beta and, alpha-carotene, and lycopene

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24
Q

xantophylls have at least one __ and include __ and __

A

xantophylls have at least one oxygen and include beta and alpha-crypyoxanthin

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25
Q

pro-vitamin definition

A

substance that can be converted to a vitamin

26
Q

Provitamin A

A
  1. beta-carotene
  2. alpha-carotene
  3. beta-cryptoxanthin
  4. alpha-cryptoxanthin
27
Q

non-provitamin A

A
  1. lycopene
  2. zeaxanthing
  3. lutein
28
Q

main food form of vitamin A

A

retinyl esters

29
Q

2 enzymes that promote synthesis of retinyl esters

A

LRAT and ARAT

30
Q

retinoid metabolism steps overview

A
  1. retinyl esters obtained from diet
  2. retinyl esters to retinol
  3. retinol transported into cells and oxidized into retinaldehyde
  4. retinaldehyde processed
31
Q

3 fates of retinaldehyde

A
  1. converted to retinoic acids (trxn factors)
  2. converted to 11-cis-retinaldehyde
  3. converted back into retinol then back to retinyl esters (for storage, by LRAT and ARAT)
32
Q

major dietary source of vitamin A is __ which is found in __

A

major dietary source of vitamin A is retinyl esters which is found in liver, fish, dairy products, eggs

33
Q

there are over 600 __ in plants, 50 can be metabolized to have __ activity
these are called __

A

there are over 600 carotenoids in plants, 50 can be metabolized to have vit A activity
these are called pro-vitamin A

34
Q

provitamin becomes vitamins in the

A

intestine

35
Q

main provitamin A carotenoids in human diet are

A

beta-carotene
alpha-carotene
beta-cryptoxanthin

36
Q

high content of carotenoids found in

A

neon foods
carrots
squash
tomatoes
papaya
oranges
leafy greens

37
Q

top vit A sources in US diet

A

dairy
eggs
fortified cereals
liver
fish

38
Q

top sources of provitamin A

A

carrots
broccoli
cateloupe
squash

39
Q

carotenoids are/are not vit A
carotenoids are __

A

carotenoids are/are not vit A
carotenoids are precursors for the synthesis of vit A

40
Q

carotenoid RDA increases during pregnancy and lactation bc

A

cell growth

41
Q

bioavailability: food source and structure of carotenoid affect (4)

A
  1. intestinal digestion
  2. solubilization
  3. absorption
  4. metabolism in enterocytes
42
Q

some carotenoids (ie those in __) are not well absorbed bc

A

some carotenoids (ie those in spinach) are not well absorbed bc they are trapped in strong food matrix

43
Q

what helps release carotenoids

A

cooking

44
Q

enterocytes absorb and bio-convert 100% of __ into retinol

A

enterocytes absorb and bio-convert 100% of supp or dietary vit A into retinol

45
Q

enterocytes absorb and bio-convert 50% of __ into retinol

A

enterocytes absorb and bio-convert 50% of beta-carotene into retinol

46
Q

what has worst absorption in enterocyte

A

dietary beta-carotene
dietary alpha-carotene and beta-cryptoxanthin

47
Q

dietary/supp __ is effectively absorbed and bio-converted to retinol, but supp/diet __ is less efficiently converted

A

dietary/supp vit A is effectively absorbed and bio-converted to retinol, but supp/diet pro-vit A (beta-carotene) is less efficiently converted

48
Q

vit A upper tolerable limit is only __x the DRI

A

vit A upper tolerable limit is only 2-3 times the DRI

49
Q

upper limits of vit A cause

A
  1. liver abnormalities
  2. teratogenic effects
  3. toxic effects in infants and children
50
Q

should we use beta-carotene and provit A supplements?

A

no bc of risks of upper limit

51
Q

4 stages of vit A digestion and absorption

A
  1. dietary vit A (retinyl esters) and carotenoids **released from food by proteolysis **in stomach aggregate with lipids
  2. in small intestine, emulsified with lipids and bile salts, retinyl esters are hydrolyzed by pancreatic lipases: release retinol which will enter the enterocyte
  3. all-trans retinol in micelles (w/ bile salts) are well-absorbed (70-90%)
  4. efficiency of beta-carotenoids absorption: 5-65%
52
Q

absorption of vit A requires dietary

A

lipids/fats

53
Q

absorption rate of all-trans retinol micelles

A

70-90%

54
Q

absorption rate of beta-carotenoids

A

5-65%

55
Q

all forms of vit A in the cell are

A

carried by protein

56
Q

digestion and absorption of vit A steps

A
  1. ingestion of protein-bound carotenoids and retinyl esters
  2. proteases (pepsin, trypsin) release vit A vitamers
  3. hydrolases (esterases, lipases) remove FA from retinyl esters
  4. free carotenoids and free retinol incorporated into a micelle (requires fat and bile)
  5. micelle navigates layer of water and goes to membrane
  6. retinol packaged into chylomicrons and shuttled into lymph
57
Q

all intracellular vit A vitamers are carried by a __ such as __

A

all intracellular vit A vitamers are carried by a protein such as CRBPII

58
Q

most retinol entering the enterocyte is converted into __ and packaged into __, and shuttled through the __ system

A

most retinol entering the enterocyte is converted into retinyl esters and packaged into chylomicrons, and shuttled through the lymph system

59
Q

why isn’t vit A directly transported to the liver via portalc circulation

A

that would overwhelm the liver with fat

60
Q

how does retinol enter cell?

A

diffusion, it doesn’t need a trasnporter

IHN: Biochemistry 2 (38 decks)

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