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Biochemistry > Fat-Soluble Vitamins > Flashcards

Fat-Soluble Vitamins Flashcards

1
Q

What are the 3 vitamins (active forms) of vitamin A

A

retinal, retinol, retinoic acid

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2
Q

What cleaves beta carotene into retinol and retinal

A

the brush border enzyme dioxygenase

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3
Q

Why is only 1 mg of Vit A derived from 6mg of beta carotene

A

Dioxygenase doesn’t always cleave beta carotene perfectly, so discards the short strand and trims the long one

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4
Q

is beta carotene or Vit A stored in the body

A

Beta carotene is stored in fat (making it yellow), Vit A is predominately stored in the ITO cells of the liver

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5
Q

What is the storage form of Vit A

A

retinol esters with fatty acids

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6
Q

What is the role of retinoic acid

A

Acts like a lipid soluble hormone

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7
Q

How are isoprenes formed

A

via the mevalonic acid pathway

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8
Q

How does Vit A get to cells

A

via chylomicrons

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9
Q

Where is 11-cis retinal used

A

it’s a component of rhodopsin

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10
Q

What is transthyretin

A

protein that carries thyroid hormones and also binds to retinol-RBP complex

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11
Q

Why is it significant that transthyretin bind to the retinol-RBP complex

A

Because it would be filtered out of the blood by the kidney but transthyretin prevents this

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12
Q

What happens to a basal cell if it receives copious Vit A

A

It grows up to be cuboidal, columnar, or goblet cell

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13
Q

What happens to a basal cell if it receives little Vit A

A

It grows up to be squamous (keratinized)

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14
Q

How many genes are regulated by Vit A

A

possibly 500 different ones

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15
Q

How does Vit A affect genes

A

It binds to a RAR: retinoic acid receptor

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16
Q

What is a homodimeric RAR

A

2 receptors both bind vit A and then act as a unit of DNA

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17
Q

What is a heterodimeric RAR

A

One half binds Vit A, the other binds Thyroid hormone, Vit D, prostaglandin, etc

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18
Q

Where does cholecalciferol come from

A

formed from the action of UV light (297nm) on 7-dehydrocholesterol

19
Q

What layers of the skin make cholecalciferol

A

stratum spinosum and basal layers

20
Q

How do the liver and kidney hydroxylate Vit D precursors

A

They use CYP27A and CYP27B, respectively (phase 1 metabolism)

21
Q

How is Vit D absorbed from the GI tract

A

It is absorbed like a fat, via bile salt emulsification etc

22
Q

What is Vit D synthesis in the skin contingent upon

A

Temperature and melanin

23
Q

What’s the half life of cholecalciferol (Vit D from skin)

A

36-72 hours

24
Q

What’s the half life of 25-hydroxycholecalciferol (Vit D from liver)

A

15 days

25
Q

What’s the half life of 1,25-dihydroxycholecalciferol (Vit D from kidneys)

A

4-15 hours

26
Q

How many genes are targeted by Vit D

A

200-3,000

27
Q

how many receptor types are there for Vit D

A

35

28
Q

how many tissues make Vit D

A

17

29
Q

What is the role of Vit E in the body`

A

Prevents free radical damage in polyunsaturated fats

30
Q

Where can Vit E be found

A

It is a membrane associated vitamin

31
Q

How is Vit E metabolized

A

It is not metabolized

32
Q

What is the scientific name of Vit E

A

Vit E is a mix of Tocopherols and tocotrienols; alpha tocopherol is best

33
Q

What is the scientific name of Vit K

A

Menaquinone = K2, phylloquinone = K1

34
Q

What’s the structural difference between K1 and K2

A

K1 isoprene tail is saturated, K2 is unsaturated

35
Q

How are subsets of Vit K2 named

A

With MK- and a number to designate the number of isoprene units in the tail

36
Q

Which Vit K2 subsets are favored by the body

A

MK-4, MK-7

37
Q

What is our main source of Vit K

A

Dietary; it is absorbed as fats are

38
Q

What is the head unit of Vit K called

A

2-methyl-1,4-napthoquinone

39
Q

What is Vit K’s traditionally understood role in the body

A

It is a cofactor in the carboxylation of clotting factors: proteins C, S, Z, and factors II, VII, IX, X

40
Q

Why are infants at increased risk for Vit K deficiency

A

They have low vitamin K stores at birth, vitamin K passes the placenta poorly, the levels of vitamin K in breast milk are low and the gut flora has not yet been developed

41
Q

How does Vit K affect Calcium

A

It utilizes and regulates calcium action; uses osteocalcin and matrix GLA protein to do this

42
Q

What is osteocalcin

A

protein in bone matrix involved in capturing and depositing Ca2+ in bone

43
Q

What is matrix GLA protein

A

Protein in blood vessels that inhibits calcification of soft tissue

Biochemistry (4 decks)

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