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IHN: Biochemistry 2 > Niacin > Flashcards

Niacin Flashcards

1
Q

niacin, thiamin, and riboflavin are needed in __ amounts

A

niacin, thiamin, and riboflavin are needed in very small amounts

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2
Q

4 general aspects of niacin, thiamin, and riboflavin

A
  1. variable heat-resistance. alkaline-labile, sensitive to light
  2. present in most food sources
  3. excreted mainly through urine
  4. deficiency is rare in developed countries, but certain groups are at risk
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3
Q

why does heat resistance of vitamins matter

A

we need to know what cooking provess is appropriate

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4
Q

how are niacin, thiamin, and riboflavin excreted

A

urine

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5
Q

niacin aka

A

NIcotinic ACid vitamIN

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6
Q

niacin refers to

A

nicotinic acid (niacin) AND nicotinamide (niacinamide)

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7
Q

niacin aka

A

nicotnic acid

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8
Q

niacinamide aka

A

nicotinamide

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9
Q

main function of niacin

A

precursor for NAD and NADP

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10
Q

NAD and NADP are __ molecules

A

NAD and NADP are oxidizing molecules

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11
Q

active niacin can be made from

A
  1. tryptophan
  2. nicotnic acid
  3. nicotinamide
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12
Q

humans can synthesize niacin from

A

tryptophan

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13
Q

if we have enough __, we may not need to consume niacin, BUT __

A

if we have enough tryptophan, we may not need to consume niacin, BUT it is hard to consume that much Trp

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14
Q

which of these foods contain niacin?

A

ALL OF THE ABOVE

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15
Q

foods with high niacin content

A
  • meats
  • poultry
  • fish
  • legumes
  • peanuts
  • cereals
  • enriched flours and cereals
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16
Q

what forms of niacin can enterocyte absorb directly?

A

nicotinamide and nicotinic acid

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17
Q

NAD+ and NADP absorption into enterocyte

A

CAN’T be directly absorbed
must be broken down and reassembled

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18
Q

niacin is found mostly in __ bound forms __ and __

A

niacin is found mostly in covalently bound forms NAD+ and NADP

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19
Q

niacin in __ is naturally NOT bioavailable

A

niacin in grains (bran) is naturally NOT bioavailable

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20
Q

1 mg niacin = __ mg tryptophan (~_ g good quality protein)

A

1 mg niacin = 60 mg tryptophan (~6 g good quality protein)

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21
Q

the average US diet contains enough __ for niacin requirement through synthesis of __

A

the average US diet contains enough protein for niacin requirement through synthesis of tryptophan

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22
Q

at low conc, niacin is absorbed via

A

carrier-mediated, Na-dependent facilitated diffusion

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23
Q

where is glycohydrolase found?

A

all cells

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24
Q

shortcut for NAD/NADP degradation

A

glycohydrolase turns NAD and NADP directly into nicotinamide

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25
Q

steps of niacin absorption

A
  1. NAD, NADP –> NMN (enzyme: phosphatase)
  2. NMN –> nicotinamide riboside (enzyme: phosphatase)
  3. nicotinamide riboside –> nicotinamide (hydratase)
  4. nicotinamide absorbed into enterocyte
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26
Q

de novo pathway diversion

A

ACMS to AMS (by ACMSD) to acetyl-CoA

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27
Q

de novo pathway steps

A

tryptophan –> ACMS –> NAD

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28
Q

what happens to the following once they enter the enterocyte:
NMN
nicotinamide
nicotnic acid

A

ALL enter portal circulation (mainly nicotinamide) (NMN as NAD) and go to liver
liver distributes to rest of body

29
Q

at high conc, niacin is absorbed via

A

passive diffusion

30
Q

NAD+ is synthesized by 3 pathways

A
  1. de novo pathway
  2. Preiss-Handler pathway
  3. Salvage pathway
31
Q

where is de novo pathway most active?

A

liver and kidney

32
Q

which organ uses all 3 pathways?

A

the liver

33
Q

preiss-handler converts

A

nicotinic acid to NAD+

34
Q

high fat, high leucine diet, and diabetic ketoacidosis __ niacin synthesis by inducing __

A

high fat, high leucine diet, and diabetic ketoacidosis reduce niacin synthesis by inducing ACMSD

35
Q

preiss-handler requires a lot of __ and is only used when there is __

A

preiss-handler requires a lot of energy and is only used when there is excess

36
Q

salvage pathway recycles __ to yield __ and is used by __

A

salvage pathway recycles NADP to yield nicotinamide and is used by sirtuins (SIRT)

37
Q

people deficient in __, __, and __ will be niacin deficient bc __

A

people deficient in iron, riboflavin, and vit B6 will be niacin deficient bc they are all required to synthesize NAD

38
Q

what enzyme diverts synthesis of NAD to acetyl-CoA?

A

ACMSD

39
Q

liver uptakes __, __, and __ and converts them to NAD

A

liver uptakes nicotinamide, nicotnic acid, and tryptophan and converts them to NAD

40
Q

what enzyme converts NAD+ to nicotinamide

A

NAD+ glycohydrolase

41
Q

can the liver store NAD?

A

yes, but just some

42
Q

main niacin form in blood

A

nicotinamide

43
Q

degradation of niacin in liver
nicotinamide is __ to __
nicotinic acid is __ to __
untransformed niacin found during __

A

degradation of niacin in liver
nicotinamide is methylated to N1-methyl-nicotinamide
nicotinic acid is conjugated to nicotinuric acid
untransformed niacin found during high niacin diet

44
Q

tissues rapidly convert nicotinamide and nicotinic acid to __ and __

A

tissues rapidly convert nicotinamide and nicotinic acid to NAD and NADP

45
Q

NAD pool is mostly __ due to ETC activity

A

NAD pool is mostly NAD+ due to ETC activity

46
Q

NADP pool is mostly __ due to PPP

A

NADP pool is mostly NADPH due to PPP

47
Q

NAD can function as a __ or __

A

NAD can function as a coenzyme or substrate

48
Q

NAD as a coenzyme
__ and __ are electron acceptors of hydrogen donors in rxns

A

NAD as a coenzyme
NAD and NADP are electron acceptors of hydrogen donors in rxns

49
Q

NAD as a substrate
__ acts as a donor of ADP-ribose for __ modification of proteins

A

NAD as a substrate
NAD+ acts as a donor of ADP-ribose for posttranslational modification of proteins

50
Q

PARPs create more __ chromatin

A

PARPs create more relaxed chromatin

51
Q

sirtuins (SIRT) create more __ chromatin

A

sirtuins (SIRT) create more condensed chromatin

52
Q

what kind of enzyme are SIRTs?
what do they do to chromatin?

A

deacetylases
condense chromatin

53
Q

PARPs and SIRTs turn __ to __

A

PARPs and SIRTs turn NAD+ to nicotinamide

54
Q

2 sources of substrate for ADP-ribosylation of proteins or acetyl groups
__ is released in reaction

A
  1. PARP
  2. Sirtuins (SIRT)
    nicotinamide is released in reaction
55
Q

why do NAD+ levels oscillate in a circadian fashion?

A

differential expression of NAMPT (rate-limiting enzyme in NAD salvage pathway)
affects SIRTs

56
Q

NAD+ levels oscillate in __ fashion in all cell types

A

NAD+ levels oscillate in circadian fashion in all cell types

57
Q

how to determine niacin status?

A

urinary excretion of niacin metabolites

58
Q

determining niacin status: look at

A

ratio btwn NMN (substrate) and its oxidized product

59
Q

niacin deficiency

A

Pellagra

60
Q

pellgra symptoms

A

4 Ds
diarrhea, dermatitis, dementia, death

61
Q

people at risk for Pellagra

A
  1. low protein
  2. aloholics
  3. cancer
  4. genetic disorder
62
Q

pellagra is seasonal bc

A

sun-exposed skin more commonly has rash
sunlight breaks down DNA, no way to repair without niacin

63
Q

can we store niacin

A

no

64
Q

what is the only water soluble vitamin we can store

A

B12

65
Q

Hartnup disease is a mutation in the __ transporter

A

Hartnup disease is a mutation in the tryptophan transporter

66
Q

Hartnup disease

A
  1. autosomal recessive disorder
  2. mutation in SLCA19 gene
  3. defective transport of tryptophan
  4. manifests like Pellagra
67
Q

how to treat Hartnup disease?

A

niacin pills, high protein diet, avoid sun

68
Q

niacin can also be used to treat

A

artherosclerosis

69
Q

niacin is vitamin

A

B3

IHN: Biochemistry 2 (38 decks)

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