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NTDT401 > Thiamin > Flashcards

Thiamin Flashcards

1
Q

What reaction requires pyruvate dehydrogenase (PDH)

A

pyruvate to acetyl CoA

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2
Q

What reaction requires a-ketoglutarate dehydrogenase (a-KG D)

A

a-ketoglutarate to succinyl CoA

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3
Q

Structure: explain the methylene bridge

A

CH2 linking the pyrimidine ring and thiazole

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4
Q

Describe thiamin structure

A

pyrimidine ring, thiazole, sulfur-containing, phosphorylation

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5
Q

Which form of thiamin phosphate is the active coenzyme form

A

thiamin diphosphate / thiamin pyrophosphate (TDP OR TPP)

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6
Q

Why is TDP unable to be transported through the cell membrane?

A

interaction of -P and phospholipid bilayer

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7
Q

How is TDP formed

A

Thiamin–(ATP + thiamin pyrophosphokinase)_>TDP/TPP

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8
Q

Define coenzyme

A

vitamin based/ organic; aids in enzyme function-not always reusable

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9
Q

cofactors

A

mineral-based

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10
Q

What are good sources of thiamin

A

pork, whole or enriched grains, legumes, watermelon

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11
Q

How is thiamin stored in plants

A

free form

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12
Q

How does thiamin exist in animal products

A

TDP

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13
Q

How is free form thiamin digested

A

form is already able to be utilized; is absorbed

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14
Q

How is TDP digested

A

requires dephosphorization as TDP is unusable; intestinal phosphatase remove P prior to absorption

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15
Q

Bioavailability

A

high except when present wit anti-thiamin factors

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16
Q

what are anti-thiamin factors

A

thiaminases and inhibitors

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17
Q

Thiaminases

A

destroy the bridge; present in raw fish and some F+V

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18
Q

what inhibit thiamin

A

tea, coffee

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19
Q

is absorption active or passive

A

BOTH (depends on quantity)

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20
Q

When is active transport used

A

intakes less than 5mg/d

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21
Q

When is passive transport used

A

higher intakes

22
Q

How is thiamin moved from GI to blood

A

transport from the mucosal cell across the basolateral membrane

23
Q

what may interfere with absorption

A

ethanol

24
Q

Where are sites of thiamin

A

within enterocyte, in circulation (TMP, majority in RBC), major organs

25
Q

What is thiamin needed for

A

energy release and transformation

26
Q

Explain energy release and transformation

A

TDP functions as a coenzyme for oxidative decarboxylation of pyrute and a-KG

27
Q

What would inhibition of this coenzyme cause

A

build up in pyruvate, lactate, and a-KG

28
Q

how many ATP does NADH create

A

3

29
Q

how many ATP does FAHD2 create

A

2

30
Q

Describe pyruvate dehydrogenase

A

large complex with multiple copies of 3 enzymes: E1, E2, and E3

31
Q

E1 subunit

A

pyruvate dehydrogenase; 30 copies; Prosthetic: TPP

32
Q

E2 subunit

A

dihydrolipoyl transacetylase, 60 copies, Prosthetic: lipoamide

33
Q

E3 subunity

A

dihydrolipoyl dehydrogenase; 12 copies; Prosthetic: FAD

34
Q

What inhibits PDC

A

NADH and Acetyl CoA

35
Q

PDH Complex Mechanism step 1

A

CO2 is removed from pyruvate and rest of compound attaches to TDP

36
Q

PDH complex step 2

A

hydroxyethyl group transferred to oxidized lipoamide–> generates acetyl lipoamide

37
Q

PDH complex step 3

A

acetyl lipoamide reacts with CoA to form acetyl CoA

38
Q

PDH complex step 4

A

reduce lipoamide is oxidized by FAD dependent enzyme dihydrolipoyl dehydrogenase

39
Q

PDH complex step 5

A

reduced protein (FADH2) is oxidized by NAD

40
Q

function: Decarboxylation

A

TDP required for alpha KG to form succinyl CoA; also used for branched-chain alpha ketoacids

41
Q

Decarboxylation of branch-chain alpha keto acids

A

require TDP; failure results in accumulation of BC alpha keto and BCAA

42
Q

Synthesis of NADPH and Pentoses

A

TDP coenzyme for transketolase; key enzyme in hexose monophosphate shunt (sugars of varying lengths are interconverted

43
Q

how is thiamin excreted

A

excess metabolized for urinary excretion

44
Q

Degradation

A

cleavage of molecule into pyrimidine and thiazole moieties

45
Q

Thiamin DRI/RDA

A

1.1-1.2mg/d (increase to 1.4-1.5 in pregnancy); no UL

46
Q

Thiamin Deficiency

A

Beriberi (dry/wet/acute): wasting and muscle weakness

47
Q

Wernicke’s Encephalopathy

A

mental confusion, memory loss, unsteady gait–> seen mostly in alcoholics due to liver damage

48
Q

Deficiency is observed in what groups

A

elderly, impaired absorption, stomach surgery pts, alcoholism

49
Q

When is toxicity seen

A

excessive thiamin administered by IV

50
Q

Assessment: test used

A

Transketolase Stimulation Test

NTDT401 (20 decks)

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