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HUNT241 > Nutrition Lecture 8: Thiamin > Flashcards

Nutrition Lecture 8: Thiamin Flashcards

1
Q

What are rich sources of thiamin?

A

Whole grains, pork, potato skin, fortified wheat-bix and soy milk

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2
Q

What foods cause thiamin losses?

A

Refining grains (e.g. rice, wheat)

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3
Q

What does a ‘thiamin antagonist’ mean?

A

Substances that interfere with the absorption of thiamin

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4
Q

What are examples of thiamin antagonists?

A
  • Sulfites (to preserve colour of meat)
  • Cyanogenic glycosides (in cassava)
  • Tannins (tea, coffee, betel nuts)
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5
Q

What does thiaminases mean?

A

Enzymes that break down thiamin

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6
Q

What are examples of thiaminases?

A
  • Plants such as bracken fern
  • Some kaimoana including carp, mussels
  • Insects including african silk worm larvae
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7
Q

What is betel nut chewing?

A

An important cultural practice in south and south-east Asia, Asia pacific

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8
Q

What are the effects of betel nut chewing?

A

Stimulant drug, addictive

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9
Q

What are the long term affects of betel nut chewing?

A

Discolouration of teeth and gums, mouth ulcers and oral cancers

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10
Q

Is thiamin water soluble?

A

Yes, water soluble, stable in acid solution and when frozen

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11
Q

What is thiamin unstable to?

A

Heat, UV light and alkali

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12
Q

What type of compound is thiamin?

A

Colourless organosulfur compound

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13
Q

What is the chemical structure of thiamin?

A

2 rings and a bridge in-between

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14
Q

What are the names of the two rings that make up thiamin?

A

Aminopyrimidine ring and Thiazolium ring

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15
Q

What is the name of the bridge that connects the two rings that make up thiamin?

A

Methylene bridge

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16
Q

How many phosphorylated forms of thiamin are there?

A

3

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17
Q

What are the three phosphorylated forms of thiamin

A

TMP, TPP, TTP

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18
Q

What does TMP stand for?

A

Thiamin monophosphate

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19
Q

What does TPP stand for?

A

Thiamin diphosphate

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20
Q

What does TTP stand for?

A

Thiamin triphosphate

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21
Q

What can all three forms of thiamin do?

A

All can be interconverted in tissues

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22
Q

What percent of total tissue thiamin is TMP, TPP and TTP?

A
  • 80% is TPP
  • 5-10% is TTP
  • Remainder is TMP
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23
Q

What is the active form of Thiamin?

A

Thiamin pyrophosphate (TPP)

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24
Q

How is thiamin turned into its active form TPP?

A

By the enzyme thiamin diphosphotransferase
- This conversion involves the addition of two phosphate groups to thiamin, utilizing ATP in the process

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25
Q

Where does absorption of thiamin happen?

A

Mainly in the jejunum and ileum

26
Q

What are the two main mechanisms of absorption of thiamin?

A
  • Active carrier-mediated
  • Passive diffusion
27
Q

When does active-carrier mediated process happen?

A

When thiamin is at low concentrations

28
Q

When does passive diffusion occur?

A

When thiamin is at high concentrations

29
Q

What is thiamin released by in the upper small intestine?

A

By phosphatase and pyrophosphatase

30
Q

What is bioavailability of thiamin affected by?

A

Little information, alcohol consumption, absorption increases when intakes are low

31
Q

Where is approximately 90% of thiamin in blood found?

A

In erthrocytes

32
Q

Where is majority of thiamin in plasma found?

A

Mainly bound to proteins, mainly albumin

33
Q

How much thiamin can humans store?

A

approx. 25 to 30mg - can be depleted within 2-3 weeks

34
Q

Where are the highest tissue concentrations of thiamin?

A

Skeletal muscle, heart, brain, liver and kidneys

35
Q

What metabolisms are thiamin important for?

A

Energy metabolism and CHO metabolism (as TPP)

36
Q

What is thiamin required for the activity of?

A
  • Transketolase
  • a-ketoglutarate dehydrogenase
  • pyruvate dehydrogenase
  • branched chain a-keto acid dehydrogenase
37
Q

What is Transketolase?

A

Transketolase is an enzyme that plays a crucial role in the pentose phosphate pathway (PPP)

38
Q

What is the pentose phosphate pathway (PPP)?

A

an alternative glucose metabolic pathway parallel to glycolysis, primarily involved in the production of NADPH and ribose-5-phosphate

39
Q

What is a-ketoglutarate dehydrogenase?

A

an enzyme complex involved in the citric acid cycle

40
Q

What is a-ketoglutarate dehydrogenase responsible for?

A

is responsible for the conversion of α-ketoglutarate to succinyl-CoA

41
Q

What is pyruvate dehydrogenase?

A

pyruvate dehydrogenase is a crucial enzyme complex in cellular respiration

42
Q

What is pyruvate dehydrogenase responsible for?

A

the conversion of pyruvate to acetyl-CoA to enter the CAC

43
Q

What is the branched chain a-keto acid dehydrogenase?

A

complex that helps break down certain types of protein building blocks called branched-chain amino acids (BCAAs)

44
Q

What is branched chain a-keto acid dehydrogenase responsible for?

A

forming Acetyl-CoA derivatives to enter the CAC

45
Q

Consuming what causes risk factors for thiamin deficiency?

A

Thiamin antagonists, thiaminases

46
Q

What disease states are risks for thiamin deficiency?

A

Alcoholism, bariatric surgery

47
Q

What conditions does thiamin deficiency cause?

A

Beriberi, wernickes encephalopathy

48
Q

What is beriberi?

A

“WET” Oedema and cardiac enlargement due to intense vasodilation from accumulation of pyruvate and lactate in blood and tissues

49
Q

What is chronic beriberi?

A

“DRY” Affects peripheral nerves rather than the CV system

50
Q

What is infantile beriberi?

A

Infants < 4 months with non-specific signs

51
Q

What are the symptoms of infantile beriberi?

A

Irritability, refusal to breastfeed, vomiting, piercing cry, then signs of chronic heart failure

52
Q

What is the most common form of thiamin deficiency in adults and older children?

A

Wernickes encephalopathy

53
Q

What does wernickes encephalopathy affect?

A

Cerebellum and brain stem

54
Q

What is the most severe form of wernickes encephalopathy?

A

Korsakoff’s psychosis

55
Q

What is Korsakoff’s psychosis?

A

amnesia, confusion, confabulation, little working memory

56
Q

What are symptoms of milk thiamin deficiency?

A

Sleeplessness, depression, weight loss, fatigue and irritability

57
Q

What are stratagies to improve thiamin status?

A

Rice and wheat flour fortification with thiamin

58
Q

What is the EAR for thiamin?

A

Men = 1.0mg/day
Women = 0.9mg/day

59
Q

What is the RDI for thiamin?

A

Men = 1.0mg/day
Women = 1.1mg/day

60
Q

What is the upper level of intake for thiamin?

A

No upper level of intake set

HUNT241 (22 decks)

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