Thiamin

Question 1

What reaction requires pyruvate dehydrogenase (PDH)

Answer 1

pyruvate to acetyl CoA

Question 2

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

Answer 2

a-ketoglutarate to succinyl CoA

Question 3

Structure: explain the methylene bridge

Answer 3

CH2 linking the pyrimidine ring and thiazole

Question 4

Describe thiamin structure

Answer 4

pyrimidine ring, thiazole, sulfur-containing, phosphorylation

Question 5

Which form of thiamin phosphate is the active coenzyme form

Answer 5

thiamin diphosphate / thiamin pyrophosphate (TDP OR TPP)

Question 6

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

Answer 6

interaction of -P and phospholipid bilayer

Question 7

How is TDP formed

Answer 7

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

Question 8

Define coenzyme

Answer 8

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

Question 9

cofactors

Answer 9

mineral-based

Question 10

What are good sources of thiamin

Answer 10

pork, whole or enriched grains, legumes, watermelon

Question 11

How is thiamin stored in plants

Answer 11

free form

Question 12

How does thiamin exist in animal products

Answer 12

TDP

Question 13

How is free form thiamin digested

Answer 13

form is already able to be utilized; is absorbed

Question 14

How is TDP digested

Answer 14

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

Question 15

Bioavailability

Answer 15

high except when present wit anti-thiamin factors

Question 16

what are anti-thiamin factors

Answer 16

thiaminases and inhibitors

Question 17

Thiaminases

Answer 17

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

Question 18

what inhibit thiamin

Answer 18

tea, coffee

Question 19

is absorption active or passive

Answer 19

BOTH (depends on quantity)

Question 20

When is active transport used

Answer 20

intakes less than 5mg/d

Question 21

When is passive transport used

Answer 21

higher intakes

Question 22

How is thiamin moved from GI to blood

Answer 22

transport from the mucosal cell across the basolateral membrane

Question 23

what may interfere with absorption

Answer 23

ethanol

Question 24

Where are sites of thiamin

Answer 24

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

Question 25

What is thiamin needed for

Answer 25

energy release and transformation

Question 26

Explain energy release and transformation

Answer 26

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

Question 27

What would inhibition of this coenzyme cause

Answer 27

build up in pyruvate, lactate, and a-KG

Question 28

how many ATP does NADH create

Answer 28

3

Question 29

how many ATP does FAHD2 create

Answer 29

2

Question 30

Describe pyruvate dehydrogenase

Answer 30

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

Question 31

E1 subunit

Answer 31

pyruvate dehydrogenase; 30 copies; Prosthetic: TPP

Question 32

E2 subunit

Answer 32

dihydrolipoyl transacetylase, 60 copies, Prosthetic: lipoamide

Question 33

E3 subunity

Answer 33

dihydrolipoyl dehydrogenase; 12 copies; Prosthetic: FAD

Question 34

What inhibits PDC

Answer 34

NADH and Acetyl CoA

Question 35

PDH Complex Mechanism step 1

Answer 35

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

Question 36

PDH complex step 2

Answer 36

hydroxyethyl group transferred to oxidized lipoamide--> generates acetyl lipoamide

Question 37

PDH complex step 3

Answer 37

acetyl lipoamide reacts with CoA to form acetyl CoA

Question 38

PDH complex step 4

Answer 38

reduce lipoamide is oxidized by FAD dependent enzyme dihydrolipoyl dehydrogenase

Question 39

PDH complex step 5

Answer 39

reduced protein (FADH2) is oxidized by NAD

Question 40

function: Decarboxylation

Answer 40

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

Question 41

Decarboxylation of branch-chain alpha keto acids

Answer 41

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

Question 42

Synthesis of NADPH and Pentoses

Answer 42

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

Question 43

how is thiamin excreted

Answer 43

excess metabolized for urinary excretion

Question 44

Degradation

Answer 44

cleavage of molecule into pyrimidine and thiazole moieties

Question 45

Thiamin DRI/RDA

Answer 45

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

Question 46

Thiamin Deficiency

Answer 46

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

Question 47

Wernicke's Encephalopathy

Answer 47

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

Question 48

Deficiency is observed in what groups

Answer 48

elderly, impaired absorption, stomach surgery pts, alcoholism

Question 49

When is toxicity seen

Answer 49

excessive thiamin administered by IV

Question 50

Assessment: test used

Answer 50

Transketolase Stimulation Test