Thiamin: Vitamin B1

Question 1

thiamin rich foods

Answer 1

grains, proteins, legumes, fruits

Question 2

active form of thiamin

Answer 2

thiamin pyrophosphate (diphosphate, TPP) or TDP

Question 3

thiamin has __ activity

Answer 3

thiamin has co-factor activity

Question 4

thiamin is very stable in __
unstable in __ and __

Answer 4

thiamin is very stable in acid
unstable in base and UV light

Question 5

thiamin binds __ and converts to __ form

Answer 5

thiamin binds keto-sugar and converts to CoA form

Question 6

most important biological form of thiamin:

Answer 6

TPP or TDP bc of its co-factor activity

Question 7

thiamin is destroyed by __ and __

Answer 7

thiamin is destroyed by alkali (pH > 8) and by prolonged heat

Question 8

__, __, and __ consumption can decrease thiamin availability

Answer 8

raw fish, heme-containing meats, and coffee/tea consumption can decrease thiamin availability

Question 9

thiaminases exist in __ and function to __

Answer 9

thiaminases exist in 2 isoforms and function to cleave thiamin at methylene bridge

Question 10

thiaminases are __ and inactivated with __

Answer 10

thiaminases are thermolabile and inactivated with cooking

Question 11

which thiaminase is more common?

Answer 11

thiaminase 1

Question 12

thiaminase 1 is mainly present in

Answer 12

freshwater fish and shellfish

Question 13

thiaminase II is present in

Answer 13

some bacteria and yeast

Question 14

raw fish contains __ that destroy __

Answer 14

raw fish contains thiaminases that destroy thiamin

Question 15

OCT aka

Answer 15

organic cation transporter

Question 16

absorption of thiamin at physiological concentrations: __
inhibited by __

Answer 16

absorption of thiamin at physiological concentrations: Th-Tr mediated
inhibited by alcohol

Question 17

absorption of thiamin at high concentrations:

Answer 17

passive diffusion

Question 18

2 main thiamin transporters:

Answer 18

ThTr1 and ThTr2

Question 19

ThTr1 and ThTr2 are __
they exchange thiamin for __
greatest activity in __

Answer 19

ThTr1 and ThTr2 are antiporters
they exchange thiamin for H+ ions
greatest activity in upper jejunum

Question 20

ThTr1 expression and capacity

Answer 20

highly expressed in all cells
high capacity

Question 21

ThTr2 expression and capacity

Answer 21

low capacity, high specificty for thiamin
expression increases in response to LOW thiamin intake

Question 22

main form of thiamin in portal circulation

Answer 22

free thiamin

Question 23

thiamin release into circulation

Answer 23

1. ThTr2 on basal side of enterocyte pushes thiamin to basal side
2. free thiamin goes into portal circulation

Question 24

thiamin absorption

Answer 24

1. TMP, TDP to free thiamin (alkaline phosphatase)
2. ThTr1 and 2 on apical surface of enterocyte absorb thiamin

Question 25

organic cation transporters (OCT) may transport __ thiamin in __

Answer 25

organic cation transporters (OCT) may transport **free** thiamin in **intestine**

Question 26

Defects in __ gene which encodes ThTr1 causes a thiamin responseive deficiency disorder, known as __

Answer 26

Defects in **SLC19A2** gene which encodes ThTr1 causes a thiamin responseive deficiency disorder, known as **Rogers syndrome**

Question 27

Rogers syndrome, what transporter still works? is it enough?

Answer 27

ThTr2 but it is not enough to do the work of both

Question 28

~90% thiamin in circulation is in __ as __

Answer 28

~90% thiamin in circulation is in **blood cells** as **TDP**

Question 29

thiamin enters red blood cells by

Answer 29

facilitated diffusion

Question 30

in peripheral tissues, transport into cells mediated by __ (__) and __ (__)

Answer 30

in peripheral tissues, transport into cells mediated by **ThTr1** (**free thiamin**) and **RFC-1** (**uptakes TMP, also reduced folate carriers**)

Question 31

mutations in ThTr1 (Rogers syndrome) is characterized by __, __, and __ repsonsive to __

Answer 31

mutations in ThTr1 (Rogers syndrome) is characterized by **megaloblastic anemia**, **sensorineural deafness**, and **diabetes** repsonsive to **thiamin treatment**

Question 32

thiamin is stored mostly in (5)

Answer 32

1. liver 2. skeletal muscle 3. heart 4. kidney 5. brain these are high energy tissues, thiamin deficiency = low energy

Question 33

50% of body's thiamin is in

Answer 33

muscle

Question 34

is we consume no thiamin, we notice in __

Answer 34

is we consume no thiamin, we notice in **a few weeks**

Question 35

2 types of TDP dependent rxns

Answer 35

1. decarboxylation of alpha-ketoacids to acyl-CoA 2. interconversion of sugar phosphates

Question 36

3 decarboxylation rxns requiring TDP

Answer 36

1. pyruvate dehydrogenase (TCA) 2. alpha-KG dehydrogenase (TCA) 3. branched-chain amino acid dehydrogenase

Question 37

1 interconversion of sugar phosphates rxn

Answer 37

1. transketolase (PPP)

Question 38

TDP-depdendent rxns create __ and __ equivalents for macromolecule synthesis

Answer 38

TDP-depdendent rxns create **energy: ATP** and **reducing** equivalents for macromolecule synthesis

Question 39

inhibition of the TDP requiring rxns leads to accumulation of pyruvate, lactate, and alpha-KG, leading to __

Answer 39

inhibition of the TDP requiring rxns leads to accumulation of pyruvate, lactate, and alpha-KG, leading to **acidosis**

Question 40

determining thiamin status

Answer 40

measure RBC transketolase

Question 41

excess __ causes thiamin deficiency

Answer 41

excess **glucose** causes thiamin deficiency

Question 42

why does excess glucose cause thiamin deficiency?

Answer 42

thiamin follows glucose SO, we supplement thiamin with IV glucose

Question 43

__ inhibits both thiamin transporters

Answer 43

alcohol

Question 44

groups at risk for thiamin deficiency

Answer 44

1. elderly 2. malabsorption 3. alcohol (Wernicke-Korsakoff syndrome) 4. cancer patients undergoing chemo 5. excess glucose infusion 6. congestive heart failure

Question 45

why does excess glucose infusion put you at risk for low thiamin?

Answer 45

thiamin follows glucose thiamin is involved in rxns that produce glucose

Question 46

thiamian deficiency

Answer 46

1. beri beri 2. Wernicke-Korsakoff

Question 47

dry beri beri

Answer 47

chronic neuropathies caused by inactivity + calorie restriction + not enough thiamin

Question 48

wet beri beri

Answer 48

cardiovascular, rapidly fatal (bc cardiac component) severe physical effort + high carb intake = edema

Question 49

acute beri beri

Answer 49

infants anorexia, vomiting lactic acidosis heart failure

Question 50

Wernicke-Korsakoff syndrome alcohol addiction promotes low __ and __ damage

Answer 50

Wernicke-Korsakoff syndrome alcohol addiction promotes low **thiamin intake** and **liver** damage

Question 51

Wernicke encephalopahty

Answer 51

ataxia, abnormal motor function, paralysis of eye movements, amnesia, apathy

Question 52

wernicke-korsakoff treatment?

Answer 52

thiamin supplementation usually helps, but some damage is irreversible