Thiamin

Front 1

Thiamin contains what two molecules that help determine its name?

Back 1

Sulfur (thio)
Nitrogen (amine)
thio-amine = thiamin
It is labile to heat and oxygen

Front 2

TPP

Back 2

Thiamin pyrophosphate
- This is the active coenzyme form of thiamin
- Also known as Thiamin diphosphate

Front 3

Food sources of thiamin

Back 3

Pork - most concentrated
Meat, whole grains, nuts/legumes, enriched grain (cereal) products

Front 4

Thiamin Absorption

Back 4

Low intake: active transport
Large (pharm) dose: passive diffusion
- Must be phosphorylated prior to absorption

Front 5

Thiamin chemical structure:

Back 5

Pyrimidine ring attached to a thiazole ring by a methylene bridge.
The reactive carbon is on the thiazole ring.

Front 6

Thiamin transport

Back 6

- Mainly transported while attached to albumin
- 90% of thiamin in blood is in erythrocytes

Front 7

Thiamin Storage

Back 7

Total of 30mg
- 50% of that is in muscle, primarily in TPP form

Front 8

Thiamin excretion

Back 8

Urine

Front 9

Thiamin main functions:

Back 9

1. Oxidative decarboxylation (the enzymes for it are thiamin dependent)
2. Transketolase is also thiamin dep.

Front 10

What two enzymes are used in oxidative decarboxylation?

Back 10

1. Pyruvate dehydrogenase
2. alpha-ketoglutarate dehydrogenase

Front 11

What does transketolase do?

Back 11

Connects the pentose phosphate pathway to glycolysis.
Feeds excess sugar phosphate molecules into the main carb metabolic pathway.

Front 12

How is thiamin converted into TDP?

Back 12

Diphosphate adds to the reactive carbon on the thiazole ring, producing TDP.

Front 13

What enzyme and cofactor are req to produce TDP from thiamin?

Back 13

Thiamin pyrophosphokinase and ATP. Products are AMP and TDP.

Front 14

During decarboxylation in the TCA cycle, TDP reacts with alpha-ketoglutarate and CoA to produce what?

Back 14

Succinyl CoA

Front 15

In the pyruvate dehydrogenase system, oxidative decarboxylation uses TDP to convert pyruvate into what?

Back 15

Acetyl CoA

Front 16

The biochemical function of thiamin in the pyruvate
dehydrogenase system is to what:

Back 16

pyruvate is attached to the thiazole ring of TDP and
CO2 removed by pyruvate decarboxylase

Front 17

What is the pentose monophosphate shunt?

Back 17

This is when verious sugars of different lengths are interconverted.
Produces pentose sugars, and connects with glycolysis and feeds excess sugars into the main carb metabolic pathway.

Front 18

Therefore, thiamin is essential for:

Back 18

Pentose sugar synth
NADPH and fatty acid synth
Transketolase (the enzyme req in pentose phosphate pathway.

Front 19

Is thiamin important for BCAA synthesis?

Back 19

Yes, it is req for the decarboxylation step that takes place on the alpha-keto acid that arose from transamination.

Front 20

What are the 3 BCAAs that are TDP dependent in synthesis?

Back 20

Valine
Leucine
Isoleucine

Front 21

DUring a thiamin def, what happens to the BCAAs?

Back 21

Cannot decarboxylate the alpha-keto acids, and there is an accumulation of organic acid metabolites.

Front 22

BeriBeri:

Back 22

Results from thiamin def:
- Affects the nervous system
- Confusion
- Muscle Weakness
- Ataxia (lack of coordination)
- Peripheral Paralysis

Front 23

Cardiac Abnormalities and Muscle Wasting:

Back 23

Both signs of thiamin def:
- Cardiac (we beriberi) = leads to edema (pitting)
- Muscle wasting = called dry beriberi

Front 24

How does thiamin regulate the nervous system?

Back 24

Decarboxylates alpha keto acids, without thiamin, cell death occurs due to buildup of organic acids from keto acids.
Helps in neurotransmitter synthesis.

Front 25

What are thiaminases and where do they occur?

Back 25

They break the methylene bridge of thiamin.
They are in high amounts in fish and shellfish, but are heat labile so cook your seafood to reduce bad thiaminases.
Also occurs in tea in the form of tannic acid, but is heat stable, so inc consumption of tea will reduce your thiamin levels.

Front 26

Why are asians at risk of thiamin def?

Back 26

They eat the betal nut, a CNS stimulant consumed in asia, contains tannins.
They also eat polished rice, fermented fish, and drink tea!

Front 27

Does alcohol affect thiamin absorption?

Back 27

yes, you can get Wernicke-Korsakoff syndrome - alcohol has a direct toxic affect on utilization of thiamin.

Front 28

What is the functional indicator for thiamin def?

Back 28

Transketolase stimulation test

Front 29

How does the transketolase stimulation test work?

Back 29

1. Measure the transketolase activity, then add TPP
2. If transketolase activity increases, patient is def.

Front 30

Assessing severity of thiamin def with transketolase stimulation test:

Back 30

Mild def - 15-25% inc
Severe def - more than 25% inc
BeriBeri - 40% or more inc

Front 31

What is the RDA of thiamin for males?

Back 31

1.2 mg/d

Front 32

What is the RDA of thiamin for females?

Back 32

1.1 mg/d

Front 33

Pregnant req how much thiamin?

Back 33

1.4 mg/d

Front 34

Lactating req how much thiamin?

Back 34

1.5 mg/d