BMS 200 > B-Vitamins > Flashcards

B-Vitamins Flashcards

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1
Q

What is Vitamin B1?

A

Thiamin

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2
Q

What are the dietary sources of vitamin B1?

A
  • plant food which comes as “free” unphosphorylated thiamin
  • animals: 95% phosphorylated as TDP and 5% as TMP or TTP
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3
Q

What is important for digestion of thiamin

A

that it gets dephosphorylated

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4
Q

you can only absorb ? thiamin

A

unphosphorylated

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5
Q

there are two methods of absorbing thiamin (getting it into the SI). what are the two?

A
  • diffusion
  • carrier mediated transport (ThTr1, ThTr2)
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6
Q

thiamin is mostly in what form in the RBC?

A

TDP

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7
Q

What phosphorylate free thiamin into TDP?

A

Thiamin Pyrophosphokinase

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8
Q

When we store thiamin what form is it stored in?

A

TDP

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9
Q

who usually stores the thiamin?

A

skeletal muscles

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10
Q

how are thiamin excreted?

A

via urine as free thiamin or as 2 rings if bridge is broken

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11
Q

what dephosphorylates thiamin back into free form?

A

phosphatases

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12
Q

what is the function of thiamin diphosphate (TDP)?

A

oxidative decarboxylation (removal of 1 carbon)

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13
Q

usually which carbon does TDP remove

A

C #2

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14
Q

Where does TDP perform oxidative decarboxylation on?

A
  • pyruvate
  • alpha-ketoglutarate
  • 3branched amino acids
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15
Q

what does pyruvate turn into after oxidative decarboxylation?

A

Acetyl CoA

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16
Q

TDP converts alpha-ketoglutarate into ?

A

succinyl-CoA

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17
Q

what is succinyl-CoA important for?

A
  • used in the TCA/Kreb’s/ citric acid cycle
  • production of heme - important for hemoglobin/RBC production
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18
Q

what is pyruvate dehydrogenase complex composed of?

A

3 enzymes:
- TDP-dependent pyruvate dehydrogenase
- lipoic acid-dependent dihydrolipoyl transacetylase
- FAD-dependent dihydrolipoyl dehydrogenase

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19
Q

What does the pyruvate dehydrogenase complex requires to run?

A
  • TDP
  • FAD
  • NAD+
  • CoA
  • ATP
  • Mg2+
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20
Q

List the steps of how TDP converts pyruvate into Acetyl-CoA

A
  • TDP is ionized
  • TDP attaches its carbanion C-2 to the C-2 of pyruvate
  • pyruvate dehydrogenase then removes pyruvate’s CO2 resulting in hydroxyethyl-TDP
  • hydroxyethyl is removed from TDP and transferred to oxidized lipoamide resulting in acetyl lipoamide
  • acetyl lipoamide will complex A producing acetyl-CoA
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21
Q

what is the function of pentose phosphate pathway?

A
  • generate NADPH
  • interconvert phosphorylated sugars
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22
Q

what does transketolase do?

A

transfers 2 carbons from one ketose to another, depends on vitamin B1

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23
Q

what are thiaminases?

A

breakdown thiamin bridge

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24
Q

where do we get thiaminases?

A

enzymes found in some raw freshwater fish, shellfish, ferns

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25
how are thiaminases inactivated?
heat
26
what does sulphur dioxide do?
breaks thiamin bridge
27
where do you get sulphur dioxide for?
it's a preservative that is often found in dried fruits/vegetables, as well as alcoholic drinks
28
what does polyphenols do?
cause formation of thiamin disulfide which makes B1 more absorbable and more effective in function
29
where do we get polyphenols from
tannic acid and caffeic acid
30
how long does it take for the pathologies of deficiency of vitamin B1?
Can occur within weeks to 1 month of inadequate dietary intake
31
What is dry beriberi?
Peripheral neuropathy; symmetrical sensory symptoms and motor weakness of distal extremities
32
Where does dry beriberi typically begin?
in the feet
33
what is wet beriberi?
Cardiomegaly, tachycardia, right sided heart failure and peripheral EDEMA
34
What is Wernicke-Korsakoff syndrome?
Neurodegeneration brought on by thiamin deficiencies
35
Wernicke-korsakoff syndrome is often seen with what?
prolonged alcoholism
36
What are the symptoms of Wernicke-Korsakoff Syndrome?
§ Ophthalmoplegia (weak/paralyzed ocular muscles) § Nystagmus (involuntary eye movement) § Ataxia (impair coordination) § Amnesia (memory/ learning impairment) or confusion - Psychosis
37
What are the medications affecting thiamine?
- 5-fluorouracil - diuretics
38
what does 5-fluorouracil do?
inhibits phosphorylation of thiamin
39
what does diuretics do to thiamin?
increase excretion of thiamin
40
How can we test for thiamin activity?
transketolase activity test
41
Unlike Vitamin B1 there is no 1 condition associated with vitamin B2 deficiency instead deficiency results in a ?
combination of symptoms
42
where do we get vitamin B2?
milk, cheese, yogurt, liver, meat products, enriched grains
43
vitamin B2 is degraded by what?
sunlight
44
riboflavin is often ?
bound to protein or phosphate and needs to be liberated for absorption
45
How are vitamin B2 absorbed?
○ Small intestine: free riboflavin via RFVT transporter § However, large doses can be absorbed via diffusion
46
what interferes with vitamin B2 absorption?
alcohol
47
Vitamin B2 are stored in what form?
mostly as FMN, some FAD
48
Free flavin (Vitamin B2) does what to the urine?
bright yellow colour to the urine
49
What are the functions of vitamin B2
- reduction reactions - oxidizing agent by accepting hydrogens - supports ETC and metabolism of nutrients - nucleic acid metabolism - antioxidant - vitamin metabolism - metabolism of vitamin B6 and folate - metabolism of neurotransmitters (dopamine) - hydrogen peroxide
50
How are vitamin B2 levels tested?
measuring activity of FAD-dependent enzyme erythrocyte glutathione reductase
51
what are some therapeutic uses of vitamin B2?
- migraines - cataracts
52
What is pellagra?
it is a vitamin B3 deficiency causing dermatitis, diarrhea, dementia, and ultimately death
53
What is Vitamin B3 also called?
Niacin
54
Main food sources of Vitamin B3?
Fish, meats, poultry, liver, fortified cereals.
55
Is Vitamin B3 stable to heat?
Yes, it is very stable and doesn’t break down with cooking.
56
What forms of Vitamin B3 are found in animal foods?
Nicotinamide, NAD (nicotinamide adenine dinucleotide), and NADP (nicotinamide adenine dinucleotide phosphate).
57
What form of Vitamin B3 is found in plant foods, and is it well absorbed?
Nicotinic acid; most of it is bound to carbs/proteins and is not readily available for absorption.
58
Which pathway makes niacin from tryptophan?
the kynurenine pathway
59
Where does the Kynurenine Pathway take place?
in the liver
60
How much tryptophan is needed to make 1 mg of niacin?
60 mg of tryptophan → 1 mg of niacin.
61
what do we use to hydrolyse phosphate from NADP -> NAD?
pyrophosphatase
62
where is vitamin B3 absorbed?
in the small intestine
63
what does the glycohydrolase do?
breaks NAD and NADP into ADP-ribose and nicotinamide, which is then methylated and oxidized into various metabolites in the liver and excreted in URINE
64
NADP is reduced to NADPH during which two pathways?
- pentose phosphate pathway - mitochondrial membrane malate aspartate shuttle
65
what are the functions of nicotinic acid?
- causes prostaglandin release - causes enhanced fibrinolysis - improves lipid profile - increased histamine release - potential for hyperglycemia
66
what is the function of nicotinamide?
appears to be protective of insulin-secreting pancreatic beta cells
67
what are the 4D of pellagra?
- dementia - dermatitis - diarrhea - death
68
how can you test for vitamin B3?
- urine test for metabolites - blood test for NAD
69
What is Vitamin B5 also called, and why is it nicknamed “pantos”?
Pantothenic acid; “pantos” means “everywhere” because it is found in almost all foods.
70
Food sources of Vitamin B5?
Virtually all foods.
71
What destroys Vitamin B5?
Heat, freezing, acidity, and alkalinity. (Stable in drying and neutral solutions.)
72
Can gut bacteria synthesize Vitamin B5, and do we use it?
Yes, bacteria can make it, but it’s unclear how much we actually absorb/utilize.
73
In what forms does pantothenic acid exist in the diet?
Free pantothenic acid, bound pantothenic acid, and as part of coenzyme A (CoA).
74
Describe the digestion of Coenzyme A to pantothenic acid.
CoA → (pyrophosphatase) → 4’-phosphopantetheine → (phosphatase) → pantetheine → (pantetheinase) → pantothenic acid.
75
Where is Vitamin B5 absorbed, and by what transporter?
In the jejunum, mostly by sodium-dependent multivitamin transporter (SMVT).
76
How is Vitamin B5 absorbed at very high doses?
By passive diffusion.
77
Where is pantothenic acid stored in the body?
Present in all cells (pantothenic acid and 4’-phosphopantothenic acid); most converted into CoA. Actual storage amount is unclear.
78
How is Vitamin B5 excreted?
Catabolized back to pantothenic acid (via phosphatase and pyrophosphatase) and excreted intact in urine.
79
what are the functions of vitamin B5
- Energy production - Nutrient metabolism - Fatty acid synthesis - Folate metabolism
80
What is the main biochemical role of Vitamin B5?
It acts as part of Coenzyme A (CoA), carrying acetyl and acyl groups.
81
Which important CoA derivatives involve Vitamin B5?
Acetyl-CoA, propionyl-CoA, malonyl-CoA, succinyl-CoA.
82
What reactions does CoA facilitate with acetyl groups?
Acetylation reactions.
83
What is the role of acetyl-CoA in metabolism?
Links glycolysis (pyruvate) to the citric acid cycle (oxaloacetate).
84
How does pantothenic acid help with oxidative metabolism?
Promotes oxidative decarboxylation of pyruvate and α-ketoglutarate.
85
What molecules are synthesized using CoA?
Cholesterol, ketone bodies, fatty acids, phospholipids, sphingolipids.
86
Which neurotransmitter synthesis requires CoA?
Acetylcholine
87
Name three pathways where acetylation reactions (via CoA) are important.
Glycolysis, gluconeogenesis, citric acid cycle
88
Beyond metabolism, what structural/epigenetic roles does acetylation have?
Microtubule polymerization (cytoskeleton), histone acetylation (gene expression), acetylation of structural proteins (membrane functions).
89
What is the classic but rare deficiency syndrome of Vitamin B5?
Burning Foot Syndrome
90
What are the main causes of Vitamin B5 deficiency?
Alcoholism (low intake, possible malabsorption), diabetes mellitus (increased excretion), inflammatory bowel disease (malabsorption).
91
How is Vitamin B5 status best tested?
Urine test
92
What are the 4 general mechanisms that lead to B-vitamin deficiencies?
Inadequate intake, poor absorption, excess use, excess depletion.
93
What role does Vitamin B5 (via CoA) play in cholesterol synthesis?
Acetyl-CoA → mevalonate → cholesterol, with NADPH + H⁺ used along the way.
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