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Biochem + Metabolism > B Vitamins B&B > Flashcards

B Vitamins B&B Flashcards

1
Q

which B vitamin CAN be stored in the body?

A

B12 - stored mostly in liver, some in muscle

others (B1,2,3,5,6,7,9) wash out of body quickly (water soluble)

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2
Q

how do B vitamin deficiencies generally present?

A

B vitamins used in many metabolic pathways, deficiencies have greatest effect on rapidly growing tissues

—> dermatitis, glossitis, diarrhea, cheilitis (skin breakdown at corners of lips)

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3
Q

vitamin B1, aka _____, is a cofactor for which 4 enzymes?

A

vitamin B1 = thiamine, converted to thiamine pyrophosphate (TPP)

  1. pyruvate dehydrogenase
  2. Alpha ketoglutarate Dehydrogenase (TCA)
  3. Alpha ketoacid Dehydrogenase (branched amino acid chains)
  4. Transketolase (HMP shunt)
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4
Q

vitamin B2, aka _____, is required for…

A

vitamin B2 = riboflavin

added to adenosine to create FAD+ (required by dehydrogenases) used in and ETC (as FMN - flavin mononucleotide)

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5
Q

what are the classic symptoms of vitamin B2 deficiency?

A

vitamin B2 = riboflavin (used to make FAD+)

—> dermatitis, glossitis
—> cheilitis (lip inflammation, cracks at corner of mouth) - classic sign
—> corneal vascularization (rare)

[deficiency = ariboflavinosis]

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6
Q

Vitamin B3, aka _____ is used for…

A

vitamin B3 = niacin

used to synthesize NADH and NADPH - used in ETC, dehydrogenases require NAD+

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7
Q

niacin, aka vitamin ____, can be synthesized from which amino acid?

A

niacin = vitamin B3, used to generate NADH/NADPH

can be synthesized from tryptophan, conversion requires vitamin B6 (vit. B6 deficiencies will present with symptoms of niacin deficiency!)

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8
Q

patients with what type of diet will classically be deficient in niacin (vit. B3)?

A

corn-based diets - corn does not contain niacin

niacin (B3) found in grains, milk, meats, liver

can also be synthesized from tryptophan (requires B6)

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9
Q

how does vitamin B3 deficiency present?

A

vitamin B3 = niacin, used to make NADH/NADPH

niacin/B3 deficiency = Pellagra
—> Dermatitis
—> Diarrhea
—> Dementia
—> Death

—> rash on sun-exposed areas

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10
Q

Pellagra

A

niacin/B3 deficiency = Pellagra
—> Dermatitis
—> Diarrhea
—> Dementia
—> Death

—> rash on sun-exposed areas

vitamin B3 = niacin, used to make NADH/NADPH

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11
Q

what are 3 classic clinical scenarios in which niacin (B3) deficiency develops?

A

vitamin B3 = niacin, used to make NADH/NADPH

  1. INH (isoniazid, TB drug) - decreases B6 activity
  2. Hartnup disease - AR absence of AA transporter in proximal tubule, loss of tryptophan in urine
  3. Carcinoid syndrome - GI tumor secretes serotonin via altered tryptophan metabolism, tryptophan unavailable

[recall B3 can be made from tryptophan, and this conversion requires B6]

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12
Q

Pt with PMH of INH (isoniazid) therapy for TB is presenting with dermatitis, diarrhea, dementia, and a rash on sun-exposed areas. What is likely going on?

A

Niacin/B3 deficiency (Pallagra)

INH decreases B6 activity, and recall B3 can be made from tryptophan with the assistance of B6

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13
Q

Pt with Carcinoid syndrome is presenting with dermatitis, diarrhea, dementia, and a rash on sun-exposed areas. What is likely going on?

A

niacin/B3 deficiency (Pellagra)

Carcinoid syndrome: GI tumor secreting serotonin - alters tryptophan metabolism such that most of it is used to synthesize serotonin (when usually only 1%) —> tryptophan deficiency

recall B3 can be made from tryptophan (requires B6 for conversion)

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14
Q

for what is niacin/vitamin B3 used as a treatment, and what occurs if it is taken in excess?

A

niacin/B3 - used to treat hyperlipidemia (separate from its role in generated NADH/NADPH)

in excess —> facial flushing via prostaglandin stimulation (can blunt with aspirin, which inhibits prostaglandins)

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15
Q

vitamin B5, aka ______, is used for…

A

vitamin B5 = pantothenic acid, used to coenzyme A (therefore any reaction requiring CoA also requires B5)

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16
Q

what is a classic sign of vitamin B5 deficiency?

A

vitamin B5 = pantothenic acid, used to coenzyme A

deficiency rare, but may present with “burning feet” (numbness)

17
Q

vitamin B6 is composed of 3 compounds, which are all converted to ______

A

pyridoxal phosphate, PLP (active form of Vitamin B6)

used in:
- aminotransferase reactions
- neurotransmitter synthesis
- methionine —> cysteine pathway
- histamine synthesis
- glycogen breakdown (glycogen phosphorylase)
- tryptophan —> niacin conversion
- heme synthesis (ALA synthesis)

18
Q

which 5 neurotransmitters require vitamin B6 for their synthesis?

A

active form of vitamin B6 = pyridoxal phosphate

  1. dopamine
  2. norepinephrine
  3. epinephrine
  4. serotonin
  5. GABA

basically all the main ones !

19
Q

glycogen phosphorylase requires which vitamin?

A

glycogen phosphorylase requires Vitamin B6 (pyridoxal phosphate)

20
Q

what type of anemia occurs from vitamin B6 deficiency and why?

A

vitamin B6 = pyridoxal phosphate, required for a butt ton of reactions include heme synthesis

required for synthesis of ALA (gamma-aminolevulinic acid)

B6 deficiency —> sideroblastic anemia (iron cannot be incorporated into heme, and so it accumulates in RBC cytoplasms) - microcytic, hypochromic

21
Q

patients taking isoniazid (INH) for TB take supplements of vitamin ____ because…

A

isoniazid (INH) has similar structure to B6 (pyridoxal phosphate) and can inactivate it —> relative B6 deficiency

therefore, patients on INH must take B6 supplements

22
Q

what are the classic symptoms of vitamin B6 deficiency?

A

vitamin B6 = pyridoxal phosphate, used in lots of reactions

deficiency is very rare, but can cause CNS symptoms - seizures, confusion, neuropathy

also possible glossitis, oral ulcers

23
Q

which B vitamin is the only one to pose a threat of potential toxicity, and how does this present?

A

B vitamins are water soluble, excess is usually washed out

exception is B6 (pyridoxal phosphate) - massive intake (via supplements) may cause sensory neuropathy —> pain/numbness in legs, difficulty walking

24
Q

vitamin B7, aka _____, is required for which 3 important metabolic enzymes?

A

vitamin B7 = biotin, cofactor for carboxylation enzymes* (add 1 carbon group via CO2)

  1. pyruvate carboxylase (gluconeogenesis)
  2. acetyl CoA carboxylase (fatty acid synthesis)
  3. propionyl-CoA carboxylase (entry into TCA cycle)

*”ABC” enzymes - require ATP, Biotin, and CO2

25
Q

vitamin B7/biotin deficiency is very rare, but is classically caused by…

A

massive consumption of raw egg whites - contain avidin, which binds B7 and prevents its absorption

26
Q

which B vitamin is NOT absorbed in the jejunum?

A

B12 - absorbed in terminal ileum

27
Q

which 2 B vitamin deficiencies cause megaloblastic anemia and what are the classic findings?

A

folate (B9) or B12 deficiencies - required for thymidine synthesis (for DNA synthesis)

—> high levels of homocysteine (cannot be converted to methionine)
—> hypersegmented neutrophils
—> large RBC (high MCV)

[recall B12 deficiency will also present with elevated methylmalonic acid, required for myelin synthesis]

28
Q

vitamin B12, aka _____, comes from…

A

vitamin B12 = cobalamin (contains cobalt)

only synthesized by bacteria, found in meats

dietary deficiency very rare, liver can store years worth of B12

29
Q

what is the unique role of vitamin B12 (cobalamin) from folate (B9) that helps distinguish a B12 deficiency from a folate deficiency?

A

both will present with elevated homocysteine (—> megaloblastic anemia)

but vitamin B12 is also required for odd chain fatty acid metabolism —> high levels of methylmalonic acid (MMA), defect in myelin synthesis —> peripheral neuropathy involving dorsal spinal columns (subacute combined degeneration (SCD)

bilateral, legs > arms, ataxia, loss of vibration and position sense

30
Q

what is the cause of pernicious anemia?

A

autoimmune destruction of gastric parietal cells —> loss of secretion of intrinsic factor —> defect in B12 absorption in the terminal ileum

type II hypersensitivity, associated with HLA-DR antigens

31
Q

what vitamin deficiency is associated with pernicious anemia?

A

autoimmune destruction of gastric parietal cells —> loss of secretion of intrinsic factor —> defect in B12 absorption in the terminal ileum

type II hypersensitivity, associated with HLA-DR antigens

32
Q

how does pernicious anemia present?

A

autoimmune destruction of gastric parietal cells —> loss of secretion of intrinsic factor —> defect in B12 absorption in the terminal ileum

presents with chronic inflammation of the gastric body, more common among women, associated with gastric adenocarcinoma

33
Q

what are the 4 forms of vitamin B1 deficiency?

A

B1 = thiamine, deficiency = Beriberi

dry: muscle wasting, peripheral neuropathy (feet)

wet: edema, enlarged heart

infantile: heart failure (babies breast-fed by thiamine deficient mothers)

cerebral (Wernicke-Korsakoff): ataxia, impaired mental status (alcoholism)

34
Q

vitamin B9, aka _____, is important for…(3)

A

B9 = folate (folic acid)

  1. DNA/RNA synthesis
  2. methionine recycling (conversion of homocysteine to methionine)
  3. SAM (S-adenosylmethionine) synthesis, for methylation reactions
35
Q

what occurs from vitamin B9 deficiency?

A

B9 = folate

—> DNA strand breaks (recall folate required for DNA/RNA synthesis)
—> hyperhomocysteinemia (recall folate is required to convert homocysteine to methionine)
—> megaloblastic anemia
—> neural tube defects (spinal bifida, anencephaly)

36
Q

what will a peripheral smear show in a patient with vitamin B9 deficiency?

A

B9 = folate, deficiency —> megaloblastic anemia

peripheral smear shows macrocytic anemia + hypersegmented PMNs

Biochem + Metabolism (18 decks)

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