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USMLE > Biochemistry- Vitamins > Flashcards

Biochemistry- Vitamins Flashcards

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USMLE® Step 1 flashcards
1
Q

List the fat soluble vitamins

A

ADEK

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2
Q

List the Water Soluble vitamins

A

B1, B2, B3, B5, B6, B7, B9, B12, C

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3
Q

What are two primary sources of vitamin A ?

A

Liver and leafy vegetables

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4
Q

What is the function of Vitamin A?

A

Antioxidant, essential for normal differentiation of epithelial cells into specialized tissue, retinal pigment

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5
Q

What does Vitamin A prevent?

A

Squamous metaplasia

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6
Q

What conditions is Vitamin A used to treat

A

oral for cystic acne
All-trans retinoic acid for AML subtype M3
Measles

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7
Q

What issues does deficiency in vitamin A cause?

A

Night blindness, scaly and dry skin, corneal degeneration, bitot spots on conjunctiva, immunosuppression

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8
Q

Acute toxicity of excess Vitamin A

A

Nausea, vomiting, vertigo and blurry vision

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9
Q

Chronic toxicity of excess vitamin A

A

Alopecia, scaly skin, hepatomegaly, arthralgia, pseudotumor cerebri

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10
Q

Why must a patient take two types of birth control and have a negative pregnancy test before taking vitamin A?

A

it’s a teratogen (cleft palate, cardiac abnormalities)

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11
Q

What is ergocalciferol

A

Vitamin D2, derived from plants

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12
Q

What is cholecalciferol

A

Vitamin D3, derived from milk and sun-exposed skin (stratum basale)

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13
Q

What is the active form of Vitamin D?

A

1,25 (OH) D3 aka calcitriol. Synthesized by 1 alpha hydroxylase in the liver

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14
Q

What does a deficiency in 1 alpha hydroxylase result in?

A

Rickets type 1 (AR)

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15
Q

What is the function of vitamin D?

A

Increase absorption of calcium and phosphate in the intestines, increase bone mineralization at low levels and increase bone resorption at high levels

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16
Q

What does a deficiency of Vit D lead to?

A

Rickets in children, osteomalacia in adults. Breastfed babies need supplemental Vitamin D

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17
Q

What does an excess of Vitamin D lead to?

A

Hypercalcemia, hypercalciura, loss of appetite, stupor

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18
Q

How does granulomatous disease lead to excess vitamin D?

A

Increased activation by macrophages

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19
Q

What is the function of Vitamin E (tocopherol, tocotrienol)?

A

Antioxidant that protects RBCs and membranes from oxidative damage

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20
Q

What are consequences of Vitamin E deficiency?

A

Hemolytic anemia, acanthocytes on histology, posterior column and spinocerebellar tract demyelination

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21
Q

How is Vitamin E deficiency different from Vitamin B12 deficiency?

A

no megaloblastic anemia, no hypersegmented neutrophils, no elevation in serum methylmalonic acid

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22
Q

Which vitamin enhances the anticoagulation effect of warfarinV

A

Vitamin E

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23
Q

What is the function of Vitamin K

A

“K”oagulation; cofactor for gamma carboxylation of Glutamate residue of clotting proteins 2, 7, 9, 10 C and S.

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24
Q

What two scenarios have Vitamin K deficiency?

A

Neonates (sterile intestines)

Prolonged use of broad-spectrum antibiotics (killing intestinal flora)

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25
Q

What is the name if Vitamin B1

A

Thiamine

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26
Q

What is the function of Thiamine

A

TPP cofactor for most dehydrogenase enzymes in ATP-generating (glucose utilization) reactions

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27
Q

for which enzymes is Thiamine a cofactor

A

alpha-ketoglutarate dehydrogenase
Transketolase
Pyruvate dehydrogenase
Branched-chain ketoacid dehydrogenase

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28
Q

How is B1 deficiency diagnosed?

A

Increased RBC transketolase activity after B1 infusion

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29
Q

What vitamin is Wernicke-Korsakoff a deficiency in?

A

Thiamine B1

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30
Q

What is the classic triad presentation of Wernicke-Korsakoff

A

Confusion, ophthalmoplegia, ataxia (+ personality change, permanent memory loss, confabulation)

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31
Q

What is damaged in Wernicke-Korsakoff?

A

Medial dorsal nucleus of thalamus, mammilary bodies

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32
Q

What is wet beriberi?

A

Dilated cardiomyopathy and edema due to B1 deficiency

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33
Q

What is dry beriberi?

A

Polyneuritis and symmetrical muscle wasting due to B1 deficiency

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34
Q

Sources of thiamine?

A

Beef, legumes, liver, milk

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35
Q

Which vitamin is Riboflavin?

A

B2

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36
Q

What is the function of B2?

A

Cofactor FAD, FMN in succinate dehydrogenase reaction of TCA cycle (2ATP generation)

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37
Q

What are the consequences of B2 deficiency?

A

Cheilosis (lip thickening and fissures around corners) and corneal vascularization

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38
Q

Which vitamin is Niacin

A

B3

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39
Q

Where is Niacin derived from?

A

Tryptophan

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40
Q

Which cofactors is Niacin part of

A

NAD, NADP

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41
Q

Which two vitamins are required for the synthesis of B3?

A

B2 and B6

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42
Q

What clinical issue is B3 used to correct?

A

Dyslipidemia (lowers VLDL, increases HDL)

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43
Q

What are the 3Ds of B3 deficiency (pellagra)

A

Dementia
Diarrhea
Dermatitis (rash around collar bone, Casal’s necklace and sun exposed areas)

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44
Q

How can malignant carcinoid syndrome cause pellagra-like symptoms?

A

Increased metabolism of tryptophan so less B3 synthesis

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45
Q

What is Hartnup disease?

A

AR loss of neutral amino acid (tryptophan) transporters on enterocytes and rental tubule cells. Leads to amino aciduria, low tryptophan and thus B3 deficiency.

46
Q

Treatment for Hartnup disease?

A

High protein diet and nicotinic acid supplement

47
Q

How does isoniazid lead to B3 deficiency?

A

Decreases B6, which is needed to synthesize B3

48
Q

What is the name for Vitamin B5?

A

Pantothenic acid

49
Q

What is the function of B5

A

essential component for coenzyme A (Acyl CoA) and fatty acid synthase?

50
Q

Symptoms of Vitamin B5 deficiency

A

enteritis, alopecia, dermatitis, adrenal insufficiency

51
Q

Which vitamin is pyridoxine?

A

B6

52
Q

For which enzymes and reactions is B6 (PLP) a cofactor?

A

transaminations, carboxylations, and glycogen phosphorylase

53
Q

Which neurotransmitters is B6 needed to synthesize?

A

Serotonin, epinephrine, norepinephrine, dopamine, GABA

54
Q

What are the symptoms of B6 deficiency?

A

Convulsions, hyperirritability, peripheral neuropathy, sideroblastic anemia

55
Q

Why does B6 deficiency lead to sideroblastic anemia?

A

Impaired heme synthesis and iron excess

56
Q

Which drugs can induce B6 deficiency?

A

Isoniazid (suspect in TB patients) and oral contraceptives

57
Q

Which vitamin is biotin?

A

B7

58
Q

Which enzymes is biotin a cofactor for?

A

Carboxylation enzymes (add 1C)
Pyruvate carboxylase (3–>4)
Acetyl-coA carboxylase
Propionyl coA carboxylase

59
Q

What can cause B7 deficiency?

A

Rare but either antibiotic use or excessive ingestion of raw egg whites (body builders)

60
Q

Which vitamin is B9

A

Folate

61
Q

What is the function of folate

A

THF–> 1c methylation in synthesis of DNA/RNA bases

62
Q

What are the symptoms of folate deficiency

A

Macrocytic, megaloblastic anemia with hypersegmented polymorphonuclear cells; glossitis, no neuro symptoms

63
Q

How do you distinguish between a folate deficiency vs B12 deficiency?

A

Folate deficiency has increased serum homocysteine and normal methylmalonic acid levels. B12 deficiency has elevated homocysteine and methylmalonic acid levels

64
Q

Which two conditions commonly present with folate deficiency

A

alchoholism and pregnancy

65
Q

Where is folate absorbed in GI tract

A

jejunum

66
Q

Which drugs can cause folate deficiency

A

PMS: phenytoin, methotrexate, sulfonamides

67
Q

Neural tube defects are often due to deficiency in which vitamin/

A

Folate

68
Q

What is the major source of folate

A

leafy green vegetables

69
Q

Which vitamin is Cobalamin

A

B12

70
Q

How long does it take for body to deplete B12

A

Years

71
Q

What is the major source of B12

A

animal products

72
Q

What is the function of cobalamin (B12)

A

Cofactor for methionine synthase and methylmalonyl-coA mutase

73
Q

Which antibodies are diagnostic of pernicious anemia?

A

anti-intrinsic factor (low B12)

74
Q

What are the symptoms of folate deficiency?

A

Megaloblastic, macrocytic anemia; hypersegmented PMNs, parasthesias, subacute combined degeneration of dorsal columns and lateral corticospinal tracts and spinocerebellar tracts

75
Q

What is the consequence of prolonged B12 deficiency?

A

Irreversible nerve damage

76
Q

Which vitamin is ascorbic acid

A

Vitamin C

77
Q

What are the 3 major functions of Vitamin C?

A
  1. Facilitate iron absorption by reducing it to Fe2+
  2. Hydroxylation of proline and lysine in collagen synthesis (RER)
  3. Dopamine beta-hydroxylase (DA –> NE)
78
Q

What does vitamin C deficiency cause?

A

Scurvy: swollen, bleeding gums; bruising, petechiae, anemia, poor wound healing, corswcrew hair, weak immune system

79
Q

What does Vitamin C excess cause?

A

N/V/D, fatigue, calcium oxalate nephrolithiasis; increased risk of iron toxicity in people with transfusions or hemochromatosis

80
Q

What is a major manifestation of zinc deficiency?

A

acrodermatitis enteropathica (scaling, scathing rash around buttocks and genitalia)

81
Q

What are symptoms of zinc deficiency

A

delayed wound healing, hypogonadism, decreased axillary, facial, pubic hair, anosmia

82
Q

Which condition does protein malnutrition cause?

A

Kwarshiorkor

83
Q

Clinical manifestation of Kwarshiorkor

A

Edema, anemia, fatty liver (small child with swollen abdomen)

84
Q

What condition does total calorie malnutrition cause?

A

Marasmus– muscle wasting, loss of subcutaneous fat.. emaciation

85
Q

What are the three ways that alcohol is metabolized in liver?

A

1) Cytosol with Alcohol dehydrogenase (most common and robust)
2) Smooth ER with CYP2E1
3) Peroxisome with Catalase

86
Q

What is alcohol converted to in the cytosol of hepatocytes by alcohol dehydrogenase?

A

Acetaldehyde

87
Q

What do you gives someone with antifreeze (ethylene glycol) or methanol poisoning?

A

Fomepizole

88
Q

How does fomepizole function?

A

Inhibits alcohol dehydrogenase

89
Q

Which substances causes hangover symptoms?

A

Acetaldehyde accumulation

90
Q

What is the limiting reagent in ethanol metabolism?

A

NAD+

91
Q

How does Disulfiram interact with alcohol?

A

Inhibits acetaldehyde dehydrogenase, leads to hangover symptoms (nausea, vomiting, GI upset)

92
Q

How does ethanol metabolism affect NADH/NAD ratio?

A

Increases it

93
Q

What are the consequences in elevated NADH/NAD+

A

Lactic acidosis, fasting hypoglycemia, hepatosteatosis

94
Q

How does ethanol lead to fasting hypoglycemia

A

elevated NADH/NAD+ favors OAA–> malate (prevents gluconeogenesis)

95
Q

How does ethanol lead to hepatosteatosis (fatty liver)?

A

elevated NADH/NAD favors DHAP–>G3P

96
Q

Which 5 metabolic reactions take place in the mitochondria

A

beta-oxidation (fatty acid oxidation), acetyl-coA production, TCA cycle, oxidative phosphorylation, ketogenesis

97
Q

Which 6 metabolic processes take place in the cytoplasm?

A

Glycolysis, HMP shunt, synthesis of steroids (SER), proteins, fatty acids, cholesterol and nucleotides

98
Q

Which metabolic processes take place in both cytosol and mitochondria?

A

Heme synthesis, urea cycle, gluconeogenesis

99
Q

What is the end product of galactose metabolism?

A

Glucose-1-phosphate

100
Q

Elevated prolactin and hyperphenylalanemia suggest PKU due to which cofactor deficiency?

A

tetrahydrobiopterin (BH4)

101
Q

Why does decreased BH4 lead to increased prolactin?

A

You have less dopamine being produced to inhibit prolactin

102
Q

Which enzyme deficiency leads to porphyria cutanea tarda?

A

uroporhyrinogen decarboxylase (UROD)

103
Q

What are the sympotoms of porphyria cutanea tarda?

A

recurrent blistering on back of hands and forearms, small itchy spots, hyperpigmentation after rupturing

104
Q

Acute intermittent porphyria occurs with defect in which enzyme?

A

PBG deaminase

105
Q

What is the typical presentation of acute intermittent porphyria?

A

woman with neuropsychiatric issues and abdominal pain

106
Q

Which vitamin is required for activity of ALA synthase? (Heme synthesis)

A

B6

107
Q

Wild mushrooms contain a toxin that inhibits synthesis of which molecule?

A

messenger RNA (inhibit DNA Pol II)

108
Q

Deficiencies of which vitamins is associated with hyperhomocysteinemia?

A

B6, B12, B9 (folate)

109
Q

What is hyperhomocysteinemia associated with?

A

atherosclerosis and thrombotic events

110
Q

Which urea cycle disorders are accompanied by hyperammonemia and excessive amounts of orotic acid?

A

Citrullinemia and ornithine transcarbamylase deficiency

111
Q

Which vitamin deficiency can cause infertility and decrease serum phospholipids?

A

Vitamin E

USMLE (36 decks)

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