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USMLE Biochemistry > B vitamins > Flashcards

B vitamins Flashcards

1
Q

What vitamins are water soluble?

A

B vitamins and vit C

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2
Q

What are common symptoms of B Vitamin defocencies?

A

Greatest effect on rapidly growing tissues

  • Dermatitis
  • Glossitis
  • Diarrhea
  • Cheilitis
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3
Q

What is Cheilitis?

A

Breakdown of skin surrounding lip

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4
Q

What is the active form of Thiamine?

A

Thiamine pyrophosphate (TPP)

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5
Q

What is thiamine a co-factor for? (4)

A
  • Pyruvate dehydrogenase
  • a-ketoglutarate dehydrogenase (TCA)
  • a-ketoacid dehydrogenase (branched chain amino acid)
  • Transketolase (HMP shunt)
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6
Q

What does Thiamine require to become Thiamine pyrophosphate?

A

ATP converted to AMP (2 phosphate groups lost)

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7
Q

What 3 enzymes make up the pyruvate dehydrogenase complex?

A
  • Pyruvate dehydrogenase (E1)

-

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8
Q

What are the 5 co-factors for the pyruvate dehydrogenase complex?

A
  • Thiamine (B1)
  • NAD+ (B2)
  • FAD+ (B3)
  • Coenzyme A (B5)
  • Lipoic acid
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9
Q

What does alpha-KG dehydrogenase create?

A

Succinyl-CoA (+ CO2 and NADH)

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10
Q

Deficiency of what enzyme causes Maple syrup urine disease?

A

Alpha ketoacid dehydrogenase

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11
Q

Transketolase transfers a carbon unit to create what?

A

Fructose-6-phosphate

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12
Q

Abnormality of transketolase can result in what disease?

A

Wernicke-Korsakoff syndrome

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13
Q

Describe Dry Beriberi syndrome?

A

Neurological and muscular

  • Polyneuritis
  • Muscle weakness

No edema (dry)

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14
Q

Describe Wet Beriberi syndrome?

A

Cardio related

  • Tachycardia
  • High output HF
  • Edema
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15
Q

Describe Wernicke-Korsakoff syndrome?

A
  • Confusion, confabulation
  • Ataxia
  • Opthalmoplegia (blurry vision)
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16
Q

What patients typically get Beriberi syndrome?

A

Malnourished

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17
Q

Why do malnourished patients often require thiamine first before glucose?

A

If without thiamine

  • Glucose cannot be metabolised as thaimine is required for pyruvate dehydrogenase
  • Can then worsen Wernicke-Korsakoff
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18
Q

What does Riboflavin metabolise?

A

FAD

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19
Q

Riboflavin + Adenosine creates what?

A

FAD+

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20
Q

FAD+ accepts 2 electrons what does it become?

A

FADH2

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21
Q

What enzymes is FAD+ required by

A

Dehydrogenases

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22
Q

What metabolic process is FAD+ essential to?

A

ETC

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23
Q

What complex in the ETC riboflavin essential for synthesising?

A

Flavin mononucelotide (FMN)

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24
Q

What are the symptoms of riboflavin deficiency? (rare)

A
  • Dermatitis
  • Glossitis
  • cheilitis (inflammation of lips, cracks in corners of mouth)
  • Corneal vascularisation
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25
Niacin used to synthesise what?
NADH NADPH | - ETC
26
NAD+ is required by what enzymes?
Dehydrogenases
27
Niacin can be synthesised from what amino acid?
Tryptophan
28
Tryptophan to Niacin requires what vitamin as a cofactor?
B6
29
What is Niacin found in? | What patients may get a deficiency?
- Grains - Milk, meat, liver Corn based diets -> deficiency
30
What are the symptoms of Niacin deficiency (Pellagra)?
- Diarrhea - Dermatitis - Dementia - Death 4 Ds
31
What are the skin findings in those with Pellagra?
- Sun-exposed areas - Initially like bad sunburn - Blisters, scaling - Dorsal surfaces of hands - Face, neck, arms and feet
32
What diseases/treatments can lead to Niacin deficiency?
- INH therapy (TB) - Hartnup disease - Carcinoid syndrome
33
How may INH therapy (isoniazid) (TB) cause niacin
- Isoniazid -> decreased B6 activity | - B6 required to synthesise niacin from tryptophan
34
What is Hartnup disease?
Absence of AA transporter in PCT - Loss of tryptophan in urine - > Niacin deficiency
35
How is hartnup disease inherited?
AR
36
How may carcinoid syndrome cause niacin deficiency?
- Up to 70% of Tryptophan is converted to serotonin in carcinoid - Normally only ~ 1% - Tryptophan deficiency (pellagra) reported
37
What vitamin may be given to treat hyperlipidemia?
Niacin | - Effects lipolysis directly (unrelated NAD/NADP)
38
Excess niacin results in what symptom?
Facial flushing | - Stimulates release of prostaglandins in skin
39
How may facial flushing be treated as a result of niacin treatment?
- Aspirin (inhibits prostaglandin) prior to niacin | - Fades with time
40
What is pantothenic acid essential in the synthesis of?
Coenzyme A
41
What is coenzyme A (created by pantothenic acid) required by?
- Dehydrogenase enzymes | - Acetyl-CoA
42
Beta oxidation reaction (Fatty acids to fatty acyl CoA) in fatty acid metabolism requires what coenzyme and therefore what vitmain?
Coenzyme A | - Pantothenic acid
43
B5 deficiency has what symptoms (v. rare)?
- GI: N/V, cramps - Numbness, paresthesias (burning feet) - Necrosis of adrenal glands (animal studies)
44
What are the different types of vit B6 and what are they all converted to?
- Pyridoxine (plants) - Pyridoxal, pyridoxamine (animals) - All converted to pyridoxal phosphate
45
B6 can be used as a cofactor for what reactions?
- Aminotransferase reactions (amino acids) - Cysteine creation (Homocysteine -> Cystathionine thru Cystathionine Synthase) - Histamine synthesis - Glycogen breakdown - Niacin - Heme synthesis
46
B6 plays a role in the pathways for
Neurotransmitters
47
What is Histamine created from?
Histidine
48
Histidine is converted to Histamine by what enzyme? | What does it require as a cofactor?
Histidine Decarboxylase (removes CO2) Vitamin B6 as cofactor
49
What enzyme in glycogen breakdown does B6 act as a cofactor for?
Glycogen phosphorylase
50
B6 is required for the synthesis of what substance in heme synthesis?
y-aminolevulinic acid (ALA)
51
Deficiency of B6 can cause what anemia?
Sideroblastic | - Iron cannot be incorporated into heme -> accumulates in cytoplasm
52
How can Isoniazid cause B6 deficiency?
Similar to B6 structure so forms inactive pyridoxal phosphate
53
What drug outside of isoniazid may cause B6 deficiency?
Oral contraceptives
54
What are the symptoms of a pure B6 deficiency? (v. rare)
CNS symptoms - Seizures - Confusion - Neuropathy Glossitis, oral ulcers
55
What B-vitamin has a potential toxicity?
B6
56
What are the symptoms of B6 toxicity?
- Pain/numbness in legs | - Sometimes difficulty walking
57
Biotin acts as a cofactor for what enzymes?
Carboxylation enzymes | - All add 1 carbon group via CO2
58
What carboxylation enzymes does biotin act as a cofactoe for?
- Pyruvate carboxylase - Acetyl-CoA carboxylase - Propionyl-CoA carboxylase
59
All carboxylase enzymes require what?
ABC - ATP - Biotin - CO2
60
Acetyl-CoA Carboxylase converts Acetyl CoA into what?
Malonyl-CoA
61
What substances can be converted to Propionyl-CoA and subsequently into the TCA cycle?
Amino acids - Valine - Methionine - Isoleucine - Threonine Odd chain fatty acids VOMIT mnemonic
62
Propionyl-CoA Carboxylase converts Propionyl into what?
Methylmalonyl-CoA This is then converted to Succinyl-CoA
63
How may one get Biotin deficiency? (v. rare)
Mass consumption of raw egg whites (avidin)
64
What are the symptoms of Biotin deficiency?
- Dermatitis - Glossitis - Loss of appetite - Nausea
65
Where are B vitamins absorbed (except B12)?
Jejunum

USMLE Biochemistry (44 decks)

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