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Biochemistry > Heme Metabolism > Flashcards

Heme Metabolism Flashcards

1
Q

How many grams of iron are there in an adult male?

A

3-4 grams

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2
Q

What is the daily iron uptake & excretion?

A

1 mg for each

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3
Q

How is iron excreted?

A
  • urine or stool
  • desquamination of skin & intestinal tract
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4
Q

What are the compounds that contain iron?

A
  • hemoglobin/myoglobin
  • enzymes
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5
Q

What are the compounds that store iron?

A
  • ferritin
  • hemosiderin
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6
Q

What is the driving force for movement of Fe?

A

bone/erythroid marrow

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7
Q

What is ferritin?

A

protein that stores iron primarily in the liver & kidney

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8
Q

What is the role of ferritin?

A

brings Fe from blood to other tissues

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9
Q

Is Fe oxidized before or after binding to transferrin?

A

before

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10
Q

What are the steps of dietary iron uptake with DMT1?

A
  1. Ingest food with Fe3+ in it
  2. Fe3+ makes its way into the gut
  3. Fe3+ is reduced into Fe2+ by ferrireductase
  4. Fe2+ is brought into enterocytes (cells lining the intestine) by DMT1 (Divalent Metal Transporter 1)
  5. Inside the enterocyte, Fe2+ can be stored as ferritin. But bulk of Fe2+ is transported into the blood
  6. In the blood, Fe2+ is oxidized to Fe3+
  7. Fe3+ binds transferrin to be transported in the blood to other tissues
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11
Q

What are the steps of iron transport with transferrin?

A
  1. Fe3+ binds transferrin to be transported in the blood to other tissues
  2. Diferric transferrin binds the transferrin receptor
  3. The diferric transferrin, bound to the transferrin receptor, is brought into the cell via a vesicle -> endosome
  4. Protons are pumped into the endosome which decreases the pH
  5. The decreased pH within the endosome causes Fe3+ to detach from transferrin
  6. Fe3+ is released into the cytoplasm of the cell
  7. Apo-transferrin (transferrin without iron bound to it) has high affinity for the transferrin receptor, so apo-tf remains attached to the receptor in the endosome
  8. The vesicle is externalized and apo-tf is released back into the blood to help transport more Fe3+
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12
Q

What is happening to most of the Fe in our body?

A

conserved/recycled for synthesis of heme towards Hgb production

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13
Q

What is the structure of heme?

A
  • planar molecule with 1 Fe & tetrapyrrole ring
  • stable due to resonance
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14
Q

What is the cell location of heme synthesis?

A

mitochondria & cytosol

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15
Q

What is the organ location of heme synthesis?

A

liver & bone marrow

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16
Q

What is the rate limiting enzyme for heme synthesis?

A

aminolevulinate synthase (ALAS)

17
Q

What are the 4 major steps in heme synthesis?

A
  1. Formation of the pyrrole
  2. Assembly of the tetrapyrrole
  3. Modification of side chains
  4. Oxidation & insertion of Fe2+
18
Q

What is the rate limiting step in heme synthesis?

A

succinyl-CoA + glycine -> aminolevulinate synthase (ALAS) -> aminolevulinate (ALA)

19
Q

What are the 2 important enzymes in heme synthesis?

A

aminolevulinate synthase (ALAS) & ferrochelatase

20
Q

How much ALA is needed to make PBG?

A

2

21
Q

How much PBG is needed to make a linear tetrapyrole?

A

2 (8 ALA)

22
Q

What is the enzyme needed between linear tetrapyrrole & uroporphyinogen?

A

Uro 3 synthase

23
Q

What are the characteristics of ALAS-1 in heme synthesis?

A
  • house keeping enzyme
  • present in ALL cells
  • regulated by heme at: transcription, RNA stabilzation, translation, translocation, formation of mature ALAS-1
24
Q

What are the characteristics of ALAS-2 in heme synthesis?

A
  • erythroid-specific isozyme
  • present ONLY in erythroid cells
  • regulated by heme at: transcription, translation, mitochondrial import, its activity
25
Q

What is the porphyria leading to neuropsychiatric symptoms in heme synthesis?

A

issues with beginning of heme synthesis -> accumulation of ALA or PBG

26
Q

What is the porphyria leading to blisters in heme synthesis?

A

issues with end of heme synthesis -> accumulation of porphryinogens -> photosensitivity

27
Q

What is the location of heme catabolism?

A

macrophages of the spleen & liver

28
Q

What is the rate limitng enzyme of heme catabolism?

A

heme oxygenase

29
Q

What is the rate limiting step for heme catabolism in the spleen?

A

heme -> heme oxygenase -> biliverdin

30
Q

What enzyme catalyzes the conversion of biliverdin into bilirubin?

A

biliverdin reductase

31
Q

What deficiency in bilirubin conjugation can cause diseases?

A

UDP glucuronyl transferase

32
Q

What is the enzyme used to turn bilirubin monoglucuronide into bilirubin diglucuronide + nilirubin?

A

dismutase

33
Q

What is the normal amount of serum bilirubin?

A

< 4 mg/dl

34
Q

What are the disorders of heme catabolism?

A
  • jaundice
  • Gilbert’s syndrome
  • Crigler-Naijar syndrome
35
Q

What is Gilbert’s syndrome?

A
  • deficeincy in hepatic bilirubin -> UDP glucuronyl transferase
  • can cause mild jaundice
36
Q

What is type 1 Crigler-Naijar syndrome?

A
  • absence of hepatic bilirubin
  • serum bilirubin >20 mg/dl
37
Q

What is type 2 Crigler-Naijar syndrome?

A
  • decrease in hepatic bilirubin
  • serum bilirubin < 20 mg/dl
38
Q

What causes photosensitivity in heme synthesis?

A

accumulation of porphyrinogen

Biochemistry (20 decks)

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