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MCM - Final > Heme Synthesis & Breakdown - Staudinger > Flashcards

Heme Synthesis & Breakdown - Staudinger Flashcards

1
Q

How many subunits make up Hemoglobin? How many molecules of iron are present? 5

A

Four globular sub-units all bound to a single iron

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2
Q

Within heme where does iron reside? 5

A

Found in the center of a porphyrin ring (4) five membered rings

Iron is in its ferrous state –> Fe2+

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3
Q

What molecules contain heme? 5

A
  1. Hemoglobin
  2. Myoglobin
  3. Cytochromes
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4
Q

How many heme groups are within one hemoglobin? 6

A

4

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5
Q

What is a pyrrole, how many per heme and how are they connected to one another? 8

A

Pyrrole –> A five-membered nitrogen containing ring

Heme contains four pyrrole and they are connected by a single carbon

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6
Q

Where does heme synthesis occur? 8

A

Liver and erythroid cell (bone marrow)

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7
Q

What are the three phases of heme biosynthesis? 8

A

Phase I mitochondrial

Phase II Cytostolic

Phase III Mitochondria

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8
Q

During phase I (mitochondrial) how is ALA produced? 8

A

ALA (δ-aminolevulinic acid) is produced from glycine + succinyl coenzyme A (succinyl CoA)

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9
Q

Briefly, what happens during phase II (cytostolic) of heme biosynthesis? 8

A

ALA + ALA = porphobilinogen

4 porphobilinogen = coproporphyringoen III

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10
Q

What are porphyrias? 16

A

Inherited metabolic disorders

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11
Q

What causes porphyrias? 8

A

Defects in one or more stages of heme synthesis

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12
Q

What inhibits ALA synthase and is an example of feedback inhibition? 9

A

Heme and hemin

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13
Q

What enzyme adds Fe2+ to heme? 12

A

Ferrochelatase

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14
Q

Differentiate symptoms of acute hepatic versus erythropoietic porphyrias 16

A

Acute hepatic neurological symptoms

Erythropoietic skin, photosensitivity

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15
Q

What kind of Porphyrias is caused by mutation of Porphobilinogen deaminase (PBG)? What is the main feature? 14

A

Acute intermittent porphyria

Feature –> excessive production of ALA and PBG

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16
Q

What kind of Porphyria is caused by mutations of Uroporphyrinogen III Cosynthase? What is the main feature? 14

A

Congenital erythropoietic porphyria

Feature –> accumulation uroporphyrinogen I

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17
Q

What kind of inheritance is associated with congenital erythropoietic porphyria? What are some symptoms? 18

A

Autosomal recessive (the only porphyria that is!)

symptoms –> Photosensitivity, red color in urine and teeth, anemia

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18
Q

What kind of porphyria is caused by mutations of uroporphyrinogen decarboxylase? What is the main feature? 17

A

Porphyria cutaneous tarda

Feature –> accumulation of uroprophyrinogen III (which eventually converts to uroporphyrinogen I

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19
Q

What kind of porphyria is caused by mutations of protoporphyrinogen oxidase? What is the main feature? 17

A

Variegate porphyria (autosomal dominate)

Feature –> photosensitive & neurologic systems

20
Q

What is the first rate-limiting and highly regulated step of heme synthesis?

A

ALA Synthase (δ-aminolevulinic acid synthase) – requires B6

21
Q

What activates and inhibits ALA Synthase? 15

A

(+) vitamin B6

(+) PXR

(-) Heme (feedback inhibition)

(-) hemin (feedback inhibition)

22
Q

What enzymes are involved in phase I of heme synthesis? 15

A

ALA synthase

ALA dehydratase

23
Q

What enzymes are involved in Phase II of heme synthesis? 15

A

Porphobilinogen deaminase

Uroporphyrinogen III Cosynthase

24
Q

What enzymes are involved in phase III of heme synthesis? 15

A

Protoporphyrinogen oxidase

Ferrochelotase

25
Q

What vitamin does ALA Synthase require? 13

A

pyridoxal phosphate vitamin B6, w/o this patient will have anemia

26
Q

What is a major inhibitor of ALA dehydratase? 9

A

Lead –> causes anemia

27
Q

What is a major inhibitor of ferrochelatase? 9

A

Lead –> causes anemia

28
Q

What is a major event of phase 1? 13

A

Decarboxylation of succinyl CoA

29
Q

Where does break down of red cells occur? 18

A

In the spleen

30
Q

What is the role of Heme oxigninase? 18

A

removes the bridge between pyrrole rings of heme

31
Q

PXR regulates the expression of which enzymes? What family are they in? 18

A

UDP-glucuronyl transferase

UDP Glucoronysl transferase family members

32
Q

What’s the difference between urobilinogen and urobilin? 30

A

Urobilinogen colorless, found in feces

Urobilin colored, found in urine

33
Q

Where is bilirubin found? 20

A

in the blood

34
Q

What is the end product of heme oxygenase? 25

A

Biliverdin

35
Q

What is able to unregulate heme oxygenase 100x? 25

A

Heme

Metal ions

Phenylhydrazine

36
Q

What does stercobilin do to waste? 30

A

Gives feces its brown color

37
Q

What causes jaundice? 32

A

Hyperbilirubinemia

38
Q

In Pre-hepatic jaundice was enzyme is deficient? 34

A

Glucose 6-phosphate dehydrogenase deficiency

39
Q

What clinical findings characterize pre-hepatic jaundice? 35

A

Elevated blood levels of unconjugated or indirect billirubin

40
Q

What helps keep bilirubin in solution? 28

A

Albumin

41
Q

What is the rate-limiting enzyme in the removal of bilirubin from the blood? 28

A

Bilirubin UDP Glucuronyl transferase

42
Q

What clinical findings characterize intra-hepanic jaundice? 37

A

Impaired hepatic: uptake, conjugation, or secretion of conjugated billirubin

43
Q

What syndromes are associated with intra-hepatic jaundice? 37

A

Criggler-Najjar syndrome

Gilbert syndrome

44
Q

What clinical findings characterize post-hepatic jaundice? 40

A

Eleveated blood levels of conjugated billirubin –> problems with billirubin excretion

AST and ALT levels are normal –> means there must be a blockage

45
Q

What is significant about Gilbert’s syndrome? 42

A

Of all the genetic errors of billirubin metabolism Gilbert’s syndrome is the only autosomal dominant syndrome

46
Q

What deficiency causes Crigler-Najaf syndrome Type 1? What does it result in?47

A

Deficiency of UDP-GT

Result severe hyperbilirubinemia

47
Q

What is the clinical finding of Hepatitis? 49

A

Increased levels of unconjugated and conjugated bilirubin in the blood

MCM - Final (6 decks)

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