Heme Synthesis Flashcards

1
Q

Where does heme synthesis occur (tissue)?

A

bone marrow

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2
Q

Where are cytochromes synthesizes (tissue)?

A

liver

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3
Q

What is the regulated step of heme synthesis? Where is this located?

A

succinyl-CoA + Glycine»ALA
Enzyme: aminolevulinine acid synthase (ALA synthase)
Location: mitochondria
**ALA is exported out to the cytoplasm for next reaction

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4
Q

Between porphobilinogen and uroporphyrinogen, which is photoactive?

A

uroporphyrinogen (from UPG synthase III)

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5
Q

How is heme synthesis inhibited?

A

end-product inhibition

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6
Q

How is heme synthesis stimulated?

A

increased demand for heme (ie heme-containing enzymes such as cytochrome P450)

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7
Q

In what organelle does heme get its iron insertion?

A

mitochondria

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8
Q

What’s the downside to heme regulation, especially when there’s a disorder?

A

If the end product is not made, the pathway doesn’t stop

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9
Q
  • deficiency in porphobilinogen deaminase

- PBG accumulates and gives urine dark red color

A

acute intermittent porphyria (AIP)

- intermittent because it’s only bad when heme synthesis is occuring

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10
Q
  • deficiency in uroporhyrinogen decarboxylase
  • absorbs UV light (after the photoactive product has been made), urine turns pink fluorescence
  • buildup of porphyrins
  • causes photosensitivity of the skin and leads to blistering of sun-exposed areas
A

PCT - Porphyria cutanea tarda

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11
Q
  • inhibitor of PBG synthase (cytosol) and ferrochlatase (mitochondria)
  • accumulation of ALA and other heme precursors
  • symptoms are similar to porphyria
A

lead poisoning

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12
Q

What reducing equivalent is required for heme degradation?

A

NADPH

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13
Q

Where does heme degradation occur?

A

spleen

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14
Q

Majority of bilirubin exits which route?

A

intestines as feces

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15
Q

Which organ needs to remain bilirubin-free?

A

brain

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16
Q

What’s another way bilirubin can exit the body?

A

kidney as urine

17
Q

Which route is the shortest way out for bilirubin, intestines or kidneys?

A

intestines

(spleen»albumin»liver»gut»feces

18
Q

What role does the liver have in the excretion of bilirubin?

A

makes it water-soluble by conjugation (via UGT - UDP-glucuronyltransferase)

19
Q

What intermediate of the bilirubin excretion pathway gets reabsorbed back to the liver and into circulation again?

A

urobilinogen (spontaneous oxidation to make urobilin)

20
Q

What turns bilirubin to urobilinogen?

A

bacteria in the gut

21
Q
  • increased destruction of RBCs causes serum bilirubin concentration to exceed the liver’s capacity for glucuronation and excretion
  • elevated serum levels of indirect bilirubin
A

prehapatic (hemolytic) jaundice

pre means before liver thus indirect

22
Q
  • pale color of feces and urine

- bilirubin in serum and tissues is mostly unconjugated

A

Hepatocellular Jaundice (liver disease)

  • also watch for elevated serum level of AST and ALT
  • mostly caused by hepatitis or acetaminophen poisoning
23
Q
  • pale color of feces but intense urine color

- bilirubin in tissues and urine is mostly conjugated

A

Cholestatic Jaundice (obstruction)

  • caused by gallstones, neoplasia and cirrhosis
  • watch for presence of alkaline phosphatase in serum (indicate block in bile duct)