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Metabolism > Simmon's Heme > Flashcards

Simmon's Heme Flashcards

1
Q

Where is heme biosynthesis the highest? What is he major use of heme in those 2 tissues?

A

Bone Marrow-hemoglobin

Liver-cytochromes

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2
Q

What is the structure of heme?

A

4 pyrroles joined by a bridging pattern, with a ferrous ion

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3
Q

First step in heme biosynthesis?
Product
Enzyme

A

Succinyl CoA+Glycine–>ALA

Enzyme: ALA synthase

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4
Q

Porphyrinogen

A
  • no double blonds at bridging carbons

- colorless

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5
Q

porphyrins

A
  • double bonds at bridging carbons

- colored, highly fluorescnet, photodegradable

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6
Q

How are porphoyrinogens oxidized to porphyrins?

A

non enyzmatically by light

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7
Q

How biosynthesis regulated in the liver?

A

heme inhibits its own synthesis by decreases the activity of ALAS1. (ALAS2 not regulated by heme)

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8
Q

Name the two simple molecules that contribute all the atoms for the organic portion of heme.

A

glycine and succinyl CoA

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9
Q

Porphyria

A

disease caused by a PARTIAL deficiency of one of the enzymes involved with heme biosynthesis.

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10
Q

What causes the symptoms in porphyria?

A

the increase in metabolic intermediates. not a decrease in heme production

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11
Q

Which two intermediates of heme biosynthesis are increased in acute intermittent porphyria?

A
  1. deficiency in porphobilinogen deaminase

- ->increased levels of ALA and porphobilinogen (PBG) and lower concentration of heme

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12
Q

What are this and other acute prophyrias characterized by?

A

nerve damage

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13
Q

What does the lower level of heme do in porphyria?

A

Reduces feedback inhibition of ALA synthase

  • increases ALA synthase
  • this leads to more ALA nad PBG
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14
Q

What factors exacerbate porphyria?

A

many drugs such as barbiturates, alcohol, steroids, low glucose diet
–>can incduce the expression of ALA synthase

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15
Q

How can the feedback inhibition of heme be used to treat porphyria?

A
  • Glucose infusion
  • intravenous administration of heme
  • ->suppress ALA synthase
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16
Q

What causes the photosensitivity seen in many porphyrias?

A

Deficiency: protoporphyrinogen oxidase
Increased: protoporphyrinogen and coproporphyrinogen in liver

Protoporphyrinogen and coproporphyrinogen are deposited in skin and sun converts them to porphyrins

Porphyrins are then further degraded by light- generates tissue destroying singlet oxygen

Can also occur with an increase in( porphyrinogens and porphyrins)

17
Q

What does catabolism of heme produce?

A

bilirubin

18
Q

What are 120 day old RBC taken up by and and destroyed?

A

phagocytic cells of the reticuloendothelial system

19
Q

What parts of hemoglobin are degraded?

A

globin and heme

Iron is reutilized

20
Q

What does heme oxgenase convert heme to?

A

biliverdin

21
Q

What does biliverdin reductase convert biliverdin into?

A

bilirubin (unconjugated bilirubin)

22
Q

How is bilirubin carried in the plasma and taken into the liver?

A

as a complex with albumin

taken up by active transport

23
Q

How bilirubin conjugated and by what?

A

Enzyme: UDP glucuronyl transferase

Conjugates bilirubin with glucoronic acid (via propionic side chains)

24
Q

Where is conjugated bilirubin secreted?

A

actively into bile canaliculus

25
Q

What happens to the conjugated bilirubin in the intestine?

A

-deconjugated by bacterial flora to urobilinogen
-urobilinogen can be taken up to enterohepatic circulation
or it continues to colon

26
Q

What happens to urobilinogen in the colon?

A

-oxidized to stercobilins(stool brown color) and urobilin (urine yellow color -kidney)

27
Q

Hyperbilirubinemia

A

elevated bilirubin in serum (above 1mg/dL)

  • conjugated or unconjugated
  • elevated bilrubin can diffuse into tissue, making them appear yellow (jaundice)
28
Q

When is jaundice detectable?

A

when serum bilirubin reaches 2-2.5 mg/dL

29
Q

What are the clinical consequences of hyperbilirubinemia?

A
  1. conjugated is benign

2. unconjugated at 25mg/dL –>bilirubin encephalopathy (kernicterus

30
Q

Hemolysis

A

increased destruction of RBCs

-unconjugated bilirubin

31
Q

Biliary obstruction

A

conjugated bilirubin not delivered to intestine and spills into blood
-urine dark, feces white-absence of stercobilins

-conjugated

32
Q

Hepatitis or cirrhosis

A

liver damage-decreased conjugation and excretion of bilirubin

-mixed unconjugated and conjugated

33
Q

Neonatal “physiological jaundice”

A
  • fragile RBCs
  • immature hepatic system-decreased uptake, conjugation, and excretion of bilirubin
  • bilirubin is also reabsorbed from the intestine

-unconjugated bilirubin

34
Q

Treatment of Neonatal “physiological jaundice”?

A

blue light or blue green light (for worse cases)
convert the insoluble and blood brain barrier unconjugated bilirubin into isomers taht are more soluble and cant get into brain
-isomers are excreted in urine or bile

Metabolism (13 decks)

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