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025. My MCM Test 2 > Heme Synthesis and Breakdown > Flashcards

Heme Synthesis and Breakdown Flashcards

1
Q

What is Hb made of and what is at the center of each subunit?

A

It is made up of 2 alpha globins and 2 beta globins, each subunit is made up of 4 pyrrole rings (tetra pyyrole), called porphyrin ring. Iron Fe2+ (ferrous) is bound in the middle of each porphyrin ring

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2
Q

Where do the different stages of the biosynthesis of heme occur?

A

Phase one: Mito
Phase two: cytosol
Phase three: Mito

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3
Q

What is the first step in phase one of heme biosynthesis?

A

Glycine + Succinyl CoA forms Aminolevulinic acid (ALA) using ALA synthase and B6 (PLP)

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4
Q

What is the difference between ALASynthase 1 and ALASyntahse II?

A

1 is ubiquitous and 2 is only in BM and has an iron response element in mRNA

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5
Q

What happens once ALA is transported into the cytosol?

A

ALA dehydratase is used to form porphobilinogen (one pyyrole ring)

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6
Q

How is porphobilinogen made into hydroxymethylbilane?

A

4 of the porphobilinogens are by porpholinogen deaminase to form hydroxymehtylbilane (4pyyrole rings= to porphyrin ring)

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7
Q

How is hydroxymethylbilane made into Copro-porphyrinogenIII (2 steps)?

A

Using urophyrinogen synthase III to form Uro-porphyrinogen III and then uroporphyrinogen decarboxylase to form Copro-porphyrinogenIII

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8
Q

Once copro-porphyrinogen III is transported back into the mitochondria, how does it become Heme?

A

By using copro-oxidase which forms proto-porphyrinogen IX, combined with proto-porphyrinogen IX oxidase to form proto-porphyrin IX WHICH USES FERROCHELATASE TO FORM HEME

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9
Q

What does lead (from lead poisoning) inactivate, what is there a buildup of, and what disease does it cause?

A

Inactivates: ALA dehydratase and ferrochelatase
BuildUp: ALA & protoporphyrin IX
Anemia/ decrease energy production

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10
Q

What is porphyrias and what are the types?

A

Inherited metabolic disorders in heme synthesis . Two types: acute hepatic (liver), erythropoietic (bone marrow)

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11
Q

What is the defective enzyme and type of porphyria associated with acute intermittent porphyria?

A

E: porphoblinogen deaminase (PBG)
T: Hepatic porphyria

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12
Q

What is the defective enzyme and type of porphyria associated with Congenital erythropoietic porphyria?

A

E: uroporphyrinogen III synthase
T: Erythropoietic (BM)

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13
Q

What is the defective enzyme and type of porphyria associated with Porphyria cutanea tarda (PCT)?

A

E: Urophyrinogen decarboxylase
T: Hepatoerythropoietic (both liver / BM)

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14
Q

What is the defective enzyme and type of porphyria associated with Variegate porphyria (celebrity deaths)?

A

E: protoporphyrinogen IX oxidase
T: hepatic

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15
Q

What does congential erythropoietic porphyria cause a build up of and what is the product/side affect?

A

Causes a build up of uroporphyrinogen I and its oxidation product uroporphyrin I which is fluoroescent

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16
Q

What is the first step of heme degredation? What is used and produced?

A

Heme produces Biliverdin by heme oxidase. This reaction uses O2 and produces CO and Fe3+ (ferric)

17
Q

How is biliverdin made into Bilirubin?

A

Using biliverdin reductase and NADPH (removes double bond)

18
Q

What happens to billirubin once it is released into the bloodstream as free/indirect/unconjugated BR (insoluble)?

A

Binds to albumin and transported to liver where BR is conjugated with glucuronic acid (Bilirubin Diglucuronide), now called conjugated/direct BR.

19
Q

How is UDP glucuronate made and what catalyzes the reaction between UDP glucuronate and bilirubin?

A

Made by UPD Glucose (2NAD) and UDP glucose dehydrogenase, 2 UDP glucuronate are combined with bilirubin by Bilirubin UDP glucuronyltransferase, forming Bilirubin Diglucuronide

20
Q

When newly synthesized bilirubin diglucuronide is released, where does it go and when is it released?

A

conjugated bilirubin is sent to the gull pladder which is eventually released into the small intestine in response to food

21
Q

What happens to conjugated bilirubin in the intestine?

A

The diglucuronides are removed and bilirubin is reduced to urobilinogen

22
Q

What happens when the kidneys absorb urobilinogen?

A

it is made into urobilin (yellow) and excreted in urine

23
Q

What happens when urobilinogen undergoes further reduction in the intestine?

A

it is made into stercobilin (red-brown) and found in poop :)

24
Q

What causes jaundice and what are the different causes?

A

Hyperbilirubinemia, elevated levels of BR in blood

  1. pre-hepatic
  2. intra-hepatic
  3. post-hepatic
25
Q

What causes pre-hepatic jaundice?

A

increased production of unconjugated BR which causes elevated blood levels of unconjugated/indirect/free BR

26
Q

What causes intra-hepatic jaundice and some examples?

A

Impaired hepatic uptake (transporter), conjugation (transferase), or secretion of conjugated BR
EX: Criggler-Najjar Syndrome (no enzyme transferase)
Gilbert Syndrome

27
Q

What are some findings indicative of intra-hepatic issues?

A

High serum ALT/AST, Conjugated BR in urine

28
Q

What causes post-hepatic jaundice?

A

Cannot excrete billirubin, caused by decreased bile flow due to bile/gull stones

29
Q

What are some findings indicative of post-hepatic issues?

A

elevated blood levels of conjugated BR, BR in urine (dark), pale stool, not yellow urine

30
Q

What are neonatals deficient of and why (causes neonatal jaundice known as physiological jaundice)?

A

Deficient in UDP-GT (adds glucuronal to bilirubin) enzyme at birth-> fetal hemoglobin changes to HbA, cannot keep up with amount of bilirubin (NORMAL)

31
Q

What is a treatment for neonatal jaundice (2)?

A

Blue fluorescent light (converts BR to more soluble isomers)

Tinmesoporphyrin (strong inihibtor of heme oxygenase) stops formation of BR

32
Q

What is Crigler-Najjar Syndrome and what are the different types?

A

Syndrome resulting from deficiency of UDP-GT
Type I: complete absence of gene : Severe Hyperbilirubinemia, ultimately need liver transplant
Type II: Benign form, enzyme has 10% activity

33
Q

What is Gilbert Syndrome?

A

Common/Benign, Results in 25% activity of UDP-GT enzyme

Serum BR increases when fasting, stressed, or with alcohol

34
Q

What is hepatitis and what can it cause (regaurding BR as well)?

A

It is inflammation of the liver, leading to dysfunction.
Caused by Hep A,B,C, alcoholism
Increases levels of unconjugated and conjugated BR in blood, causing (intra-hepatic jaundice) yellow discoloration and dark urine

35
Q

BRUISING breaks down from heme to iron

A

Hg–> Heme-Red
Biliverdin-Green
Bilirubin-Orange
Hemosiderin (iron)- reddish brown

025. My MCM Test 2 (15 decks)

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