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MCM-COM 2018 > Heme Synthesis And Breakdown > Flashcards

Heme Synthesis And Breakdown Flashcards

1
Q

Describe the structure of hemoglobin

A

*made of 4 heme

1 heme= 1 porphyrin ring—>4 pyrolle—> 1 ferrous iron

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2
Q

What state is iron in in Hb?

A

Ferrous
2+ state

*oxidation to Fe3+ (ferric) inactivates hb

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3
Q

What structures are heme present in?

A

Hemoglobin
Myoglobin
Cytochromes

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4
Q

They are three phases of heme synthesis, where do they take place?

A

P I and III - mitochondria

P II - cytosol

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5
Q

What parts of the body does most heme synthesis occur

A

Liver and bone marrow

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6
Q

Defect in one or more stages of heme synthesis can cause

A

Porphyrias (lots of porphyrin)

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7
Q

Basic outline of Phase 1 of heme synthesis

A

Reactants:

  1. Glycine
  2. Succinyl co A

Products:
ALA

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8
Q

Basic outline of heme synthesis phase 2

A

2 ALA —> porphobilinogen

4 porphobilinogen—>tetrapyrole ring of coproporphyrinogen III

*MAKES PORPHYRIN RING

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9
Q

Basic outline of heme synthesis stage 4

A

Coproporphyrinogen III—> protoporphyrinogen IX —> protoporphryin IX —> add Fe2+ —> heme

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10
Q

What coenzyme is needed in Phase 1 of heme synthesis for ALA synthase

A

Vitamin B6 (PLP)

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11
Q

Why does B6 deficiency cause anemia

A

Because ALA synthase needs it to make heme

*no heme = anemia

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12
Q

What are the 2 isoforms of ALA

A

ALAS 1 (everywhere)

ALAS 2 (in bone marrow only) 
-has an iron response element in mRNA
  • INHIBITED BY HEME and HEMIN
  • ACTIVATED BY IRON
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13
Q

What activates and inhibits ALA synthase

A

Inhibited by HEME / HEMIN

Activated transcription by IRON

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14
Q

What two enzymes does lead inactivate

A 
ALA dehydratase ( makes PBG)
*has zinc

Ferrochelatase (adds iron)
*has Fe

[accumulation of ALA and protoporphyin IX ]

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15
Q

What three impacts on the body’s healthy does lead poisoning have ?

A
  1. Neurological affects
    (ALA resembles GABA)
  2. Anemia
    (Bc no heme)
  3. Impacts energy production
    (Affects cytochromes heme)
    *fatigue
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16
Q

What is the Greek definition of porphyrias

A

Purple pigment

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17
Q

What is the general defect in porphyria

A

*inherited metabolic disorder

DEFECT IN HEME SYNTHESIS

  • acute hepatic = Neuro problems
  • erythropoietic = photosensitivity
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18
Q

Acute intermittent porphyria is related to what enzyme defect? Where?

A

Porphobilinogen deaminase
(PBG—> hydroxymethybilane)

**HEPATIC

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19
Q

Congenital erythropoietic porphyria is related to what enzyme defect? Where?

A

Uroporphyrinogen III cosynthase
(Hydroxymethylbilane —> uroporphyrinogen III)

  • erythropoietic
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20
Q

porphyria cutaneous Tarda is related to what enzyme defect? Where?

*MOST COMMON IN US

A

Uroporphyrinogen decarboxylase
(Uroporphyrinogen III —> coproporphyrinogen III)

*LIVER AND erythropoietic

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21
Q

Variegate porphyria is related to what enzyme defect? Where?

*celebrites

A

Protoporphryinogen oxidase
(Protophyrinogen IX —> protoporphrin IX)

*HEPATIC

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22
Q

In congenital erythropoietic porphryia, there is a build up of _______ , which oxidizes into _____. This causes what symptoms ?

A

Uroporphyrinogen I

Uroporphyrin I (not a heme intermediate)

  • red urine
  • red teeth
  • skin photosensitivity
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23
Q

What system handles hemoglobin degradation

A

Reticulo-endothelial system

  • globin breaks —> amino acids
  • heme removed for degradation
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24
Q

Heme is broken into biliverdin by what enzyme

A

Heme oxygenase
[needs oxygen]

*porphryrin ring —> tetrapyrrole rings

25
What is released during heme degradation by heme oxygenase
Carbon monoxide
26
During heme degradation, what happens to iron
Iron IX oxidized Ferrous—>ferric 2+—> 3+
27
What enzyme converts biliverdin to bilirubin?
Biliverdin reductase -removes double bonds *uses NADPH
28
What binds to free unconjugated (insoluble) bilirubin when it is first released into the bloodstream?
Albumin
29
The bilirubin-albumin complex is made and transported where so that bilirubin can be conjugated
The liver
30
In the liver (hepatocytes), bilirubin is conjugated with ________ to make it double
Glucuuronic acid
31
UnConjugated/free/indirect bilirubin vs conjugated/direct bilirubin
Newly released bilirubin is insoluble and is unconjugated Bilirubin + glucuronic acid = is soluble and is conjugated
32
What is the general outline of bilirubin conjugation in the liver
1. Glucose is made into UDP-glucouronate | 2. UDP-glucuronate + BR conjugated (by BR-UDP glucuronyl transferase) to make BR-monogluconide
33
What is the RLS of bilirubin blood removal
BR-monoglucuronide to diuronide
34
Defect in what enezyme of bilirubin conjugation gives rise to many jaundiced
Bilirubin-UDP glucuronyltransferase
35
What are the colors associated with heme, biliverdin, and bilirubin
Purple Green Red-orange
36
Conjugated bilirubin is then sent where to be stored until use ?
Stored in the gallbladder as bile
37
Explain what happens to conjugated bilirubin (BR-diglucuronide) after it leaves the gallbladder
1. Converted to free bilirubin 2. —> urobilinogen 3. Sent to kidneys (reabsorbed) or sent to colon (not reabsorbed)
38
What happened when urobilinogen is sent to the colon? Kidneys? And what is the associated colors?
Colon: —> stercobilin —>feces Kidney: —>urobilin —> urine * urobilnogen is colorless * stercobilin is brown * urobilin is yellow
39
Jaundice is also known as
Hyperbilirubinemia *elevated blood bilirubin Imbalance of production and excretion
40
What are the 3 types of Juandice
1. Pre-hepatic 2. Intracellular-hepatic 3. Post-hepatic
41
Causes of pre-hepatic juandice
*increased unconjugated bilirubin production (Also: hemolytic anemia’s, hemorrhage, liver cant conjugate bilirubin, G6P dehydrogenase deficiency, imcompability of maternal-fetal blood )
42
What are pre-hepatic jaundice findings
*elevated unconjugated bilirubin - normal conjugated BR blood levels - normal ALT/AST - normal urine
43
Causes if intra-hepatic jaundice
* impaired hepatic uptake (faulty transporter) * impaired conjugation * impaird secretion of conjugated BR Or hepatic dysfunction from CRIGGLER-NAJJAR SYNDROME or GILBERT SYNDROME
44
Intra-hepatic jaundice findings
* increased ALT/AST * conjugated-BR in urine - variable direct/indirect BR in blood - urobilinogen urine normal
45
What causes post hepatic jaundice (cholestatic jaundice or cholestasis)
*problem with indirect bilirubin excretion From obstruction: gall stones, tumors, drugs,....
46
Post-hepatic jaundice findings
* elevated conjugated BR *conjugated BR in urine *no urine urobilinogen DARK URINE, PALE STOOL -normal AST/ALT
47
What is the cause of neonatal (physiological) jaundice
- elevated unconjugated BR - immature hepatic metabolic pathway cant conjugate - UDP-GT enzyme deficiency
48
What is phototherapy?
* treatment for neonatal juandice | - blue fluorescent light makes Bilirubin more soluble
49
Besides phototherapy, what is another way to treat physiological juandice? (Not pathological)
-intramuscular injection of tinmesoporphyrin which inhibits heme oxygenase therefore stopping bilirubin production TINMESOPORPHYRIN INJECTION
50
What are the three UDP-GT related disorders? (Converts indirect bilirubin —>direct)
Crigler-Najjar syndrome I Crigler-Najjar syndrome II Gilbert syndrome
51
- complete absence of UDP-GT gene - no bilirubin conjugation - SEVERE HYPERBILIRUBINEMIA (jaundice)
Criggler-Najjar Syndrome Type 1
52
What happens if babies develop Criggler-Najjar syndrome type 1
- indirect bilirubin accumulates in brain | - causes KERNICTURUS encephalopathy and brain damage
53
What are the treatment options for Crigler-Najjar syndrome type 1
``` Blood transfusion Phototherapy Heme oxygenase inhibitors Oral calcium phosphate/carbonate LIVER TRANSPLANT ```
54
What does oral calcium phosphate/carbonate do in relation to bilirubin
Forms a complex with bilirubin in the the gut
55
- mutation in UDP-GT gene | - decreased activity of conjugated BR formation
Criggler-Najjar syndrome type 2
56
- reduced UDP-GT activity - common, benign disorder - elevated issues with fasting, stress, or alcohol
Gilbert syndrome
57
In hepatitis (liver inflammation) the liver dysfunction (from many different causes) has what affect on bilirubin? Therefore what effect on the body?
-increased levels of indirect/direct bilirubin in blood - skin and sclera become yellow - urine becomes dark
58
Color changes in brushing:
Heme(red/purple)—>biliverdin(green) —> bilirubin (orange)—> hemosiderin (brown)

MCM-COM 2018 (14 decks)

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