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MCP > L4_Heme Metabolism > Flashcards

L4_Heme Metabolism Flashcards

1
Q

How many pyroles in a porphyrin ring?

A

4

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2
Q

How many members in a pyrole ring?

A

5

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3
Q

name the order of the substituent groups on heme?

A

MVMVMPPM
m=methyl
p=propionate
V=vinyl

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4
Q

what isomer of protoporphyrin is in heme?

A

protoporphyirn IX

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5
Q

What is heme called if it has Fe3+

A

hemin

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6
Q

Describe the differences between Heme A, B, and C

A

Heme A contains a modification to the number 2 vinyl group
Heme B is the standard
Heme C is covalently bound to cysteine residues of proteins through the two vinyl groups

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7
Q

What is different about the axial ligands of Heme C when compared to A and B

A

It uses a methionine group as one of its axial ligands

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8
Q

What are the two basic, simple precursors of Heme?

A

Glycine and Succinyl Coenzyme A

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9
Q

How many ALA molecules to make a pyrole?

A

2

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10
Q

How many glycine and Succinyl CoA to make an ALA?

A

1

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11
Q

How many ALA per heme?

A

8

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12
Q

How many glycine and Succinyl CoA per Heme?

A

8 each

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13
Q

What does ALA stand for?

A

Aminolevulinate

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14
Q

Where are most metabolic pathways normally regulated?

A

At the first step

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15
Q

how many ALAs per porphobilinogen?

A

2

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16
Q

What is the enzyme that converts 2 ALA to porphobilinogen?

A

ALA dehydrase

17
Q

Where does ALA dehydrase work?

A

cytosol

18
Q

What can inhibit ALA dehydrase?

A

lead, binds where a normal Zn cofactor normally binds

19
Q

What 2 enzymes does lead inhibit, what builds up in each of these situations?

A

it inhibits ALA dehydrase and results in a build up of ALA which resembles GABA and fucks up brain development. It also inhibits ferrochelatase which causes coproporphyrinogen III to build up in the serum.

20
Q

How many porphobiligens per uroporphyrinogen?

A

4

21
Q

Describe how porphobiligen gets to uroporphyrinogen III, where does this take place?

A

4 porphobiligens are condensed and cyclized into the tetrapyrole ring uroporphyrinogen I by urophorphyrinogen synthase. Uroporphyrinogen I is them isomerized to uroporphyrinogen III by uroporphyrinogen III cosynthase. This all happens in the cytosol.

22
Q

Describe how uroporphyrinogen III is converted into Protoporphyrin IX

A

Uroporphyrinogen decarboxyalse catalyses the decarboxylation of four acetyl side chains to methyl groups to make coproporphyrinogen III. Coproporphyrinogen oxidase decarboxylates the two propionyl side chains to vinyl groups to form protoporphyrinogen IX. Protoporphyrinogen oxidase removes six H atoms to form Protoporphyrin IX

23
Q

Where are Uroporphyrinogen decarboxylase, coproporphyrinogen oxidase and protoporphyrinogen oxidase located?

A

Uro is in the cytosol, the other 2 are in the mitochondrial matrix

24
Q

how is Protoheme IX made?

A

ferrochelatase inserts Fe 2+ into protoporphyrin IX in the mitochondria.

25
Q

Where does ALA synthase work?

A

In the mitochondria

26
Q

Where are the two main sites of heme biosynthesis?

A

The liver and erythroid cells (85%)

27
Q

What is heme used for in the liver?

A

Cytochrome P450s important oxidative enzymes involved in detoxification.

28
Q

Describe heme synthesis in erythroid cells?

A

It happens mainly once in their life and heme is a positive feedback process.

29
Q

How does the liver tend to regulate Heme synthesis? inhibited and induced?

A

By targeting ALA synthase. This step is feedback inhibited by heme (repression of mRNA synthesis, inhibition of translation of ALA mRNA, inhibition of import into the mitochondira, direct inhibition of the enzyme) heme synthesis is induce by toxins or substances that also induce cytochrome P450 (TYLENOL-acetaminophen)

30
Q

Why shouldnt you take Tylenol for a hangover?

A

becasue alcohol induce P450 synthesis. Acetominophen is broken down by P450 into hepatotoxic stuff.

31
Q

What are porpyrias? What is their inheritance pattern?

A

genetic deficiencies in heme metabolism. Enzymes are usually partially defective because fully defective would be lethal. (dominant inheritance due to haploid insufficiency)

32
Q

What is a major difference between hepatic porphyrias and erythopoietic porphyrias?

A

Hepatic are specific for the liver and attacks are generally induced, meaning under normal circumstances they work sufficiently. Erythropoietic are are chronic conditions.

33
Q

describe the defect and symptoms of Congenital erythropoietic porphyria. What builds up?

A

deficiency in Uroporphyrinogen III cosynthase leads to build up of Uro I and copro I. this causes anemia and the skin is photosensitive such that it ulcerates and forms disfiguring scars, red urine, teeth turn reddish brown and increased hair growth

34
Q

Describe the defect and symptoms of Protoporphyria and compare its severity to congenital erythopoietic porphyria. What build up?

A

Defect in ferrochelatase causes build up of copro III and symptoms similar to, but less severe than CEP

35
Q

Describe the defect and symptoms of acute intermittent porphyria. What builds up?

A

affects the liver. and is the most common porphyria. caused by partial deficiency of porphobilinogen deanimase (uroporphyrinogen synthase) under normal conditions you are fine, but when liver is stressed ALA and porphobilinogen build up. Abdominal pain, vomiting, diarrhea, neuro, red urine

36
Q

Describe the defects and symptoms of Porphyria cutanea tarda. What builds up? how can you treat it?

A

deficiency in uroporphyrinogen decarboxylase (sporadic or autosomal dominant but may be multifactorial) Asymptomatic until liver disorder is imposed, photosensitivity, can be casued by behavioral factors or environmental. Uro III builds up. depletion of the bodies iron stores often leads to remission of symptoms.

37
Q

What is porphyrin? what is porphyrinogen?

A

Porphyrin- oxidized tetrapyrrole

porphyrinogen - reduced tetrapyrrole

38
Q

What is a hallmark sign for sensitivity to the sun

A

Erythropoietic porphyrias

MCP (5 decks)

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