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biochemistry > heme synthesis and regulation > Flashcards

heme synthesis and regulation Flashcards

1
Q

illustrate of porphyrin structure

A
  • 4 pyrrole rings linked by methenyl bridges (-CH)
  • form complex with metal ion ( Fe or Mg )
  • conjugate with protein to form hemoprotein
  • side chains of heme present in Hb (proto) : 2P propionyl , 2V vinyl & 4M methyl
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2
Q

illustrate the difference between heme and hemin

A
  • heme : ferrous iron (Fe +2 ) + protoporphyrin IX
  • hemin : “ hematin , oxidized heme “ ferric iron (Fe +3 ) + protoporphyrin
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3
Q

def of porphyrinogen

A

reduced ( hydrogenated ) porphyrin contain methylene (-CH2) not methenyl (-CH)

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4
Q

list types of hemeprotein and their function

A
  • Hb : transpor O2
  • myoglobin : storage O2 in muscle
  • cytochrome P450 : hydroxylation of xenobiotic as drugs
  • cytochrome C : in electron transport chain “ respiratory chain “
  • catalase : degradation of H2o2
  • cytoplasmic guanyl cyclase : formation of cGMP
  • tryptophan pyrrolase : oxidation of tryptophan
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5
Q

list the site of biosynthesis of heme

A

-all tissue ( except RBCs, no mitochondria) especially :
bone marrow ( erythrocytic )
liver ( non erythrocytic)

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6
Q

list the site of biosynthesis of heme

A

-all tissue ( except RBCs, no mitochondria) especially :
bone marrow ( erythrocytic )
liver ( non erythrocytic)

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7
Q

the reactions are ……….

A

irreversible

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8
Q

to produce one heme we need ….. & ……

A

8 glycine (AA)
8 succinyl CoA ( from TCA cycle )

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9
Q

heme biosynthesis begins and ends in ……
but 3 intermediate reactions occur in ……

A

mitochondria
cytoplasm

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10
Q

illustrate step of heme synthesis

A
  • in mitochondria :
    1. formation of δ ALA (by ala synthase)
    need pyridoxal phosphate “coenzyme of vit B6 “
  • in cytoplasm :
    2. add 2δ ALA to form porphobilinogen
    “ PBG” by ALA dehydratase “ PBG synthase “ release 2H2o
    ( inhibited by lead which replace zinc)
    3. condensation of 4 PBG to form first porphyrinogen
    4. modification of side chain ( uro - copro -proto )
  • in mitochondria:
    5. oxidation of the ring ( porphyrinogen to porphyrin )
    6. insertion of iron ( by ferro chelatase
    ( inhibited by lead )
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11
Q

rate limiting enzyme is ……..

A

ALA synthase
- there is 2 ALA synthase isomers :
ALAS1 in all tissue
ALAS2 in erythroid specific

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12
Q

what’s the importance of heme convert to hemin ( hematin ) ( Fe +2 toFe+3 ) ?

A
  • act as repressor at gene level “ not allosteric “
  • inhibit ALAS1 only transcription , dec stability of mRNA , and dec its import into mitochondria
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13
Q

inc activity of ALAS1 only in ……..
( how ?)

A

-liver ( derepression )
- by substance metabolized by cytochrome P450 ( steroids , barbiturates and insecticides )

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14
Q

in ……… ALAS2 is controlled by availability of intracellular …….

A

bone marrow
iron

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15
Q

………. increase activity of ALAS2 in erythropoietic tissues due to release of erythropoietin

A

hypoxia

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16
Q

what’s the nature of lesion :
porphyrias ( the vampire disease )

A

-rare group of genetic disorders of heme synthesis .
- result in the accumulation and inc excretion of porphyrins or porphyrin precursors

17
Q

list symptoms of the vampire dissease ( why called that )

A
  1. sensitive to sun light that can easily result in burns and abrasions
  2. they prefer darkness
  3. they suffer from acute attacks of abdominal pains and vomiting
  4. their urine purplish red color ( wrongly believe that it results from drinking blood )
  5. inc hair growth + repeated damage = skin tightens and shrinks
  6. canine teeth to be more prominent and suggistive of fangs
18
Q

list types of anemia

A
  • ala synthase 2 deficiency ( X linked sideroblastic anemia “ XLSA”
  • B6 deficiency ( ringed sideroblastic )
  • lead poisoning ( ringed sideroblastic)
  • sideroblasts are atypical nucleated erythrocytes with granules of iron accumulated in perinuclear mitochondria
19
Q

list enzyme affected in them

A
  • ALA synthase 2 deficiency = ALAS2
  • B6 deficiency= ALA synthase
  • lead poisoning = ALA dehydrates & ferrochelatase
20
Q

what happen to iron in them ?

A

increase in all of them

21
Q

list cause of each one

A
  • ALA synthase 2 deficiency = ALAS2 deficiency ( hereditary or congenital hypochromic anemia )
  • B6 deficiency= isoniazide drug for TB ( inhibit vit B6 )
  • lead poisoning = lead paints , batteries

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