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MCM test 2 > Erythrocyte Biochem > Flashcards

Erythrocyte Biochem Flashcards

1
Q

Erythropoiesis

A

-starts as stem cell
• Majority of Hb synthesized before extrusion of nucleus
• Small amount made in reticulocyte

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2
Q

hemoglobin structure

A

• Multi-subunit
protein (tetramer)
– 2 a-globin chains
– 2 b-globin chains

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3
Q

heme

A 
– One per hemoglobin subunit
– Has iron atom
(ferrous : Fe2+)
– Carries O2
– Hydrophobic
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4
Q

Embryonic hemoglobin

A

Hb Gower 1 (]2epislon2)
Hb Gower 2 (a2epsilon2)
Hb Portland (]2gmma2)

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5
Q

fetal hemoglobin

A

Hb F (a2gamma2), 0.5%

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6
Q

adult hemoglobin

A 
Hb A (a2b2), 97%
Hb A2(a2G2), 3%
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7
Q

what are chains of hemoglobin derived from?

A

diff genes located on diff chromosomes (16 and 11)

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8
Q

treatment for sickle cell anemia

A

induce expression of HbF
using hydroxyurea
but this is a toxic
chemotherapeutic agent

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9
Q

what is the proximal histidine

A

The F8 histidine (bound to heme)

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10
Q

what is the distal histidine

A

The E7 histidine

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11
Q

where does O2 bind?

A 
binds to
the iron
between the
heme and distal
histidine
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12
Q

what is the conformation change when O2 binds?

A

pulls down the proximal F8 histidine of Hb and

changes interaction with associated globin chain

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13
Q

what kind of curve is myoglobin

A

hyperbolic

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14
Q

what kind of curve is hemoglobin

A

sigmoidal (due to interactions between globin subunits)

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15
Q

positive cooperativity

A
  • Binding of one molecule of O2 to one heme, facilitates the
    binding of an O2 to another heme
    -Conformational change in one globin subunit induces a
    conformational change in another subunit in Hb
  • The binding of O2 to Fe of a globin subunit pulls the proximal
    F8 histidine down
  • This pulls on the globin FG-helix and changes the interaction
    with the other globin chains in Hb
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16
Q

Bohr Effect

A

decrease in Ph causes binding affinity of Hb for O2 to decrease (right shift)
-causes release of o2

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17
Q

2,3-BPG

A
  • causes right shift

- reduces O2 affinity so Hb gives up more O2 to tissues

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18
Q

effects of o2 on ODC

A

drop in P02 from 40 to 20 torr

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19
Q

why does HbF have higher O2 affinity than HbA

A

Hbf does not bind well to 2,3 BPG therefore has higher affinity for O2

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20
Q

in what form is iron stored?

A

Fe 3+ (ferric)

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21
Q

in what form is iron transfered in blood

A

Fe3+

22
Q

how does nonheme iron enter enterocyte?

A

ferric reductase converts to Fe2+

-Fe 2+ enters enterocyte through divalent transporter-1(DMT1)

23
Q

what converts Fe 2+ to Fe 3+

A

hephaestin/ cerruloplasmin/ ferroxidase

24
Q

what converts Fe 3+ to Fe 2+

A

Dcytb (duodenal cytochrome like B) aka ferric reductase

25
Q

what allows Fe2+ to go from enterocyte to blood

A

ferroportin

26
Q

how is transferin uptaken from blood?

A

occurs by receptor-

mediated endocytosis via transferin receptor (TfR)

27
Q

what transports iron out of edosome?

A

DMT1

28
Q

what causes Causes hypochromic microcytic anemia

A

Insufficient dietary iron
Menstruating women
Aspirin overuse
Ulcers of GI tract (Blood loss)

29
Q

what is treatment for hypochromic microcytic anemia

A

dietary iron supplementation

30
Q

Hereditary Hemochromatosis

A

Organ dysfunction due to iron overload: cirrhosis, arthritis, endocrinopathy, skin pigmentation, cardiomyopathy

31
Q

what is total body iron inHereditary Hemochromatosis compared to normal

A

› 3 to 5g normal

› Hereditary Hemochromatosis = 15g

32
Q

Hepcidin

A

binds to ferroportin and causes internalization

-regulates amount of Fe taken up by body

33
Q

how is hepcidin expression regulated

A

by Hfe binding to TfR2

34
Q

what happens if Hfe is mutated and can’t bind to TfR2

A
  • cant turn on hepcidin expression
  • lots of ferroportin
  • iron overloading
35
Q

what vitamins are required for RBC production

A 
vitamin B12 (cobalamin) and
folate (folic acid)
36
Q

what does deficiency in B12 and folate cause?

A

megaloblastic anemia

-due to diminished synthesis of DNA

37
Q

Megaloblastic Macrocytic Anemia

A

Caused by vitamin B12 (cobalamin) and folate (folic acid)
deficiency
Characterized by large erythrocytes
› MCV >100 fL (as high as 140 fL); normal = 80-100
**NORMAL HEMOGLOBIN CONTENT

38
Q

what disease to hyper-segmented neutrophils occur?

A

Megaloblastic Macrocytic

Anemia:

39
Q

what is the structure of folate?

A

3 parts:
– Pteridine: nitrogen containing ring
– p-amino-benzoic acid ring (PABA)
– Glutamate residue chains

40
Q

what is the active form of folate?

A

THF (FH4) (tetrahydrofolate)

41
Q

what is the role of THF (FH4)(tetrhydrofolate)

A

transfer of carbon units from donor to acceptors (vital role in DNA synthesis)

42
Q

what is the form of dietary folic acid?

A

FH2 (dihydrofolate)

43
Q

where is folate absorbed

A

small intestine (jejunum)

44
Q

what organ stores folate?

A

liver

-stores 5-10 mg folate lasts 3-6 months

45
Q

what is primary circulating form of folate?

A

N5-

methyl-THF

46
Q

what happens if B12 not available for folate?

A

folate stuck
as N5-methyl-THF : called the folate
trap

47
Q

what does vit b12 do to folate?

A

removes methyl group from N5-methyl-THF to

make methyl-cobalamin (B12-CH3) and release THF (FH4)

48
Q

what does dietary B12 bind to?

A

R-binder proteins made by gastric mucosa cells

49
Q

what carries b12 to ileum

A

intrinsic factor made by parietal cells of stomach

50
Q

Pernicious Anemia

A

Vitamin B12 deficiency can occur due to lack of intrinsic factor
(necessary for B12 absorption)
- ms a megaloblastic macrocytic anemia

51
Q

how is pernicious anemia diagnosed

A

schilling test

MCM test 2 (16 decks)

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