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MCM Exam II > Erythrocyte Biochemistry > Flashcards

Erythrocyte Biochemistry Flashcards

1
Q

When is the majority of Hb synthesized in the RBC

A

Before extrusion of nucleus from the RBC

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2
Q

A small amount of hemoglobin is made in the ____

A

Reticulocyte

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3
Q

What form is iron in when in hemoglobin

A

Ferrous form (Fe2+)

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4
Q

What are the two chain subunits in hemoglobin

A

2 Alpha-globin chains

2 Beta-globin chains

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5
Q

Three parts of embryonic hemoglobin

A

Hb Gower 1
Hb Gower 2
Hb Portland

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6
Q

When is the embryonic hemoglobin destroyed to make way for fetal hemoglobin

A

8-10 weeks

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7
Q

Difference between fetal Hb and adult Hb

A

Fetal
- HbF (alpha 2, gamma 2)
Adult
- HbA (alpha 2, beta 2)

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8
Q

When does the gamma chain of Hb dissolve and the beta chain begin

A

At birth

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9
Q

How can fetal hemoglobin be used to treat sickle cell?

A

The defect leading to sickle cell is in the beta chain hemoglobin in adult cells. Research uses hydroxyurea to induce HbF, which consists of alpha and gamma chains but not beta.

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10
Q

Downside of inducing HbF to treat sickle cell

A

Hydroxyurea is a toxic chemotherapeutic agent

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11
Q

F8 Histidine

“Proximal histidine”

A

Is bound to heme; stabilizes hemoglobin

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12
Q

E7 Histidine

“Distal Histidine”

A

Stabilizes O2 on hemoglobin; the oxygen binds to the iron that is between the heme and the distal histidine

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13
Q

What conformational change occurs in heme after binding of oxygen

A

It changes the position of iron in the plane of the heme
- changes the 0.4 A angle which pulls down the proximal F8 histidine and changes the interaction with associated globin chain

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14
Q

What kind of dissociation curve is associated with myoglobin

A

Hyperbolic curve

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15
Q

What kind of oxygen dissociation curve is associated with hemoglobin
- why

A

Sigmoidal curve

  • interactions between globin subunits
  • Hb switches between low and high affinity
  • the binding to O2 is reversible
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16
Q

Positive cooperativity in oxygen binding

A

Binding of one O2 to one heme facilitates the binding of O2 to another heme
- Conformational change in one globin subunit induces change in another

Binding of O2 to Fe of a globin subunit pulls proximal F8 histidine down
—> pulls on the globin FG-helix which changes interaction with other globin change

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17
Q

Bohr Effect

A

Decreasing the pH of actively respiring tissues (from increase in CO2) decreases the affinity of Hb for O2, which favors release of O2 to the tissues

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18
Q

Role of 2,3-BPG in hemoglobin binding

A

Reduces O2 affinity so Hb gives up more O2 to tissues

  • signals Hb to let go of O2
  • very high concentration in RBCs
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19
Q

How does exercise affect Hb and O2 binding

A

Exercise causes a drop in pO2 —> Hb has decreased affinity to O2 and releases it
- corresponds to the steepest part of sigmoidal O2 binding curve

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20
Q

HbF vs HbA in mother

A

Fetal hemoglobin has higher affinity for oxygen

- not regulated by 2,3-BPG

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21
Q

What molecule carries iron in the blood

A

Transferrin

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22
Q

Two proteins that store iron in the body

A

Ferritin (H2O soluble)

Hemosiderin (H2O insoluble)

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23
Q

What is the form of iron from animal products and plant products

A

Animal: ferrous
Plant: ferric

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24
Q

Ferric reductase

Dcytb- duodenal cytochrome-like b

A

Converts Fe3+ in non-heme iron to Fe2+

- uses calcium

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25
Q

Divalent transporter 1 (DMT1)

A

Takes up Fe2+ and transports it into the enterocyte

Also transports iron into the mitochondria in the TfR mediated endocytosis pathway

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26
Q

Ferroportin

A

Extrudes iron out of the cell

27
Q

Feroxidase/Hephaestin/cerruloplasmin

A

Converts free iron (Fe2+) to Fe3+ to be then carried by transferin

28
Q

Transferrin receptor (TfR)

A

Partakes in receptor mediated endocytosis to uptake transferrin into the cell –> transferrin enters cell to deliver iron to mitochondria

29
Q

Hereditary hemochromatosis

  • what is it
  • what mutation
  • symptoms
  • treatment
A

Organ dysfunction due to iron overload caused by dysregulation of iron uptake and export by enterocyte

  • Mutation: A. Recessive, HFE gene
  • Sx: cirrhosis, arthritis, endocrinopathy, skin pigmentation, cardiomyopathy
  • Tx: blood letting
30
Q

Hepcidin

A

Regulator of iron homeostasis
- binds to ferroportin which causes internalization of ferroportin which is then destroyed, thus stopping iron absorption

31
Q

Hepcidin expression and ferroportin levels when:

  • iron is high
  • iron is low
A

High iron:

  • high hepcidin
  • low ferroportin
  • iron absorption low

Low iron:

  • low hepcidin
  • high ferroportin
  • iron absorption high
32
Q

Mutations in Hfe (Human hemochromatosis protein) causes what

- mechanism

A

Hemochromatosis
- if Hfe is mutated then it cannot bind to TfR2, which means hepcidin expression cannot be turned on and ferroportin activity is uncontrolled
—> iron overloading

33
Q

RBC production is dependent on _____ and _____

A 
Vitamin b12 (cobalumin)
Folate (folic acid)
34
Q

Deficiency in vitamin B12 and folate can cause ______ due to _______

A

Megaloblastic anemia due to diminished synthesis of DNA in developing RBC in bone marrow

35
Q

characteristics of megaloblastic macrocytic anemia

  • erythrocyte volume
  • hemoglobin volume
  • color
  • bone marrow
A
  • large erythrocytes
  • normal hemoglobin
  • normochromic cells
  • bone marrow shows megaloblasts (large erythroblasts); hyper-segemented neutrophils
36
Q

Hyper-segmented neutrophils, megaloblasts, and large erythrocytes would indicate what disease:

A

megaloblastic macrocytic anemia

37
Q

3 parts of folic acid

A

pteridine (nitrogen containing ring)
p-amino-benzoic ring (PABA)
glutamate reside chains

38
Q

Dihydrofolate reductase

A

reduces folate –> dihydrofolate (FH2) and dihydrofolate (FH2) –> tetrahydrofolate (THF)

39
Q

DHF

A

dietary folic acid

40
Q

Tetrahydrofolate (THF) or (FH4)

  • what is it
  • what vital role does it play
A

active form of folate; transfers carbon units from donors to acceptors

  • serves vital role in DNA synthesis
  • –> adds methylene (CH2) in the synthesis of nucleotides (adds to dUMP to form dTMP)
41
Q

Folic acid pathway

- two carbon transfers

A

folate –> dihydrofolate –> tetrahydrofolate

  • main carbon transfer occurs when carbon side chain of serine is transferred to THF to form N5,10-methylene-THF
  • the carbon of N5,10-methylene-THF is then transferred to dUMP to form dTMP, during which DHF is made, which is then reduced to THF to start cycle again
42
Q

Purpose of vitamin B12 (cobalamin) in the folic acid pathway

A

folate is available as N5-methyl-THF, which will not give up single methylene group to dUMP to make dTMP for DNA synthesis; B12 demethylates N5-methyl-THF in order for it to enter the cycle as THF

43
Q

Folic acid deficiency leads to _____ which leads to ___

A

decreased DNA synthesis which leads to megaloblastic microcytic anemia

44
Q

how does the folic acid pathway aid in DNA synthesis

A

a carbon from N5,10-methylene-THF is transferred to dUMP which forms dTMP which can be used in DNA synthesis as thymine

45
Q

where is folate (DHF) found in food

A

most foods:

  • eggs
  • milk
  • yeast
  • leafy vegetables
46
Q

where is folic acid absorbed

A

in the small intestine (jejunum)

47
Q

once absorbed in the intestine, folic acid is reduced to

A

N5-methyl-THF

48
Q

what happens to the methyl group that B12 removes from N5-methylene-THF

A

it is transferred to homocysteine to create methionine via methionine synthase

49
Q

most deficiencies in B12 are due to lack of _____

A

intrinsic protein

50
Q

B12 absorption pathway

A

dietary B12 binds to R-binders –> proteases degrade R binders –> releases B12 –> intrinsic factors carry B12 to ileum where receptors bring it into body

51
Q

R binder proteins are made by ____

A

gastric mucosa cells

52
Q

intrinsic factor-cobalamin is taken up from the ileum by ___

A

receptor-mediated endocytosis

53
Q

cobalamin circulates the blood carried by

A

transcobalamin

54
Q

pernicious anemia

  • what is it
  • what causes it
A

megaloblastic macrocytic anemia
- deficiency in B12 resulting from unavailability of intrinsic factor (IF) which results from destruction of IF and the cells producing it (ex: auto-immune mechanism)

55
Q

Part one of Schilling Test

  • what is it
  • what do the results mean
A

patient is given oral dose of co-labeled B12 with an injection of unlabeled B12 cobalamin

  • if B12 is absorbed from the GI, it will pass into the urine
  • absent in urine = B12 not absorbed (possible pernicious anemia)
  • present in urine = normal absorption (dietary deficiency)
56
Q

Part two of Schilling Test

  • what is it
  • what do the results mean
A

if B12 was absent in the urine in part one, proceed to part two:
patient is given oral dose of co-labeled B12 PLUS intrinsic factor with an injection of unlabeled B12 cobalamin
- if radioactive B12 is present in urine, it means the absorption has improved, meaning the patient is deficient in intrinsic factor = patient has pernicious anemia

57
Q

erythropoiesis pathway

A

hemocytoblast (stem cell) –> proerythroblast (committed cell) –> early erythroblast –> late erythroblast –> normoblast –> reticulocyte –> erythrocyte

58
Q

what occurs in phase 1 of erythropoiesis

A

ribosome synthesis

59
Q

what occurs in phase 2 of erythropoiesis

A

hemoglobin accumulation

- being cranked out from ribosomes

60
Q

what occurs in phase 3 of erythropoiesis

A

ejection of nucleus and organelles

61
Q

characteristics of heme in hemoglobin structure

  • how many per subunit/how many total
  • what does it do
  • hydrophilic/hydrophobic?
  • has an atom of ____
A
  • 1 per subunit/4 total
  • carries oxygen
  • hydrophobic
  • iron (Fe2+)
62
Q

what is adult hemoglobin (HbA) made of

A

97% alpha2beta2

3% alpha2sigma2

63
Q

TfR mediated endocytosis pathway

A

transferin is internalized via clathrin coated pits (endosome) –> endosome transiently docks on the mitochondria and transfers iron directly to mitochondria –> DMT1 transports iron out of endosome

64
Q

where is heme made

A

in the mitochondria

MCM Exam II (14 decks)

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