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CPR Final > Erythrocyte Biochemistry > Flashcards

Erythrocyte Biochemistry Flashcards

1
Q

when is the majority of the Hb synthesized?

A

before the extrusion of the nucleus from the normoblast

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2
Q

what does the normoblast become when the nucleus is extruded?

A

a reticulocyte

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3
Q

what is the composition of fetal hemoglobin?

A

alpha2 gamma2

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4
Q

what is the composition of adult hemoglobin?

A

either alpha2beta2 or alpha2delta2

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5
Q

what happens to the iron in heme once the O2 binds to it?

A

there is a conformational change in the Hb; the iron moves into the plane of porphyrin in heme

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6
Q

what effect does the conformational change of the hemoglobin have?

A

it pulls down the proximal histidine of Hb and changes the interaction with the associated globin chain

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7
Q

what effect does 2,3-BPG have on Hb?

A

it reduces the O2 affinity so the Hb gives up more O2 to the tissues

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8
Q

what is the Bohr effect?

A

the stimulation of O2 release by CO2 and H+

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9
Q

what is the relationship between CO2/H+ and Hb?

A

they are allosteric effectors

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10
Q

what does the fetus require in regards to Hb?

A

the fetus needs Hb that has higher affinity for O2 than maternal Hb

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11
Q

how does the fetal Hb have a higher affinity for O2 than the maternal Hb?

A

the fetal Hb does not bind well to 2,3-BPG

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12
Q

what causes sickle cell anemia?

A

mutation at amino acid position #6 in the beta globin

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13
Q

what is the effect of the mutation that causes sickle cell anemia?

A

the glutamic acid changes to valine

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14
Q

what is currently being researched to treat sickle cell anemia?

A

induction of expression of HbF- using hydroxyurea

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15
Q

where is iron stored?

A

in cells that line the intestines, liver, spleen, and bone marrow

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16
Q

how is iron stored?

A

it binds to a protein-ferritin- as Fe3+

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17
Q

what is a product of ferritin breakdown?

A

hemosiderin

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18
Q

how is Fe2+ converted to Fe3+?

A

ferroxidase (aka cerruloplasmin)

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19
Q

how is Fe3+ converted to Fe2+?

A

ferric reductase (aka DCYTB)

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20
Q

what does ferric reductase (aka duodenal cytochrome B) require?

A

vitamin C

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21
Q

how does Fe2+ enter the enterocyte?

A

via the divalent transporter 1 (DMT1)

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22
Q

how is Fe2+ exported out of the enterocyte?

A

via ferroportin

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23
Q

what does ferroportin require in order to function?

A

Hephaestin

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24
Q

what are ferroportin levels regulated by?

A

Hepcidin

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25
Q

how is iron transported in the blood to target tissues?

A

as Fe3+ and bound to transferrin

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26
Q

how does uptake of transferrin occur?

A

receptor-mediated endocytosis via transferrin receptor

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27
Q

how is the transferrin internalized?

A

via clathrin coated pits into endosomes

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28
Q

how does the transferrin get released from its receptor once in the endosome?

A

the low pH of the endosome releases the transferrin

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29
Q

where does the endosome transiently dock?

A

on the mitochondria

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30
Q

how does the iron get to the mitochondria?

A

via DMT1

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31
Q

How is iron content in the body regulated?

A

by modulating its absorption- through Hepcidin

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32
Q

What happens when hepcidin binds to ferroportin?

A

it causes the internalization of ferroportin and its subsequent degradation in lysosomes

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33
Q

what could cause iron deficiency?

A

overuse of aspirin or ulcers of the GI tract

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34
Q

what does iron deficiency cause?

A

hypochromic microcytic anemia

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35
Q

What is the disease of iron overload?

A

hereditary hemochromatosis (or HH)

36
Q

where does iron accumulate in cases of hereditary hemochromatosis?

A

heart, liver, and pancreas

37
Q

what does hereditary hemochromatosis lead to?

A

liver cirrhosis, hepatocellular carcinoma, diabetes, arthritis, and heart failure

38
Q

what causes hereditary hemochromatosis?

A

autosomal recessive; mutations in the hereditary hemochromatosis gene (HFE)

39
Q

what is the typical body iron found in a patient with hereditary hemochromatosis?

A

15 g

40
Q

what is RBC production dependent on?

A

folate and vitamin B12

41
Q

why does megaloblastic macrocytic anemia occur?

A

occurs due to diminished synthesis of DNA in developing RBC in blood marrow

42
Q

what does a blood smear of a patient with megaloblastic macrocytic anemia show?

A

macrocytic normochromic cells

43
Q

what does the bone marrow of a patient with megaloblastic macrocytic anemia show?

A

large erythroblasts (megaloblasts) and hyper-segmented neutrophils

44
Q

Folic acid has three parts. What are they?

A

pteridine ring, PABA, and glutamate residue

45
Q

Folate can be reduced to what?

A

dihydrofolate (DHF)

46
Q

what enzyme is responsible for folate–> DHF?

A

DHF reductase

47
Q

what can DHF be reduced to and by what enzyme?

A

THF; by THF reductase

48
Q

what is the active form of folate?

A

THF

49
Q

what is THF important for?

A

synthesis of purines and the pyrimidine thymine; vital role in DNA synthesis

50
Q

DHF is found in most foods like what?

A

liver, eggs, milk, legumes, wheat, leafy veggies

51
Q

where is folic acid absorbed?

A

in the small intestine (jejunum)

52
Q

where can folate be stored and for how long?

A

the liver stores 5-10 mg of folate for 3-6 months

53
Q

once absorbed in the intestine, what is DHF converted to?

A

N5-methyl-THF (the primary circulating form of THF in the bloodstream)

54
Q

what is methotrexate?

A

an antineoplatic agent; inhibitor of DHF reductase-therefore inhibitor of DNA synthesis

55
Q

what happens if vitamin B12 is not available?

A

then folate is stuck as N5-methyl-THF–> the folate trap

56
Q

what is the action of vitamin B12?

A

it removes a methyl group from N5-methyl-THF to make methyl-cobalamin and release THF

57
Q

how do you get vitamin b12?

A

animal products

58
Q

what are most cases of B12 deficiency caused from?

A

a lack of intrinsic factor

59
Q

what does b-12 bind to?

A

R-binder proteins

60
Q

what is the intrinsic factor-cobalmin complex carried by in the blood?

A

transcobalamin II

61
Q

what is the gold standard of testing for pernicious anemia?

A

schilling test

62
Q

what is the structure of heme like?

A

there are 4 five-membered rings containing nitrogen and iron is present in the ferrous state

63
Q

where does the biosynthesis of heme primarily occur?

A

in the liver and the erythroid cells of bone marrow

64
Q

How many phases are there of heme biosynthesis and where do they occur?

A

3 phases; phase 1: mitochondria, phase 2: cytosol, phase 3: mitochondria

65
Q

defects in one or more stages of the heme biosynthesis cause what?

A

porphyrias

66
Q

What occurs during the first stage of heme biosynthesis?

A

succinyl CoA and glycine are formed together to form amniolevulinic acid

67
Q

what enzyme is responsible for phase 1 of heme biosynthesis?

A

ALA synthase

68
Q

what inhibits ALA synthase?

A

heme and hemin

69
Q

what does ALA synthase require and what happens if there is a deficiency of this?

A

ALA synthase requires vitamin B6 (PLP); if there is a deficiency of vitamin B6 there will be anemia

70
Q

lead inactivates 2 important enzymes in the heme biosynthesis pathway. What are these 2 enzymes?

A

ALA dehydratase and ferrochelatase

71
Q

what does lead poisoning lead to?

A

neurological symptoms (ALA builds up and is neurotoxic) and microcytic and hypochromic anemia; also impacts ATP synthesis

72
Q

there are two different types of porphyrias, what are they?

A

acute hepatic (cause neurological symptoms) and erythropoietic (affect skin and photosensitivity)

73
Q

what porphyria do you get when the prophobilinogen deaminase enzyme is defective?

A

acute intermittent porphyria (hepatic)

74
Q

what porphyria do you get when the uroporphyrinogen III cosynthase enzyme is defective?

A

congenital erythropoietic porphyria (erythropoietic)

75
Q

what porphyria do you get when the uroporphyrinogen III decarboxylase enzyme is defective?

A

porphyria cutanea tarda (hepatoerythropoietic)

76
Q

what porphyria do you get when the protoporphyrinogen oxidase enzyme is defective?

A

variegate porphyria (hepatic)

77
Q

what is the most common porphyria in the united states?

A

porphyria cutanea tarda

78
Q

what does congenital erythropoietic porphyria result in a build up of?

A

uroporphyrinogen I and its oxidation product uroporphyrin I

79
Q

what are the clinical signs of congenital erythropoietic porphyria?

A

red color in urine, red teeth, skin photosensitivity

80
Q

when RBCs are broken down, hemoglobin is released in large quantities. How is this handled?

A

by the reticulo-endothelial system

81
Q

what is globin broken down into?

A

amino acids

82
Q

what is heme converted to?

A

biliverdin

83
Q

what enzyme converts heme into biliverdin?

A

heme oxygenase

84
Q

what is biliverdin converted into?

A

bilirubin

85
Q

what enzyme convert biliverdin into bilirubin?

A

biliverdin reductase

CPR Final (9 decks)

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