Erythrocyte Biochemistry Part 1 Flashcards
Process of Erythropoiesis
Hemocytoblast (stem cell)
Proerythroblast (committed cell)
Early erythroblast (start of development pathway)
-ribosome synthesis
Late erythroblast
Normoblast
-hemoglobin accumulation
end of normoblast
-eject nucleus and organelles (mitochondria)
reticulocyte
Erythrocyte
Majority of Hb is synthesized before extrusion of nucleus from the normoblast to become a reticulocyte
-small amount is made in reticulocyte
what are the hemoglobin chains in adults and fetal and when do the chains begin to switch
Fetal: Hb F (2 alpha chains, 2 gamma chains)
Adult: Hb A (2 alpha chains, 2 beta chains) Hb A2 (2 alpha chains, 2 delta chains)
prior to birth the fetus will start to make more B chains, right after birth this significantly increases
also after birth the gamma chains begin to significantly decrease to zero
what is the structure of the adult hemoglobin
Multi-subunit
- 2 alpha globin chains
- 2 Beta globin chains
heme
- one per unit
- iron in ferrous form Fe+2
- carries O2
- Hydrophobic
what is the confirmational change when Hb binds oxygen
pulls down the proximal histidine of Hb and changes the interaction with associated globin chain
-iron moves into the plane of the heme
then the distal histidine stabillizes the bound oxygen
what is the difference between the myoglobin and hemoglobin oxygen dissociation curves (ODC)
Myoglobin has a hyperbolic curve
Hemoglobin has a sigmoidal curve due to the cooperativity and the irreversible binding
therefore hemoglobin has a lag phase and needs about 26torr of oxygen to get P50
how does positive cooperativity work
Hb binds O2 in a cooperative manner
binding of one molecule of O2 to one heme, facilitates the binding of an O2 to another heme
the first O2 is the hardest to bind to the heme
this is because when one O2 binds it causes a conformational change in another subunit making it easier to bind
How does pH affect the ODC
Bohr effect
-pH of actively respiring tissues is lower
-as pH decreases, binding affinity of Hb for O2 decreases
-Histidine will also pick up the the H+ from the tissue
leading to the Hb to favor release of O2
this is a rightward shift on the ODC graph
how does 2,3 BPG affect the ODC
2,3-BPG causes a shift to the right
it reduces the O2 affinity so Hb gives up more O2 to tissues
signal to the Hb to let go of O2
how does excersise affect the ODC
because of the drop in pO2 which brings the Hb saturation to the steepest part of the curve, the Hb is very effective in providing oxygen to exercising tissues
what is important about the fetal HbF vs the mothers HbA RBCs
the fetus heeds Hb to have a higher affinity for O2 than maternal Hb
therfore the fetal Hb can take the oxygen from the maternal Hb
O2 flows from mother to fetus
Hbf does not bind well to 2,3BPG therefore makes it have a higher affinity for O2 (a leftward shift)
Sickle cell anemia
mutation at amino acid in B-globin mking a glutamic acid (negative charge) changes to a valine (hydrophobic)
causes polymerization of hemoglobin giving a sickle shape in RBCs
leads to heomlytic anemia
-pain, organ damage, stroke, increased infections
ongoing research to induce HbF expression
use hyroxyurea to induce HbF
-works but causes inflammation, and is a toxic chemotherapeutic agent
Facts of Fe
exists as Fe2+ (ferrous) or Fe3+ (ferric ) state
plays a role in oxygen transport, and in electron transport chain
Iron is regulated by modulating its absorption
where is Fe stored and what is ferritin and Hemosiderin
Fe is stored in cells that line the intestines, liver spleen, and bone marrow
Ferritin: A protein that binds to ferric Iron
Hemosiderin: Product of ferritin breakdown
Process of Iron absorption, storage and transport and the two types of digested iron
Heme iron from animal (Fe +2) easily absorable, will enter the enterocyte and become oxidized by ferroxidase (cerruloplasmin)
-stored in the form of ferritin and its degradation product is homosiderin)
Non heme iron (Fe+3)(plant products) more difficult to absorb, converted to Fe2+ by ferric reductase by Dcytb (duodenal cytochrome-like b protein) in presence of Vitamin C
-enters the entercyte by divalent transporter-1 (DMT1)
either converted to Fe3+ for storage by ferroxidase or exported out of enterocyte by ferroportin
Ferroportin requires hephaestin for function
-regulated by hepcidin
once in blood Fe2+ is converted to Fe3+ by ferroxidase. gets bound to transferrin to transport to target tissue
how do the Transferrin get iron into the cell
does through mediated endocytosis
Transferrin binds the transferrin receptor and becomes internalized by the clathrin coated pits
the decrease in pH leads to release of transferrin from its receptor
the endosome will then dock on mitochondria and then transfer the iron directly to the mitochondria via the DMT1
How is the regulation of Iron done, what is the situation when iron is high vs low?
Iron content is regulated by modulating absorption through a peptide hormone called hepcidin
binding of hepcidin to ferroportin causes internalization of ferroportin and its subsequent degradation in lysosomes
iron is high: hepcidin expression is up, ferroportin levels down, iron absorption is low
iron is low: hepcidin expression down, ferroportin levels up, iron absorption high
Iron deficiency
insufficent dietary iron, insufficent absorption
caused by excessive blood loss, asprin, ulcers of GI tract
causes, hypochromic microcytic anemia
treatment: dietary iron supplementation
Iron overload
Hereditary Hemochromatosis (HH)
increased absorption of iron which then accumulates in heart, liver, and pancreas
causes liver cirrhosis, hepatocellular carcinoma, diabetes, arthritis, and heart failure
autosomal recessive
Hereditary hemochromatosis gene
treatment: blood letting and iron chelaters
15g of iron, normal 3-5g
what are the two vitamins needed for RBC production and what happens if their is a deficiency
folate (folic acid) and vitamin B2 (cobalamin)
deficiencies in both lead to megaloblastic anemia
diminished synthesis of DNA
Megaloblastic Macrocytic Anemia characteristics
caused by deficiency of folate and vitamin B12
characterized by large erythrocytes
MCV > 100fL
RBC volume increased
macrocytic normochromic cells
bone marrow show large erythroblasts (megaloblasts)
hyper segmented neutrophils
what are the three parts if Folate
Pterdine Ring
PABA
GLutamate
exists in a number of deratives collectively known as folates
Folate Metabolism
folate can be reduced by DHF (dihydrofolate reductase)
further reduced to THF (tetrahydrofolate) by dihydrofolate reductase
THF is active form and can be used to synthesis of purines and pyrimidines and DNA synthesis
What does a folic acid deficiency lead to
leads to decreased DNA synthesis which can lead to megaloblastic macrocytic anemia
how is folate absorbed
absorbed in the small intestine (jejunum)
liver stores 5-10 mg folate that can last up to 3-6 months
dietary presents as DHF
once absorbed in the intestine folic acid is reduced to N5-methyl-THF which is the primary circulating form
what are the carbon sources for folate
serine, glycine, choline, histidine, formate
how does vitamin B 12 play a factor in folate metabolism
Vitamin B 12 is required to transfer methyl group to make THF
if not have then folate is stuck as N4-methyl-THF: called the folate trap
removes the methyl group from the N5-methyl-THF to make methyl-cobalamin (B12-ch3) and release THF (FH4)
what is Methotrexate and its function
antineoplastic agent
-inhibitor of DNA synthesis by inhibiting dihydrofolate reductase
Process of B12 absorption
found in animal products, not plant
-B12 deficiences can lead to megaloblastic macrocytic anemia
085 percent of B12 deficiency is from the lack of a protein called intrinsic factor
Dietary B12 binds to R-binder proteins
intrinsic factor will degrade R-binder proteins in the duodenum and release B12 and carry it to ileum from where it is released into the bloodstream
then will be taken up in cells by receptor mediated endocytosis
Pernicious Anemia
Vitamin B12 deficiency
-can occur due to lack of intrinsic factor which is necessary for B12 absorption
this is megaloblastic macrocytic anemia
failure to absorb vitamin B12 resulting from unavailabillity of intrinsic factor
test serum B12 and folate
then if B12 use the schilling test to determine how its affected
Schilling test
giver oral dose of tracer B12 and an injection of lots of unlabeled B12 to saturate the receptors in the liver
therefore the body will absorb the tracer B-12 and then pass to urine
if B12 is not absorbed and not in urine = pernicious anemia
if B12 is there then there is a B12 deficiency in the diet
part 2 of this is do the same but also with intrinsic factor as well to determine if pernicious anemia is due to a lack of intrinsic factor
