Erythrocyte Biochemistry Part 1

Question 1

Process of Erythropoiesis

Answer 1

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

Question 2

what are the hemoglobin chains in adults and fetal and when do the chains begin to switch

Answer 2

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

Question 3

what is the structure of the adult hemoglobin

Answer 3

Multi-subunit

• 2 alpha globin chains
• 2 Beta globin chains

heme

• one per unit
• iron in ferrous form Fe+2
• carries O2
• Hydrophobic

Question 4

what is the confirmational change when Hb binds oxygen

Answer 4

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

Question 5

what is the difference between the myoglobin and hemoglobin oxygen dissociation curves (ODC)

Answer 5

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

Question 6

how does positive cooperativity work

Answer 6

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

Question 7

How does pH affect the ODC

Answer 7

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

Question 8

how does 2,3 BPG affect the ODC

Answer 8

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

Question 9

how does excersise affect the ODC

Answer 9

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

Question 10

what is important about the fetal HbF vs the mothers HbA RBCs

Answer 10

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)

Question 11

Sickle cell anemia

Answer 11

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

Question 12

Facts of Fe

Answer 12

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

Question 13

where is Fe stored and what is ferritin and Hemosiderin

Answer 13

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

Question 14

Process of Iron absorption, storage and transport and the two types of digested iron

Answer 14

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

Question 15

how do the Transferrin get iron into the cell

Answer 15

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

Question 16

How is the regulation of Iron done, what is the situation when iron is high vs low?

Answer 16

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

Question 17

Iron deficiency

Answer 17

insufficent dietary iron, insufficent absorption

caused by excessive blood loss, asprin, ulcers of GI tract

causes, hypochromic microcytic anemia

treatment: dietary iron supplementation

Question 18

Iron overload

Answer 18

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

Question 19

what are the two vitamins needed for RBC production and what happens if their is a deficiency

Answer 19

folate (folic acid) and vitamin B2 (cobalamin)

deficiencies in both lead to megaloblastic anemia

diminished synthesis of DNA

Question 20

Megaloblastic Macrocytic Anemia characteristics

Answer 20

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

Question 21

what are the three parts if Folate

Answer 21

Pterdine Ring
PABA
GLutamate

exists in a number of deratives collectively known as folates

Question 22

Folate Metabolism

Answer 22

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

Question 23

What does a folic acid deficiency lead to

Answer 23

leads to decreased DNA synthesis which can lead to megaloblastic macrocytic anemia

Question 24

how is folate absorbed

Answer 24

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

Question 25

what are the carbon sources for folate

Answer 25

serine, glycine, choline, histidine, formate

Question 26

how does vitamin B 12 play a factor in folate metabolism

Answer 26

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)

Question 27

what is Methotrexate and its function

Answer 27

antineoplastic agent

-inhibitor of DNA synthesis by inhibiting dihydrofolate reductase

Question 28

Process of B12 absorption

Answer 28

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

Question 29

Pernicious Anemia

Answer 29

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

Question 30

Schilling test

Answer 30

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