Erythrocyte Biochemistry

Question 1

What makes R-Binder proteins?

Answer 1

Gastric mucosa cells in the stomach

Question 2

Where does nonheme iron come from?

Answer 2

Plant products

Question 3

Oxygen Dissociation curve for hemoglubin

Answer 3

Sigmoidal curve

Question 4

The uptake of transferin by cells is done by what process?

Answer 4

Receptor mediated endocytosis via transferin receptor (TfR).

Question 5

B¹² deficiency is often caused by what.

What impact can this deficiency have?

Answer 5

Dietary lack is not often the cause, 3 ug dailly allowance

85% of cases are the lack of a protein called intrinsic factor.

Causes megaloblastic anemia because of the decrease of N^5,10-methylene-THF and on DNA synthesis

Question 6

What is the efficiency of hemoglobin in delivery of oxygen to from lung to tissue.

Answer 6

Drops from 7.4 to 7.2 pH

66%

Question 7

Describe B12 Absorbtion

Answer 7

B12 binds to R-binder proteins in somach

Degraded by proteases in the dudenom releasing B12

Intrinsic factor carries B12 to ileum where it is absorped by receptors.

Question 8

In what form foes ferritin store iron?

Answer 8

As Fe3+

Question 9

What converts Fe3+ in non-heme iron to Fe2+

Answer 9

Ferric Reductase

Question 10

What is the generation of erythrocytes known as?

Answer 10

Erthropoiesis

Question 11

Where does heme iron come from?

Answer 11

Animal products

Question 12

Why is HbF in the fetus higher in affinity the HbA in the mother?

Answer 12

Oxygen travels mother to fetus.

HbF does not bind well to 2,3-BPG so this cannot decrease its affinity as much.

Question 13

What happens to affininty for oxygen as pH decreases. How does this work and what is this effect called?

Answer 13

O₂ affinity decreases as pH decreases

His 146 picks up H+ from tissue and causes a conformational change in Hg.

Called the Bohr Effect

Question 14

How do internalized endosomes get transferin to the mitchondira for heme synthesis?

Answer 14

Clatherin coated endosome transiently docks and DMT1 helps to facilitate the transport of iron out of the endosome.

Question 15

2,3-Biphosphoglycerate has what effect on O2?

Answer 15

Reduces the affinity of O2 so Hb gives up more O2 to tissues

Question 16

What form of folate is dietary?

Answer 16

Dihydrofolate (DHF)

Question 17

What is portential therapy for sickle cell anemia?

What are the worries in this?

Answer 17

Changing HbS to HbF using hydroxyurea

This is a toxic chemotherapeutic agent

Question 18

What cell features are observed in megaloblastic anemia?

Answer 18

Large erythrocytes >100 fL (normal is 80-100) (same ratio of hematocrit)

Large erythroblasts

Hyper-segmented neutrofills (more then 5 lobes, 3-4 normal)

Question 19

How is B12 transported into and throughout the blood

Answer 19

Intrinsic factor bound to cobalin is taken up by receptor-mediated endocytosis.

Cobalin circulates through the blood by transcobalamin

Question 20

Stem cells and commited cells of erthropoiesis

Answer 20

Hemocytoblast

Proerythroblast

Question 21

What can result as part of Hereditary Hemochromatosis?

Answer 21

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

Question 22

What is the function of THF?

Answer 22

Transfers carbon units from donors to acceptors

Is vital for DNA synthesis

Question 23

What transports iron in the blood?

Answer 23

Transferrin

Question 24

What enzyme refuces folate to DHF and THF?

Answer 24

Dihydrofolate reductase

Oxidizes NADPH to NADP

Add 2 electons + hydrogens at a time

Question 25

Describe folate metabolism.

Answer 25

**THF to N^5,10-methylene-THF** as the carbone side chain of a serine is transfered Carbon of **N^5,10-methylene-THF** is transfered to deoxyuridylate (**dUMP**) to form deoxythmidylate (**dTMP**) during which **DHF is made**

Question 26

How does positive cooperativity work?

Answer 26

The binding of O₂ to Fe of a globin subunit pulls the proximal F8 histindine down ==\> this pulls the globin FG-helix and changes the interaction with the other globin chain in Hb

Question 27

What converts free iron to Fe3+?

Answer 27

Hephaestin/cerruplasmin

Question 28

Dysregulation of iron uptake and export by enterocyte 15g of Total iron body weight What is the disease and treatment?

Answer 28

Hereditary Hemochromatosis Blood letting

Question 29

What is the fetal hemoglubin and when does it peak?

Answer 29

Hb F (a2g2) Gamma chain peaks right before birth and then subsides. Alpha continually increases up untill birth where it levels off.

Question 30

What makes Intrinsic factor?

Answer 30

Pariatal cells in the stomach.

Question 31

How does regulation of hepciden work?

Answer 31

Tf-Fe bind s Tfr1 This causes Hfe to bind to Tfe2 Tf2 then upregulats signal transduction of hepcidin

Question 32

What takes up Fe2+ in the enterocyte.

Answer 32

Divalent transporter-1 (DMT1)

Question 33

What percentage of Iron is stored and in what forms?

Answer 33

27% ## Footnote **Ferritin and hemosiderin**

Question 34

What takes Fe 2+ out of the cell?

Answer 34

Ferroportin

Question 35

How is pernacious anemia tested?

Answer 35

Serum folate \<3 ng/ml Serum B12 \<350pg/ml Coduct Schilling Test

Question 36

Distal hisitidine location. What does it stabilize binding of?

Answer 36

E7 binds to the iron between the heme and distal histidine Binds with oxygen.

Question 37

How does the comformation of hemoglubin change when oxygen bind?

Answer 37

A 0.4 Å change pulls down the proximal F8 histidine of Hb and changes interaction with associated globin chain

Question 38

What would a mutation in Hfe cause?

Answer 38

Hemotomachromatosis Can no longer bind to Tf2 and cause upregulation of hepcidin, therefore it would lead to overload of iron in blood

Question 39

Oxygen Dissociation curve for **Myoglubin**

Answer 39

**Hyperbolic curve**

Question 40

Why is cobalamin essential to overcoming the folate trap?

Answer 40

Vitamin B12 removes a methyl group from N⁵-methyl-THF to make methyl-cobalalmin (B12-CH₃) and THF

Question 41

How do you conduct the Schilling test?

Answer 41

0. 5-1.0 ug oral dos of ⁵⁷Co-labled B12 (simultaneously saturating all cobalim receptor s with 1,000ug injection of B12). 1. If radioactive urine after 24 hours = healthy and diet is the problem (STOP) 2. If not radioactive urine after 24 hours = pernacious anemia (GO ON TO 3.) 3. Repeat with B12 doses given with Intrinsic factor, if radioactive its due to a lack of intrinsic factor.

Question 42

What are the adult hemogblubins

Answer 42

Hb A (a2b2) 97% Hb A2 (a2g2) 3% Beta increases more rapidly after birth and to a greater degree then gamma

Question 43

What are the embryonic hemeglobins and when are they gone?

Answer 43

Hb Gower 1 Hn Gower 2 Hb Portland

Question 44

What are the tetramer chains in Hemoglubin

Answer 44

2 alpha-globin chains 2 beta-globin chains

Question 45

What is added to THF to create a C-FH₄ donor?

Answer 45

Addition of CH₂

Question 46

Where is folate absorbed and where is it absorbed?

Answer 46

**The jejunum** **Liver stores 5 to 10 mg folate which can last 2 to 6 months**

Question 47

Peptide that binds to ferroportin causing internalization and proteolysis of ferroportin. Explain it's regulation of iron homeostasis

Answer 47

Hepcidin Iron High = Hepcidin Up = Ferroportin Down

Question 48

Steps of the developmental pathway in erythropoeisis.

Answer 48

Early erythroblast -\> Late erythroblast (Ribosome synthesis) Late erythroblast -\> Normoblast (Hemeoglubin accumulation) Normoblast -\> Retulocytes (Ejection of nucleus) Retulocytes -\> Erythrocytes

Question 49

What does hepcidin overexpression result in? What about underexpression?

Answer 49

Low plasma iron levels Overloaded plasma iron levels.

Question 50

What causes **hypochromic microcytic anemia?**

Answer 50

_Iron Defieciency_ Insufficient dietary iron Menstration Aspirin overuse Ulcers of GI tract (Blood loss) **Treatment - dietary iron supplementation**

Question 51

Why is B12 needed in folate acid metabolism?

Answer 51

N⁵-methyl-THF requires **cobalamin** to transfer a single methylene group to dUMP to make dTMP (for DNA synthesis) Stuck as N⁵-methyl-THF known as **the folate trap**

Question 52

Where is the proximal hisitidine located at?

Answer 52

F8 Histidine bound to heme

Question 53

What can HbS cause in hemoglubin?

Answer 53

Polymerization

Question 54

Why is methene-THF important and what does it do?

Answer 54

Synthesis of nucleotides through addition of methylene THF grabs methyl groups using 2 Nitrogens

Question 55

What reduces Fe3+ to Fe2+ on cell surface?

Answer 55

Dcytb (**duodenal cytochrome b**) aka **Ferric Reductase**

Question 56

What is a healthy iron body weight

Answer 56

3 to 5g

Question 57

What is pernacious anemia

Answer 57

Lack of intrinsic factor results in megaloblastic macrocytic anemia due to lack of B12. Results in: Gastric mucosa destroyed through auto-immune mechanism Decreased intrinsic factor

Question 58

How does RBC production depend of folate and B12

Answer 58

It does so for DNA synthesis. If there is a decrease in this it can result in **megaloblastic anemia.**