10. Erythrocyte Biochemistry

Question 1

What are the seven stages of erythrocyte differentiation?

Answer 1

1. Hemocytoblast
2. Pro-erythroblast
3. Early Erythroblast
4. Late Erythroblast
5. Normoblast
6. Reticulocyte
7. Erythrocyte

Question 2

At what differentiation stage does an erythrocyte discharge its nucleus?

Answer 2

The normoblast stage.

Question 3

What does the early erythroblast do to prepare the cell to become an erythrocyte?

Answer 3

Synthesizes ribosomes

These will later be producing Hb

Question 4

What two stages of erythrocyte differentiation accumulate hemoglobin?

Answer 4

Late erythroblast and normoblast

Question 5

What is the Hb structure for adult Hb?

Answer 5

2x Alpha-globin 2x beta-globin

Question 6

Is heme hydrophobic or hydrophilic?

Answer 6

Hydrophobic

(it hides, nestled inside the globin protiens)

Question 7

What three types of Hb are only found in embryos?

What globin units are unique to these Hb’s?

Answer 7

1. Hb Gower 1
2. Hb Gower 2
3. Hb Portland

zeta and epsilon

Question 8

What is the globin configuration for HbF (fetal)?

Answer 8

2x alpha globin, 2x gamma globin

Question 9

As far as globin synthesis embryologically;

Which globin is produced first as epsilon and zeta are being destroyed?

Which globin comes up next, and then falls off after birth?

Which globin comes up after birth to replace it?

Answer 9

Alpha is produced first, and stays high

Gamma is produced next and falls off at birth

Beta production increases after birth, while gamma production falls off.

(These don’t happen immediately, but are the trends)

Question 10

What two chromosomes hold the globin genes?

Answer 10

Chromosome 16 and 11

Question 11

What current research is underway to possibly treat sickle cell anemia?

What compound are they trying to use to accomplish this?

Answer 11

Trying to induce HbF (using the patient’s wild type gamma-globin to replace their mutant beta-globin)

Hydroxyurea

Question 12

Which histidine is the F8 histidine in hemoglobin?

What does it do?

Answer 12

The proximal histidine.

It is bound to the heme group

Question 13

Which hemoglobin subunit is the distal histidine attached to?

What does it do?

Answer 13

The E7 histidine

Stabalizes oxygen

Question 14

What sort of curve does oxygen binding to myoglobin display?

Answer 14

Hyperbolic curve

Question 15

What sort of curve does oxygen binding to hemoglobin display?

Why does it display this curve?

Answer 15

Sigmoidal (allosteric) binding curve

Because there is cooperativity between O₂ diatoms. One binding makes it easier for another to bind.

Question 16

What is the name for the effect of pH on oxygen binding to hemoglobin?

Answer 16

Bohr’s Effect

Question 17

Besides availability of oxygen, what important factor changes in the peripheral tissues to assist in the release of O₂?

Answer 17

pH!

Peripheral tissue is more acidid, and the H⁺ causes the distal histidine to release the oxygen.

Question 18

What does 2,3-BPG do to the oxygen binding curve?

What is it doing?

Answer 18

Shifts it to the right.

Decreasing the affinity of hemoglobin for oxygen.

Question 19

Why might hemoglobin be more effective at releasing oxygen into exercising tissues?

Answer 19

Because the pO₂ is lower there, so O₂ can more freely dissociate.

Question 20

What is different about the binding affinity of fetal hemoglobin to adult hemoglobin?

What accounts for this difference?

Answer 20

Fetal hemoglobin must have a higher binding affinity for O₂ than the mother’s Hb.

Fetal hemoglobin does not bind well to 2,3-BPG

Question 21

What two protiens store iron?

Answer 21

Ferritin and hemosiderin

Hemosiderin is just degraded ferritin

Question 22

Where do you find the majority of iron in the body?

Answer 22

As Hemoglobin

Question 23

When we eat plants, what form is the iron in?

What form does it need to be in to enter the enterocyte?

What transport protien allows it to enter?

What changes it from one form to the other?

Answer 23

Plant iron is as Fe³⁺

We only absorb Fe²⁺

Divalent Transporter 1

Ferric Reductase changes between the two.

Question 24

What form does iron need to be in to be stored in ferritin?

Answer 24

Fe³⁺

Question 25

What enzyme transports iron out of the enterocyte?

What form must the iron be in to be transported by this protien?

Answer 25

Ferroportin

Fe²⁺

Question 26

What form must iron be in to be transported in the blood?

What protien assists with blood transport of iron?

Answer 26

Fe³⁺

Transferrin

Question 27

What enzyme changes Fe²⁺ into Fe³⁺ in the blood, to be transported by transferrin?

Answer 27

Ferroxidase: Ceruloplasmin / Hephaestin

• Ferroxidase is a familiy of enzymes. Ceruloplasmin is a member of that family, and so is Hephaestin.*
• Hephaestin is named for Hephaestus, Greek god of iron working*
• # Darrenfacts*

Question 28

How does transferin enter a cell?

What special can happen to bring iron directly to mitochondria, where heme is made?

Answer 28

Receptor mediated endocytosis (Transferrin receptors create clatherin coated endosomes)

The endosome can dock directly to the mitochondria, releasing transferring right there - ready to go.

Question 29

How much iron is qualified as hereditary hemochromatosis?

Answer 29

Greater than 15 grams

Question 30

What is the main function of the hormone Hepcidin?

Answer 30

Degradation of ferroportin by tagging it for internalization and proteolysis. (Stops iron from leaving the enterocyte)

Question 31

What does HFE do?

What does its deficiency cause?

Answer 31

Continues the signal of Hepcidin by binding to Tfr2.

Mutation in HFE can cause Hemochromatosis.

• HFE’s real name is “Human Hemochromatosis Protien.” The astute among you may notice that those letters don’t line up. The reason for that is that HFE actually STANDS FOR High Fe, because that’s when it’s active.*
• # Darrenfacts*

Question 32

What sort of anemia might B12 and Folate deficiency cause?

What is this disease due to?

Answer 32

Megaloblastic macrocytic anemia with normal hemoglobin content

Diminished DNA synthesis

Question 33

What other finding (not related to red blood cells) might you find in Megaloblastic macrocytic anemia?

Answer 33

Hyper-segmented neutrophils (more than 5 lobes)

Question 34

What is the active form of folate, and what does it do?

Answer 34

Tetrahydrofolate (THF)

Serves a vital role in DNA synthesis.

(Transfers single carbons)

Question 35

What enzyme converts folate to dihydrofolate, and dihydrofolate to trihydrofolate?

Answer 35

Dihydrofolate reductase (does both reactions using NADPH)

Question 36

Once we get to tetrahydrofolate, what two important paths can it go down?

What do each of those paths do?

Answer 36

1. It can become 5,10 Methylene THF

This accepts a carbon from serine but can get stuck. :(

• MethylENE takes from serINE or makes dTMP but if not for cobalaMINE (sp) it’ll never be SEEN again.*
  2. It can become 5,10 Methenyl THF

This participates in nucleotide synthesis

Question 37

In what form is folate absorbed in the intestine?

Why is this important to know?

Answer 37

N⁵-methyl-THF

Cobalamin is needed just to transform dietary folate!

Question 38

What specific action does cobalamin perform in regards to folate?

Answer 38

It demethylates it!

Question 39

In what foods can you find cobalamin?

What produces cobalamin?

Answer 39

Animal foods only (almost 100% sure this isn’t true, but it’s on the slide - so…)

Microorganisms

Question 40

What is necessary for cobalamin absorption?

What cell produces that?

Where in the gut is it absorbed?

Answer 40

Intrinsic factor

Parietal cells

The Ilium

Question 41

What is the name for B12 related anemia?

Answer 41

Pernicious Anemia

Question 42

What test is used to determine the etiology of B12 deficiency?

Answer 42

Schilling test

Question 43

If your schilling test shows radioactive B12 in the urine before you add intrinsic factor, what is the result?

Answer 43

The patient is absorbing B12 normally, and they have a B12 deficient diet.

Question 44

If you give someone a load of B12, along with a little bit of labeled B12, and you don’t see it in their urine, what are the two possibilities for that patient?

What should you test next?

What are the possible results for that test?

Answer 44

Either they are not absorbing B12 properly, or they are not producing Intrinsic Factor.

Do the same test, but give the patient Intrinsic factor as well.

If the addition of Intrinsic Factor shows B12 in their urine, then it’s an Intrinsic Factor deficiency. Otherwise, they just can’t absorb B12.

Question 45

what role does intrinsic factor play in B12 absorption?

Answer 45

made in stomach and carries b12 to ileum from stomach

intrinsic factor-cobalamin complex is carried by transcobalamin II in blood

this complex is taken up by cells via receptor mediated endocytosis

85% of b12 deficiency is from lack of intrinsic factor

Question 46

What is the folate trap?

Answer 46

If B12 is not available then folate is stuck as N methyl THF

Question 47

What parts of the folate metabolism are key to remember according to Dr. Z?

Answer 47

THF becomes DHF and requires DHF reductase to regenerate the THF form

Later on, N methyl THF needs B12 to become THF

Methotrexate is a stong inhibitor of DHF reductase, decreasing DNA synthesis (TMP-one carbon donation)

Question 48

THF is active form of folate which is important for what?

Answer 48

purine synthesis and thymine synthesis

vital for DNA synthesis

Question 49

Fetal Hgb has what form

Adult Hgb has what two forms?

Answer 49

A2Y2

A2B2

A2D2