Lect 10 Erythrocyte Biochemistry

Question 1

What is Erythropoiesis?

What are the stages?

When is majority of Hb synthesized?

Answer 1

RBC production

Hemocytoblast –> Proerythroblast -> Early Erythroblast –> Late Erythroblast –> Normoblast –> Reiculocyte –> Erythrocyte

Prior to extrusion of the nucleus

Question 2

Adult Hb is a multi-subunit protein (tetramer) made up of what subunits?

Characteristics of Heme

Answer 2

• 2 a-globin chains & 2 B-globin chains
• Heme:
  
  • One per subunit
  • Has iron atom (ferrous: Fe²⁺)
  • Carries O₂
  • Hydrophobic

Question 3

Types of Hb

Embyronic composition? When are they gone?

Fetal composition?

Adult composition?

Which chromosomes have genes for subunit production?

Answer 3

• Embryonic:
  
  • Hb Gower 1; Hb Gower 2; Hb Portland
  • Week 8
• Fetal:
  
  • HbF (a₂y₂)
• Adult
  
  • HbA (a₂B₂)
• 16 & 11

Question 4

How is HbF being used in Sickle Cell Anemia (HbS)?

Downsides?

Answer 4

Using hydroxyurea to induce HbF and address inflamation

Toxic chemotherapeutic agent

Question 5

Which is the proximal histidine and what is it bound to?

Which is the distal histidine and what is it bound to?

O₂ binding –> Conformational change –> Changes position of iron in plane of heme, which histidine moves with the iron?

Answer 5

F8 Histidine (Proximal) is bound to Heme

E7 Histidine (Distal) binds to O₂ that is bound to iron in Heme

F8 (Proximal) Histidine is pulled down

Question 6

What type of dissociation curve for myoglobin? Hemoglobin?

What is Cooperativity?

Answer 6

Myoglobin: Hyperbolic

Hemoglobin: Sigmoidal

Binding/Releasing one O₂ to/from heme, facilitates further binding/releasing of O₂

Question 7

O₂ Dissociation Curve (ODC): Bohr Effect (pH)

What is the change in pH from Lungs to actively respiring tissues?

How is binding affinity of Hb affected?

Answer 7

7.4 –> 7.2

Binding affintiy decreases as pH decreases

Question 8

ODC: Modulation by 2,3-BPG

What is the affect on Hb by 2,3-BPG?

Answer 8

Reduces O₂ affinity so gives up more oxygen to tissues

Question 9

ODC: Modulation by Exercise

What is the difference in providing O₂ to resting tissues and exercising tissues?

Answer 9

Drop in pO₂ from 40 (rest) –> 20 (exercise) leads to increased oxygen offloading to tissues

Question 10

ODC: Fetal (HbF) & Maternal (HbA) RBCs

What is the reason O₂ flows from mother to fetus?

Answer 10

HbF has higher affinity for O₂ (does not bind well to 2,3-BPG)

Question 11

Distribution of Iron in Humans

What are the two types of storage iron?

Answer 11

Ferritin (H₂O soluble)

Hemosiderin (H₂O insoluble)

Question 12

Iron Absorption, Storage, and Transport

How is Nonheme iron Fe³⁺ (plant products) and Heme iron Fe²⁺ (animal products) transferred to blood?

What are the storage forms and what type of iron is used?

Answer 12

1. Converted to Fe²⁺ (Ferric Reductase/Dcytb) for Nonheme (Fe³⁺)
2. Into enterocyte (Divalent Transporter 1/DMT1 on Apical)
3. Transport into blood (Ferroportin on Basolateral)
4. Fe²⁺ –> Fe³⁺ in blood (Ferroxidase / Cerruloplasmin / Hephaestin)
5. Transported to tissues via Transferrin

• Fe³⁺ –> Ferritin –> Hemosiderin (Via degradation)

Question 13

Transferrin Receptor (TfR) Mediated Endocytosis

How is Transferrin internalized and where is it taken?

What transports iron out of endosome?

Answer 13

Calthrin coated pits (endosomes) transport iron to mitochondria

DMT1

Question 14

Causes of Iron Deficiency?

Answer 14

• Insufficient dietary iron
• Menstruation
• Aspirin overuse
• GI ulcers –> Blood loss

Question 15

Hereditary Hemochromatosis

What is it?

What is the normal total body iron level and what is level in those with H.H.?

Answer 15

Organ dysfunction due to iron overload

3-5g normal & 15g H.H.

Question 16

Hepcidin

Where does Hepcidin bind and what does it do?

What happens when iron levels are high?

What happens when iron levels are low?

What happens if Hfe is mutated?

Answer 16

Binds to Ferroportin and causes internalization of Ferroportin (Destroyed by proteolysis)

Hepcidin expression increases

Hepcidin expression decreases

Hepcidin expression inhibited, no control of ferroportin activity

Question 17

RBC Production

Dependent on what?

Deficiencies in these can cause what?

Why does this occur?

How are the cells characterized?

Answer 17

• Vit B12 (Cobalamin) & Folate (Folic Acid)
• Megaloblastic Macrocytic Anemia
  
  • Diminished DNA synthesis in developing RBC in BM
  • Large RBCs

Question 18

Structure of Folate (Folic Acid)

What is the active form? What is its role?

Answer 18

• Pteridine (N containing ring); PABA; Glutamate
• THF (Tetrahydrofolate) –> Plays role in DNA synthesis by transfering C units from donors to acceptors

Question 19

Folate Metabolism

Carbon side chain of serine transferred to ​THF to form N-methylene-THF, what can this then give rise to?

What else can it produce and what is required to reverse it?

What is a third potential product and its application?

Answer 19

• Carbon of N-methylene-THF –> dUMP –> dTMP (DNA synthesis) + DHF (dihydrofolate reductase) –> THF
• N-methylene-THF can also be converted to N-methyl-THF (trapped - requires Vit B12/Cobalamin)
• N-methenyl-THF which can be used in de novo purine biosynthesis

Question 20

Folic Acid: Requirements

Initially absorbed as folic acid (DHF), what is it converted to in SI (primary circulating form of THF in blood stream)?

Answer 20

N-methyl-THF

Question 21

B12 Absorption

What does B12 bind to in stomach?

Proteases break down down R-Binder proteins in duodenum, what carries B12 to ileum where it is taken up into the body?

Intrinsic Factor-Cobalamin taken up by what process?

Cobalamin circulates thorugh the blood carried by what?

Answer 21

R-Binder proteins

Intrinsic factor (made by parietal cells in stomach)

Receptor-mediated Endocytosis

Transcobalamain

Question 22

Pernicious Anemia

Vit B12 deficiency can occur due to lack of what?

What type of anemia?

Answer 22

Intrinsic factor

Megaloblastic Macrocytic Anemia