Erythrocyte Biochemistry

Question 1

Overall Hb structure

Answer 1

Tetramer with 2 a-chains and 2 b-chains. Contains Fe2+ subunit. Hydrophobic.

Question 2

HbS and HbF

Answer 2

Research ongoing to induce expression of HbF via hydroxyurea to address inflammation. However, HbF is a toxic chemotherapeutic agent.

Question 3

Proximal and distal Histidines

Answer 3

Proximal: F8. Bound to heme.

Distal Histidine: E7. O2 binds to the iron between the heme and distal His.

Question 4

Oxygen dissociation curves

Answer 4

Mb: hyperbolic.
Hb: sigmoidal (due to interactions between globin subunits).
Hb has 2 affinity states. Binding of O2 is reversible.

Question 5

Positive cooperative binding

Answer 5

Hb binding O2 facilitates binding of another O2. A conformational change allows accommodation for another O2.

Question 6

The Bohr Effect

Answer 6

Binding affinity of Hb for O2 decreases as pH decreases.

His picks up H+ from tissue causing release of O2.

Question 7

Modulation by 2,3-BPG

Answer 7

Reduces O2 affinity so Hb gives up more O2 to tissues. Signals to Hb to let O2 go. Shifts ODC right.

Question 8

ODC in HbF

Answer 8

HbF does not bind 2,3-BPG well, increasing its affinity. Shifts curve to the left. O2 flows from mother to fetus.

Question 9

Storage Iron

Answer 9

Ferratin: water soluble.
Hemosiderin: water insoluble.

Question 10

Absorption of Iron

Answer 10

Fe cannot freely diffuse across membrane; involves 5 proteins.

Question 11

Proteins involved in uptake of Fe (5)

Answer 11

Ferric reductase
DMT1
Ferroportin
Hephaestin
Transferrin

Question 12

Ferric reductase

Answer 12

Converts Fe3+ (in non-heme iron) to Fe2+.

Question 13

DMT1 (divalent transporter-1)

Answer 13

Takes up Fe2+

Question 14

Ferroportin

Answer 14

Forces iron out of cell.

Question 15

Hephaestin

Answer 15

Converts free iron to Fe3+.

Question 16

Transferrin

Answer 16

Transports iron in blood.

Question 17

Fe2+ and Fe3+

Answer 17

Dietary iron is Fe3+, but needs to be Fe2+ to enter the cell. Once Fe2+ leaves the cell, it is converted to Fe3+ so it can be carried to the bone marrow.

Question 18

Transferrin receptor (TfR) mediated endocytosis

Answer 18

Clathrin coated pits take in iron, and transport to the mito via endosome.. DMT1 transports iron out of endosome.

Question 19

Hereditary hemochromatosis

Answer 19

Organ dysfunction due to iron overload. Caused by poor regulation of iron uptake and export by enterocyte.

Question 20

Hepcidin

Answer 20

Regulated uron homeostasis.

Binds ferroportin, causing it to become internalized where it is destroyed.

Question 21

When iron level is high:

Answer 21

Hepcidin expression is up, ferroportin levels are down, iron absorption is low.

Question 22

When iron level is low:

Answer 22

Hepcidin expression is down, ferroportin levels up, iron absorption is high.

Question 23

Regulation of hepcidin expression

Answer 23

If Hfe is mutated, it cannot bind TfR2.

Therefore, it cannot turn on hepcidin expression, so there is no control over ferroportin activity.

Question 24

RBC production dependent on (2)

Answer 24

Vit B12

Folate

Question 25

Megaloblastic anemia

Answer 25

Anemia due to Vit B12 and folate deficiency.

Characterized by large RBCs. Have normal Hb content in relation to size.

Question 26

Structure of folate (3 parts)

Answer 26

1. Pteridine: N containing ring.
2. PABA
3. Glu residue chains.

Question 27

Pernicious anemia

Answer 27

Type of megaloblastic anemia from vit B12 deficiency due to lack of intrinsic factor.
Occurs in the elderly and may involve an autoimmune disease.

Question 28

Folate metabolism

Answer 28

Folate —> FH2 —> THF (both via dihydrofolate reductase).
THF can become methylene, methynyl or formyl.
Methylene can become methyl which require B12 to become THF again. Formyl goes to de novo synthesis of pyrimidines.

Question 29

Vitamin B12 absorption

Answer 29

B12 + R-binder (from gastric mucosa cells) combine.
Proteases cleave to free B12.
Intrinsic factor (from parietal cells) bind B12 and bring to ileum.

Question 30

Schilling Test part I

Answer 30

Pt given labeled Co and trace unlabeled Co.
Urine collected after 24 hrs.
If there is not radioactive Co, then B12 is not absorbed (continue to part II).
If there is radioactive Co, then there must be a dietary deficiency.

Question 31

Schilling Test part II

Answer 31

Give radioactive Co and intrinsic factor.
Evaluate urine after 24 hrs.
If Co is absent in urine, it is due to lack of intrinsic factor and pt has pernicious anemia.

Question 32

Components of embryonic, fetal and adult Hb and production graph.

Answer 32

Embryonic: Gower I, Gower II, Portland.
Fetal: a-2, y-2.
Adult: a-2, b-2.
can have a-2, d-2.
Draw graph.