Lecture 6: Erythrocyte Biochemistry

Question 1

How does the structure of hemoglobin differ between adult and fetal forms?

Answer 1

Adult: 2 alpha and 2 beta globin chains
Fetal: 2 alpha and 2 gamma globin chains

Question 2

What state is the iron atom in a heme?

Answer 2

Fe 2+ (ferrous)

Question 3

When oxygen binds to a heme group, what happens to iron ion?

Answer 3

Iron movies into plane of heme and pulls down the proximal histidine of hemoglobin
-oxygen forms a hydrogen bond with histidine

Question 4

What type of oxygen saturation curve is seen with a myoglobin?

Answer 4

Hyperbolic curve

-only 1 peptide

Question 5

What type of oxygen saturation curve is seen with a hemoglobin?

Answer 5

Sigmoidal curve

-due to interaction between four globin subunits

Question 6

Describe positive cooperativity.

Answer 6

The binding of one oxygen molecule to hemoglobin makes it easier to bind to other oxygen molecules
-change in one globulin subunit induces a change in another subunit

Question 7

What is the Bohr Effect?

Answer 7

Decreased affinity of hemoglobin for oxygen

-releases oxygen (want this in tissues)

Question 8

What changes are seen in Bohr Effect?

Answer 8

1) Decrease in pH (increase in H+)
2) Increase in 2,3-BPG (tells Hb to give up oxygen)
3) Exercise (drop in partial pressure of oxygen)

Question 9

Why is affinity for oxygen higher in fetal red cells compared to maternal red cells?

Answer 9

Fetus needs to get oxygen from mother

• fetal Hb does not bind well to 2,3-BPG
• left shift

Question 10

In sickle cell disease, where is the mutation?

Answer 10

Amino Acid position #6 in beta globulin

• glutamic acid changes to valine
• polymerization of hemoglobin

Question 11

Where is iron stored?

Answer 11

• Cells that line intestine
• Liver
• Spleen
• Bone Marrow

Question 12

How is heme iron stored?

Answer 12

1) Fe 2+ (heme) enters enterocyte (intestinal cell) and converted into Fe 3+ via ferroxidase
2) Stored as ferritin and can be degraded into hemosiderin

Question 13

How is non-heme iron stored?

Answer 13

1) Fe 3+ is converted into Fe 2+ in the intestinal lumen via ferric reductase in presence of Vit C
2) Fe 2+ enters enterocyte via DMT1
3) Fe 2+ is converted into Fe 3+ via ferroxidase
4) Stored as ferritin and can be degraded into hemosiderin

Question 14

How does iron leave the enterocyte?

Answer 14

1) Must be in Fe 2+ state
2) Leaves basolateral side via ferroportin.
3) Converted to Fe 3+ via ferroxidase
4) Transferrin transports Fe 3+ to liver, spleen, bone marrow

Question 15

Ferroportin requires what for its function?

Answer 15

Hephaestin

Question 16

Ferroportin levels and iron content in the body are regulated by?

Answer 16

Hepcidin

Question 17

Describe the process of transferrin uptake.

Answer 17

1) Uptake via receptor-mediated endocytosis via transferrin receptor
2) Internalized via clathrin pits
3) Transferrin is released in endosome due to low pH
4) Iron is uptaken in mitochondria via DMT1

Question 18

What happens when hepcidin binds to ferroportin?

Answer 18

Internalization of ferroportin and subsequent degradation in lysosomes

Question 19

What regulates levels of hepcidin?

Answer 19

Transferrin and its receptor: Human homeostatic iron regulator protein (HFE)

• High levels of iron (transferrin)n–> hepcidin expression up –> low levels of ferroportin –> low iron absorption levels
• Low levels of iron (transferrin) –> hepcidin expression down –> high levels of ferroportin –> high iron absorption levels

Question 20

What can cause iron deficiency?

Answer 20

• Insufficient dietary iron
• Insufficient absorption
• Excessive blood loss via menstruation
• Overuse of aspirin
• Ulcers of GI tract

Question 21

What can iron deficiency cause?

Answer 21

Hypochromic microcytic anemia

Question 22

What can iron overload cause?

Answer 22

Hereditary Hemochromatosis

• accumulation of iron in heart, liver, and pancreas, which can cause severe issues
• autosomal recessive in HFE gene
• 15 g of iron instead of normal 3-5

Question 23

RBC production is dependent on what?

Answer 23

Folate
Vitamin B12 (cobalamin)

Question 24

What can a deficiency in folate and vitamin B12 cause?

Answer 24

Megaloblastic anemia

• diminished synthesis of DNA
• large RBC

Question 25

What is the active form of folate?

Answer 25

Tetrahydrofolate (THF)

Question 26

What is the role of THF?

Answer 26

Synthesis of purines and thymine

Question 27

Where is folic acid absorbed?

Answer 27

Small intestine (jejunum)

Question 28

Where is folic stored?

Answer 28

Liver

Question 29

In dietary sources, folate is in what form?

Answer 29

DHF

Question 30

In the intestines, folate acid is reduced to what form?

Answer 30

N5-methyl-THF

Question 31

What enzyme converts FH2 (DHF) into FH4 (THF)

Answer 31

Dihydrofolate Reductase

Question 32

What inhibits dihydrofolate reductase?

Answer 32

Methotrexate

Question 33

What is an important component of Vit B12?

Answer 33

Cobalt

Question 34

What does Vit B12 do?

Answer 34

Removes methyl group from N5-methyl-THF to generate FH4 (THF)

Question 35

Where is Vit B12 found?

Answer 35

Animal products

-made by microorganisms

Question 36

What is the main cause of Vit B12 deficiency?

Answer 36

Lack of protein: intrinsic factor

Question 37

How is Vit B12 absorbed?

Answer 37

1. Dietary Vit B12 binds to R-binder proteins
2. Intrinsic factor carries B12 to ileum and it is released into blood stream from there by transcobalamin II
3. Intrinsic Factor-cobalamin complex taken up by cells via receptor-mediated endocytosis

Question 38

What is pernicious anemia?

Answer 38

Megaloblastic macrocytic anemia

-Vit B12 deficiency due to lack of intrinsic factor

Question 39

How do you test for pernicious anemia?

Answer 39

1) Oral dose radioactive Vit B12
- if it is seen in urine 24 hours later, then it has been absorbed

2) If radioactive Vit B12 not seen in urine, oral dose of radioactive Vit B12 + Intrinsic factor
- if it is seen in urine 24 hours later, then pernicious anemia is due to lack of intrinsic factor