Structure and function of hemoglobin

Question 1

What are the main components of HbA?

Answer 1

2-alpha chains
2-beta chains
Heme

Question 2

What are the main components of HbA2

Answer 2

2-alpha chains
2-sigma chains
Heme

Question 3

What are the main components of HbF?

Answer 3

2 alpha chains
2 gamma chains
Heme

Question 4

What are the main components of HbA1c?

Answer 4

2 alpha chains
2 beta chains
Glucose

Question 5

What is the attachment point of the glucose on HbA1c?

Answer 5

Amino group of the N-terminal valine of the beta-globin chain

Question 6

What chromosome carries the alpha-globin genes?

Answer 6

Chromosome 16

Question 7

What chromosome carries the beta-globin genes?

Answer 7

Chromosome 11

Question 8

What are the embryonic hemoglobins?

Answer 8

Hb Gower 1
Hb Gower 2
Hb Portland

Question 9

What, located upstream of the beta-globin genes, plays a significant role in expression?

Answer 9

Locus control region

Question 10

What are the components of heme?

Answer 10

Ferrous iron - Fe++
Protoporphyrin IX

Question 11

What are the 6 bonds to the ferrous iron in heme?

Answer 11

4 to the nitrogens in the porphyrin ring
1 to the histidine of globin
1 left available to bind to O2

Question 12

How many heme are in each hemoglobin?

Answer 12

4

Question 13

What is the function of the distal histidine in the heme binding site?

Answer 13

Stabilizes O2 binding to Fe++

Question 14

What is the T form of Hgb?

Answer 14

Deoxygenated form with a low affinity for oxygen

Question 15

What is the R form of Hgb?

Answer 15

Oxygenated form with high O2 affinity

Question 16

What is the purpose of cooperative binding?

Answer 16

Allows Hgb to deliver more O2 to tissues

Question 17

What is the function of myoglobin?

Answer 17

Reservoir of oxygen and as an oxygen carrier in muscle cells

Question 18

What is the shape of the oxygen dissociation curve for myoglobin?

Answer 18

Hyperbolic

Question 19

What is the shape of the oxygen dissociation curve for hemoglobin and why?

Answer 19

Sigmoidal because of cooperative binding

Question 20

What factors affect the unloading and loading of O2 to hemoglobin?

Answer 20

PO2
pH
PCO2
Concentration of 2,3-BPG

Question 21

What is the influence of low pH and increased PCO2 on the oxygen dissociation curve?

Answer 21

Increased unloading, shift curve to the right

Question 22

What will happen to the oxygen dissociation curve if Hgb has a higher affinity for oxygen?

Answer 22

It shifts to the left

Question 23

What is the function of 2,3-BPG and when is its concentration higher?

Answer 23

Decreases oxygens affinity for Hgb

Hypoxia and anemia

Question 24

What occurs to the oxygen dissociation curve in chronic anemia?

Answer 24

Curve shifts to right –> increased O2 disassociation

Question 25

What occurs to the oxygen dissociation curve during a panic attack?

Answer 25

Curve shift to the left --> hypoventilation decreased PCO2

Question 26

What occurs to the oxygen dissociation curve in hypothermia?

Answer 26

Shifts to the left

Question 27

What component performs the buffering action of Hb?

Answer 27

Imidazole group of histidine residues binds H+

Question 28

What is the defect in HbS?

Answer 28

Glutamic acid at 6th position of beta-globin chain is replaced by valine

Question 29

What is the defect in HbC?

Answer 29

Glutamic acid in the 6th position of beta-globin is replaced by lysine

Question 30

What is the defect in HbSC?

Answer 30

Both HbS and HbC present

Question 31

What is defect in thalessemia?

Answer 31

Imbalance in the synthesis of globin chains

Question 32

What is the defect in methemoglobinemias/HbM)

Answer 32

Oxidation of heme iron from ferrous to ferric (Fe++ to Fe+++)

Question 33

Is HbM/metHb able to bind oxygen?

Answer 33

No

Question 34

What characterizes HbM?

Answer 34

Chocolate cyanosis --> brown colored blood with cyanosis

Question 35

What enzyme may be deficient in HbM?

Answer 35

NADH-metHb reductase

Question 36

What is the treatment for metHb?

Answer 36

Methylene blue

Question 37

What can cause acquired metHb?

Answer 37

nitrate drugs

Question 38

What changes to the oxygen dissociation curve are seen with CO?

Answer 38

Shifts curve to the left Lowers plateau Becomes hyperbolic