Hemoglobin

Question 1

What is the function of Hemoglobin?

Answer 1

Hemoglobin is a highly specialized intracellular protein that transports oxygen from lungs to tissue and facilitates CO2 transfer from tissue to lungs

Question 2

How much Hemoglobin is in an RBC?

Answer 2

28-34 pg
Measured as the mean corpuscular hemoglobin (MCH)

Question 3

What is the normal concentration of HB in adult?

Answer 3

15 g/dL

Question 4

Where is hemoglobin made?

Answer 4

In the polychromatophilic normoblast

Question 5

What is the lifespan of an RBC?

Answer 5

120 days

Question 6

Describe the structure of a Hemoglobin?

Answer 6

Four globular protein subunits
Each subunit has a heme group and a globin chain
The structure is held together by salt bonds, hydrophobic contacts and hydrogen bonds. It forms a tetramer with two pairs of unlike chains.
Two identical alpha-like chains
Two identical nonalpha chains

Question 7

What is the Heme composed of?

Answer 7

Heme is a tetrapyrrole ring with a ferrous (Fe2+) iron in the center
Each heme subunit can carry one molecule of oxygen bound to the central ferrous iron
Each hemoglobin molecule can carry four molecules of oxygen

Question 8

Describe the globin chains found in a hemoglobin structure

Answer 8

There are two types of chain.
Alpha like: Alpha, zeta
Nonalpha: epislon, beta, delta, gamma

Question 9

Describe the Primary Struture of Hemoglobin

Answer 9

Sequence of individual amino acids held together by peptide bonds in the globin chains; is critical to stability and function of molecule; determines the overall structure

Question 10

Describe the Secondary structure of Hemoglobin

Answer 10

Arrangement of the amino acids resulting from hydrogen bonding between the peptide bonds of the amino acids next to or near each other

Question 11

Describe the Tertiary structure of Hemoglobin

Answer 11

Folding superimposed on the helical and pleated domains; forms the heme hydrophobic pocket within globin chains and places polar (hydrophilic) residues on the exterior of the molecule; this tertiary structure changes upon ligand binding

Question 12

Describe the Quarternary structure of a hemoglobin

Answer 12

Relationship of the four protein subunits to one another; quaternary structural changes that occur upon ligand binding result from the tertiary changes

Question 13

Describe the structure of heme

Answer 13

A porphyrin ring with a ferrous iron in the center

Question 14

Where does heme synthesis takes place?

Answer 14

Starts in the mitochondria, then moves to the cytoplasm and then back to the mitochondria

Question 15

What steps of heme synthesis occurs in the mitochondria?

Answer 15

The condensation of glycine and succinyl CoA forms 5-aminolevulinic acid (ALA). Requires cofactor pyridoxal phosphate, succinyl CoA synthase and 5-aminolevulinate synthase (ALAS)
This is a rate limiting step

5-Aminolevulinate synthase leaves the mitochondria to the cytoplasm

Coproporphyrinogen reenters the mitochondria to form the protoporphyrin IX ring.
Iron enters the ring to form heme.

Question 16

Describe the steps that takes in the cytoplasm of heme synthesis

Answer 16

1. ALA (5-aminolevulinate) enters the cytoplasm and is converted to porphobilinogen (PBG) by ALA dehydrase
2. Porphobilinogen (PGB) is converted to Hydroxymethylbilane by porphobilinogen deaminase
3. Hydroxymethybilane is converted Uroporphobilinogen III
4. Uroporphobilinogen is converted to Coproporphyrinogen III
5. Coproporphyrinogen III moves back to the mitochondria to become protophorphyrinogen and then combine with iron to become heme.

Question 17

What globin chain are found only in embryonic HbS?

Answer 17

Zeta and Epsilon

Question 17

Which chromosome codes for zeta and alpha?

Answer 17

Chromosome 16

Question 18

Which globin chain replaced zeta during 8-12 weeks of embryonic development?

Answer 18

Zeta is replaced by Alpha chain synthesis

Question 19

Which type of hemoglobin is dominant in adults?

Answer 19

HbA

Question 19

What globin chain are found in HbA?

Answer 19

Alpha and Beta

Question 20

What hemoglobin chains are found in fetal hemoglobin?

Answer 20

Alpha and Gamma

Question 21

Where does globin synthesis takes place?

Answer 21

On polyribosomes in the cytoplasm of erythroblast

Question 22

What are the embryonic hemoglobin called?

Answer 22

Gower I (Zeta and Epsilon), Gower II (Alpha and Epsilon) and Portland (Zeta and Gamma)