Hemoglobin & Myoglobin

Question 1

Structure of Haem

Answer 1

• Haem is a complex of protoporphyrin IX and ferrous iron (Fe2+)
• Iron is held in the center of the heme molecule by bonds to the four nitrogens of the porphyrin ring.
• Iron can form six coordinate bonds:
  →Four nitrogen of porphyrin ring
  →One bond with proximal histidine (F8) residue of globin
  →Other position is available to bind to oxygen reversibly

Question 2

Structure of Myoglobin

Answer 2

*Primary structure: One polypeptide chain made up of 153 amino acids
*Secondary structure: Polypeptide folded into eight alpha helices labeled A→H. stabilized by hydrogen bonds
Tertiary structure:
* Globular structure.
* Stabilized by hydrophobic interactions.
* Hydrophobic amino acids located in the interior of the protein.
* Haem located in the central crevice lined by non-polar amino acids.
* The proximal histidine binds directly to the iron of haem.
* Distal histidine does not directly interact with the haem group but helps stabilize the binding of oxygen to the ferrous iron.

Question 3

haemoglobin structure

Answer 3

*Structurally and functionally more complex than myoglobin

*Primary: Made up of four polypeptide chains- 2 & 2
chains held together by non-covalent interaction
*-chain:141 amino acids
*-chain: 146 amino acids
* Secondary:
*a chain is made up of 7 a helices
- b chain is made up of 8 a helices

• Tertiary:
• Every hemoglobin chain similar to but not identical to myoglobin chain

Quaternary structure:
* Made up of four polypeptide chains
* Hetero-tetramer :2a chains and 2b chains in which
refer to dimers one and two
* Two identical dimers: (ab)1 and (ab)2 with lot of contact
* Each dimer is stabilized by hydrophobic interactions, ionic and hydrogen bonds
* Weak polar interactions between 2 dimers results in the two dimers occupying different relative positions in deoxyhaemoglobin as compared with oxyhaemoglobin (T and R form)
*Two dimers are able to move with respect to each other

Question 4

Types of Hemoglobin

Answer 4

HbA
❑Is the major hemoglobin and is composed of 2α and 2β chains.

HbA2
Is the minor adult Hb and is composed of 2α and 2δ chains.

HbF
❑is synthesized during fetal development
❑It is only represented as <2% of the hemoglobin in adult blood.
❑HbF is concentrated in RBCs known as F cells.

HbA1C
❑Has glucose residues attached to β-globin chain

table

Question 5

Hemoglobin A1c(HBA1c)

Answer 5

• most abundant form of
  glycosylated hemoglobin
  which has a glucose residues attached
  to b globin- chain in hemoglobin RBC
• increased amounts of HbA 1C IN RBC of diabetes mellitus patients