Structure and Functions of Haemoglobin (or)
Oxygen transport and storage: Structure of Haemoglobin, Binding and transport of
oxygen
→ Structure of Haemoglobin (Hb or Hgb):-
Haemoglobin is a red pigment of blood. Each hemoglobin molecule is made up of 4 heme groups surrounding a
globin group, forming a tetrahedral structure. It is 64 Å in length.
In Haemoglobin, the protein part is globin (94%). Globin consists of two linked pairs of polypeptide chains.
Each peptide chain contains 146 amino acid units.
Heme accounts for only 4% of the weight of the molecule and is composed of a ring-like organic compound
known as a “porphyrin” to which an iron atom is attached. The heme is strongly covalently bond to the globular
protein by the N-atoms of histidine group till 5th position. The 6th position of heme is bond with oxygen of
oxyhaemoglobin by a coordinate covalent bond, completing the octahedral group.
→ Functions of Haemoglobin :-
a) Binding and Transport of oxygen: Haemoglobin acts as a carrier of oxygen from lungs to tissues. In
haemoglobin, the co-ordination number of iron is 6 and it reversibly combines with oxygen to form an
unstable complex called oxyhemoglobin. Each iron in the heme group can bind 1 molecule of oxygen.
Since each hemoglobin molecule contains 4 heme groups, each hemoglobin molecule is able to bind
with 4 molecules of oxygen.
Hb + 4O2 ⇌ Hb (O2)4
(Haemoglobin) (Oxyhaemoglobin)
This combination changes hemoglobin's shape and turns it to a ruby red color. The oxyhemoglobin
travels to the body tissues, where it releases some of its oxygen molecules depending on the need for
metabolic activity. From tissues, oxygen is transferred to myoglobin for respiration.
b) Transport of CO2: Hemoglobin is a two-way respiratory carrier, transporting oxygen from the lungs to
the tissues and facilitating the return transport of carbon dioxide.
Carbon dioxide enters the bloodstream via capillaries and is then carried to lungs to be exhaled.
Approximately 75% CO2 dissolves in the plasma and remaining 20-25% of CO2 binds to the amino acids
in hemoglobin forming carbaminohemoglobin complex.
c) Combination with CO: Carbon monoxide is highly poisonous. It can bind to haemoglobin and form a
highly stable complex called carboxyhaemoglobin. Haemoglobin has 250 times higher affinity for CO
than O2. Inhaling air rich in CO can affect the binding of oxygen. It can block 20% of active binding
By: ZOHA KARIM pg. 1
Oxygen transport and storage: Structure of Haemoglobin, Binding and transport of
oxygen
→ Structure of Haemoglobin (Hb or Hgb):-
Haemoglobin is a red pigment of blood. Each hemoglobin molecule is made up of 4 heme groups surrounding a
globin group, forming a tetrahedral structure. It is 64 Å in length.
In Haemoglobin, the protein part is globin (94%). Globin consists of two linked pairs of polypeptide chains.
Each peptide chain contains 146 amino acid units.
Heme accounts for only 4% of the weight of the molecule and is composed of a ring-like organic compound
known as a “porphyrin” to which an iron atom is attached. The heme is strongly covalently bond to the globular
protein by the N-atoms of histidine group till 5th position. The 6th position of heme is bond with oxygen of
oxyhaemoglobin by a coordinate covalent bond, completing the octahedral group.
→ Functions of Haemoglobin :-
a) Binding and Transport of oxygen: Haemoglobin acts as a carrier of oxygen from lungs to tissues. In
haemoglobin, the co-ordination number of iron is 6 and it reversibly combines with oxygen to form an
unstable complex called oxyhemoglobin. Each iron in the heme group can bind 1 molecule of oxygen.
Since each hemoglobin molecule contains 4 heme groups, each hemoglobin molecule is able to bind
with 4 molecules of oxygen.
Hb + 4O2 ⇌ Hb (O2)4
(Haemoglobin) (Oxyhaemoglobin)
This combination changes hemoglobin's shape and turns it to a ruby red color. The oxyhemoglobin
travels to the body tissues, where it releases some of its oxygen molecules depending on the need for
metabolic activity. From tissues, oxygen is transferred to myoglobin for respiration.
b) Transport of CO2: Hemoglobin is a two-way respiratory carrier, transporting oxygen from the lungs to
the tissues and facilitating the return transport of carbon dioxide.
Carbon dioxide enters the bloodstream via capillaries and is then carried to lungs to be exhaled.
Approximately 75% CO2 dissolves in the plasma and remaining 20-25% of CO2 binds to the amino acids
in hemoglobin forming carbaminohemoglobin complex.
c) Combination with CO: Carbon monoxide is highly poisonous. It can bind to haemoglobin and form a
highly stable complex called carboxyhaemoglobin. Haemoglobin has 250 times higher affinity for CO
than O2. Inhaling air rich in CO can affect the binding of oxygen. It can block 20% of active binding
By: ZOHA KARIM pg. 1
