STRUCTURE OF HEMOGLOBIN , FUNCTION

-- Hemoglobin is spherical or globular in shape

-- It is  present inside RBC

-- It is a conjugated tetrameric protein made of 

   Protein component - Globin chain &

   Prosthetic or non protein component -  Heme

-- Molecular weight of hemoglobin is 67000 Daltons.

STRUCTURE OF HEME 

-- Heme is the non-protein part of hemoglobin

--It is a derivative of porphyrin.

-- Porphyrin is a cyclic compound formed by the fusion of four pyrrole rings and so it is a tetrapyrrole structure

-- The pyrrole rings are joined together by methenyl (=CH-) bridges

-- Iron is present in the center of proto- porphyrin molecule and it is held by forming coordinated bonds with four Nitrogen's (N) of the four porphyrin rings.

--  Heme is also called as ferroprotoporphyrin as iron is present in the center of the porphyrin ring.

-- The four pyrrole rings present in heme are numbered as I,II,III,IV and the methenyl bridges are named as alpha, beta, gamma & delta

STRUCTURE OF GLOBIN

-- It is the protein part of hemoglobin

-- It consists of four polypeptide chains which are arranged in pairs.

-- The different type of polypeptide globin chains synthesized during the course of life time are alpha (α), beta(β), gamma( γ), delta(δ) and epsilon(ε)

Different types of hemoglobin present during the course of life time

1. Embryonic Hb  -   HbE -       γ₂δ₂

2. Fetal Hb -               HbF -       α₂γ₂

3. Adult Hb Type 1    HbA1-      α₂β₂

4. Adult Hb Type 2    HbA2-      α₂δ₂

  ATTACHMENT OF GLOBIN TO HEME

-- Each peptide chain of the globin molecule is covalently attached to iron of the Heme molecule.

-- The N atoms of the proximal and distal histidine residue gets covalently linked with the Fe2+ of iron

-- Iron of heme molecule carries oxygen 

-- In oxygenated Hb - Oxygen is present in between the Fe2+ and distal histidine

-- In deoxygenated Hb - water molecule is present in between iron and distal hsitidine

One Hemoglobin molecule has four globin chains that are linked to four heme molecules 

Thus, one molecule of Hemoglobin can carry four molecules of Oxygen

 Normal adult circulation comprises of  95%HbA1 + 4.5%HbA2 + 0.5%HbF

FUNCTIONS OF HEMOGLOBIN

1. Transport of O2 from lungs to tissues
2. Transport of CO2 and H+ from tissues to lungs and kidney 
3. Acts as an intracellular buffer and is thus involved in acid-base balance.