SYNTHESIS OF HEMOGLOBIN
Synthesis of hemoglobin actually
starts in proerythroblastic stage. However, hemoglobin appears
in the intermediate normoblastic stage
only. Production of hemoglobin is continued until the stage of reticulocyte. Heme
portion of hemoglobin is synthesized in mitochondria. And the protein part, globin
is synthesized in ribosomes.
SYNTHESIS OF HEME
Heme is synthesized from succinylCoA and
the glycine.
The sequence of events in synthesis of
hemoglobin:
1. First step in heme synthesis takes
place in the mitochondrion.
Two molecules of succinylCoA combine with
two molecules of glycine and condense to form
δ-aminolevulinic acid
(ALA) by ALA synthase.
2. ALA is transported to the
cytoplasm. Two molecules of ALA combine to form porphobilinogen in the
presence of ALA dehydratase.
3. Porphobilinogen is converted into
uroporphobilinogen I by uroporphobilinogen I synthase.
4. Uroporphobilinogen I is converted
into uropor phobilinogen III by porphobilinogen III cosynthase.
5. From uroporphobilinogen III, a ring
structure called coproporphyrinogen III is formed by
uroporphobilinogen decarboxylase.
6. Coproporphyrinogen III is
transported back to the mitochondrion, where it is oxidized to form
protoporphyrinogen IX by coproporphyrinogen oxidase
7. Protoporphyrinogen IX is converted
into protoporphyrin IX by protoporphyrinogen oxidase.
8. Protoporphyrin IX combines with
iron to form heme in the presence of ferrochelatase.
FORMATION OF GLOBIN
Polypeptide chains of globin are
produced in the ribosomes. There are four types of polypeptide chains
namely, alpha, beta, gamma and delta
chains. Each of these chains differs from others by the amino acid
sequence. Each globin molecule is
formed by the combination of 2 pairs of chains and each chain is made of 141 to
146 amino acids. Adult hemoglobin contains two alpha chains and two beta
chains. Fetal hemoglobin contains two alpha chains and two gamma chains.
CONFIGURATION
Each polypeptide chain combines with
one heme molecule. Thus, after the complete configuration, each
hemoglobin molecule contains 4
polypeptide chains and 4 heme molecules.
SUBSTANCES NECESSARY
FOR HEMOGLOBIN SYNTHESIS
Various materials are essential for the
formation of hemoglobin in the RBC..
hemoglobin molecule contains 4
polypeptide chains and 4 heme molecules.
SUBSTANCES NECESSARY
FOR HEMOGLOBIN SYNTHESIS
Various materials are essential for
the formation of hemoglobin in the RBC .
DESTRUCTION OF HEMOGLOBIN
After the lifespan of 120 days, the
RBC is destroyed in the reticuloendothelial system, particularly in spleen and
the hemoglobin is released into plasma. Soon, the hemoglobin is degraded in the
reticuloendothelial cells and split into globin and heme. Globin is utilized
for the resynthesis of hemoglobin. Heme is degraded into iron and porphyrin.
Iron is stored in the body as ferritin and hemosiderin, which are reutilized
for the synthesis of new hemoglobin. Porphyrin is converted into a green
pigment called biliverdin. In human being, most of the biliverdin is converted
into a yellow pigment called bilirubin. Bilirubin and biliverdin are together
called the bile pigments
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