The synthesis of the globin chains- a , b , d , e ,
g , and z , is controlled by structural genes on chromosomes
16 ( a ; z ) and 11 ( b , d , e , g ). The location and
rate of synthesis varies from embryonic to fetal to neonatal
to adult life.
Four polypeptide globin chains are arranged in pairs
forming the tetrameric molecule or globin portion of hemoglobin.
Each globin chain is covalently attached to a heme moiety.
The globin tetramer is globular or ellipsoid in shape,
being approximately 550nm in diameter. The four porphyrin
heme moieties lie in four regularly spaced clefts on the
The globin portion of most normal hemoglobins consists
of two chains from chromosome 16 and two from chromosome
Normal a chains contain 141 amino acids; normal ß
chains 146 amino acids. The d chain varies by 10 aa; the
g chain by 39 aa compared with the ß chain.
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