Glutamic acid hemoglobin

Sickle hemoglobin A defective form of hemoglobin produced as a result of a single substitution of the amino acid valine for glutamic acid at position 6 of the (1-polypeptide chain. 

One of the amino acids in the beta polypeptide chain of hemoglobin is glutamic acid (Fig. 7.11.1). 

The hydrophilic polar side group on glutamic acid is capable of forming hydrogen bonds with water and thus helps to keep normal hemoglobin dispersed within the red blood cells. 

In sickle cell hemoglobin, the glutamic acid of the beta subunit is replaced by the amino acid valine (Fig. 7.11.2). Even though only this one amino acid is... 

Sickle cell anemia is caused by synthesis of a mutant form of hemoglobin, hemoglobin 5 or HbS), in which a glutamic acid at position 6 of the hemoglobin (3 subunit is replaced by valine. 

As can be seen, the codons for glutamic acid (GAA and GAG) are very similar to two of the codons (GUA and GUG) for valine. Replacement of adenine in the glutamic acid codons by uracil causes valine to be incorporated into hemoglobin instead of glutamic acid and is responsible for the sickle cell trait. 

Figure 3.4 Hemoglobin transports oxygen and has a quaternary structure that shows how the chains arrange to form the molecule. As shown above, it consists of four polypeptide chains—two identical alpha globin (blue) and two identical beta globin (yellow)—each carrying a heme group (white) with a central iron atom, which bonds to oxygen. The green structure represents the amino acid glutamic acid at residue 6 on the beta chain.

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