![]() The molecule, therefore, has about 600 amino acids. What is most remarkable to consider is that a hemoglobin molecule is made up of two alpha chains and two beta chains that each consist of about 150 amino acids. ![]() Specifically, the amino acid glutamic acid is substituted by valine in the β chain. In sickle cell anemia, the hemoglobin β chain (a small portion of which is shown in Figure 2) has a single amino acid substitution, causing a change in protein structure and function. A change in nucleotide sequence of the gene’s coding region may lead to a different amino acid being added to the growing polypeptide chain, causing a change in protein structure and function. The unique sequence for every protein is ultimately determined by the gene encoding the protein. In sickle cell hemoglobin, this glutamate is replaced by a valine. In normal hemoglobin, the amino acid at position seven is glutamate. The beta chain of hemoglobin is 147 residues in length, yet a single amino acid substitution leads to sickle cell anemia.
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