The structural difference between a normal hemoglobin molecule and a sickle cell molecule-that dramatically decreases life expectancy-is a single amino acid of the 600. 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. In sickle cell anemia, the hemoglobin β chain has a single amino acid substitution, causing a change in both the structure and function of the protein. Any change in the gene sequence may lead to a different amino acid being added to the polypeptide chain, causing a change in protein structure and function. The unique sequence for every protein is ultimately determined by the gene that encodes the protein. The unique sequence and number of amino acids in a polypeptide chain is its primary structure. To understand how the protein gets its final shape or conformation, we need to understand the four levels of protein structure: primary, secondary, tertiary, and quaternary (Figure 2). \)ĭefine the different layers of protein structureĪs discussed earlier, the shape of a protein is critical to its function.
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