Which amino acid substitution in the hemoglobin beta chain causes sickle cell anemia?

1. The unique sequence of a protein is determined by the gene encoding it. 2. A change in the nucleotide sequence of the coding region can put a different amino acid into the chain. 3. In sickle cell anemia the hemoglobin beta chain carries a single amino acid substitution. 4. Specifically, glutamic acid is substituted by valine. 5. Because of that one change, hemoglobin molecules form long fibers that distort the biconcave red blood cells into a crescent shape. 6. Reading the substitution backwards, with valine replaced by glutamic acid, describes correcting the disease rather than causing it. 7. Glycine and asparagine are the terminal residues of the insulin A chain, so that pair belongs to a different worked example. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 3 "Biological Macromolecules", section 3.4 Proteins_