Hemoglobin is a protein and has two distinct types of polypeptide chains. These are called the alpha and beta subunits. The gene that code for the beta chain undergoes a mutation in a single base that causes sickle cell anemia. Here, adenine base in the genetic code for glutamic acid is substituted with a thymine base.
The genetic code for glutamic acid in the beta chain gene is GAG. The "A" is replaced with "T" and the new code "GTG" codes for valine. Therefore, the mutated hemoglobin has valine in place of glutamic acid. This makes these mutated protein molecules to form aggregates resulting in a change in the shape of RBCs carrying them.
