Final answer:
The amino acid sequence of each hemoglobin subunit is vital because a single alteration can significantly impact the protein's function and structure, as evidenced by sickle cell anemia where a single substitution leads to dysfunctional red blood cells and reduced life expectancy.
Step-by-step explanation:
The amino acid sequence coding for each hemoglobin subunit is crucial because it determines the protein's ultimate structure and function. For instance, in the case of sickle cell anemia, the β chain of hemoglobin experiences a single amino acid substitution—glutamic acid is replaced by valine. This simple alteration, out of the approximately 600 amino acids in the hemoglobin molecule, results in significant changes in the shape and function of red blood cells—turning them into sickle shapes that impede blood flow and decrease the individual's life expectancy. The fact that this change results from a single nucleotide mutation (a point mutation) in the gene encoding hemoglobin highlights the critical importance of accurate amino acid sequencing in proteins.