A change in the primary structure of the β-globin polypeptide chain—meaning a change in the specific sequence of amino acids—can significantly affect its chemical properties because the primary structure determines how the protein folds and functions. Here is how this change impacts the β-globin chain:

• Amino Acid Properties and Folding: Each amino acid has a unique side chain (R group) with specific chemical properties such as polarity, charge, and hydrophobicity. A substitution of one amino acid for another can alter these properties in the chain. For example, replacing a hydrophilic amino acid with a hydrophobic one can change how the chain folds, as hydrophobic amino acids tend to cluster inside the protein away from water, while hydrophilic ones tend to be on the outside

• Secondary and Tertiary Structure Impact: The altered amino acid sequence affects hydrogen bonding and other interactions (ionic bonds, disulfide bonds, hydrophobic interactions) between side chains, which are crucial for the protein’s secondary (α-helices and β-pleated sheets) and tertiary structure (overall 3D shape). This can lead to changes in the protein’s shape and stability

• Functional Consequences: Since the β-globin chain is part of hemoglobin, which binds oxygen, changes in its structure can affect oxygen binding and transport. For instance, in sickle cell anemia, a single amino acid substitution (glutamic acid to valine) in the β-globin chain changes the chemical nature of the protein, causing hemoglobin molecules to aggregate abnormally and red blood cells to deform into a sickle shape, impairing their function

In summary, a change in the primary structure of the β-globin polypeptide chain alters the chemical properties of the amino acids involved, which affects the folding and final 3D structure of the protein, ultimately impacting its function such as oxygen transport in hemoglobin