That's the protein in red blood cells that carries oxygen to the tissues of the body. So, sickle cell disease interferes with the delivery of oxygen to the tissues. Red blood cells with normal hemoglobin are smooth, disk-shaped, and flexible, like doughnuts without holes. They can move through the blood vessels easily.
So, due to change in the structure of protein, cells are not able to do their work properly. It means that protein structure is very important for its proper functioning and functioning of the cell.