Which hemoglobinopathy is characterized by abnormal structure and ability to carry oxygen?

The condition characterized by an abnormal structure of hemoglobin leading to issues with oxygen transport is sickle cell disease. Sickle cell disease results from a mutation in the HBB gene that causes hemoglobin to polymerize under low oxygen conditions, leading to the distortion of red blood cells into a characteristic sickle shape. This abnormality not only affects the ability of the red blood cells to carry oxygen effectively but also causes them to become stuck in blood vessels, resulting in pain and various complications.

Thalassemia, while also a hemoglobinopathy, primarily involves a deficiency in the production of one of the globin chains that make up hemoglobin, leading to anemia but not the same physical change in red blood cells as observed in sickle cell disease. Hemophilia is a bleeding disorder related to deficiencies in specific clotting factors and does not pertain to hemoglobin abnormalities. Tay-Sachs disease is a genetic disorder that affects lipid metabolism and is unrelated to hemoglobin structure or function.

Thus, the correct answer is sickle cell disease, as it is specifically associated with the abnormal structure of hemoglobin and its impaired ability to transport oxygen.