In sickle cell anemia, sickle shape occurs due to polymerization of

B. i.e. (Deoxyhemoglobin) (205 - U. satyanarayan 3rd)* Sickling is due to polymerization of deoxy HbS, Therefore if HbS is maintained in the oxygenated form (or with minimum deoxy HbS) sickling can be prevented.* The sticky patch of one deoxy HbS binds with the receptor of another deoxy HbS and this process continous resulting in the formation of long aggregate molecules of deoxy HbS. Thus the polymerization of deoxy HbS molecules leads to long fibrous precipitates these stiff fibres distort the erythrocytes into a sickle or cresent shape. The sickled erythrocytes are highly vulnerable to lysis* Basic defect in HbS is - altered solubility**