All of the following are true about Sickle cell disease, except: (A) Single nucleotide change results in change of Glutamine to valine, (B) RFLP results from a single base change, (C) 'Sticky patch' is generated as a result of replacement of a non polar residue with a polar residue, (D) HbS confers resistance against malaria in hetrozygotes
Answer is C. Sticky patches. The substitution of valine for glutamate at position 6 of the b chains of hemoglobin places a nonpolar residue on the outside of hemoglobin S, the version of hemoglobin responsible for sickle-cell anemia.The oxygen affinity and allosteric propeies of hemoglobin are viually unaffected by this change. However, the valine side chain of hemoglobin S interacts with a complementary sticky patch (formed by phenyl-alanine b85 and leucine b88) on another hemoglobin molecule--a patch that is exposed in deoxygenated but not in oxygenated hemoglobin. This mutation is the one that occurs in sickle-cell anemia. This alteration markedly reduces the solubility of the deoxygenated, but not the oxygenated, form of hemoglobin because the hemoglobin molecules interact with one another until a complex forms that is large enough that it cannot be solubilized. This complex precipitates and deforms the cell. Thus, sickling occurs when there is a high concentration of the deoxygenated form of hemoglobin S.