In sickle-cell disease, a glutamate -> valine substitution results in the formation of hb5 (sickle cell hemoglobin) molecules that: a. stabilize the wall of the red blood cell against oxidative damage b. aggregate abnormally to form fibers and cannot adequately carry oxygen c. have abnormally high affinity to bind oxygen d. cause high levels of repulsion between neighboring hb5 molecules

b. aggregate abnormally to form fibers and cannot adequately carry oxygen

Explanation:

The sickle cell hemoglobin is an abnormal form of hemoglobin. As the sickle cell hemoglobin release oxygen to the interstitial fluid, it forms long, stiff, and rod-like fibers. These aggregates of hemoglobin tend to bend the erythrocyte into a sickle shape. The sickled erythrocytes rupture easily and do not move easily through blood vessels. Sickled cells tend to stick together and form clumps which in turn cause blockages in blood vessels. Therefore, the presence of sickle cell hemoglobin adversely affects the ability of RBCs to carry oxygen.

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