Which statement correctly describes the amino acid substitutions of HbC and HbS relative to normal adult hemoglobin?

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Multiple Choice

Which statement correctly describes the amino acid substitutions of HbC and HbS relative to normal adult hemoglobin?

The key point is that these substitutions occur at the sixth amino acid of the beta-globin chain in normal adult hemoglobin. Normal HbA has glutamic acid at this position. In HbS, that glutamic acid is replaced by valine, and in HbC, it is replaced by lysine. So the accurate description is that HbC has lysine replacing glutamic acid, while HbS has valine replacing glutamic acid. This change at the same position—from a negatively charged glutamate to a positively charged lysine or a hydrophobic valine—accounts for the distinct properties of these hemoglobin variants.

The key point is that these substitutions occur at the sixth amino acid of the beta-globin chain in normal adult hemoglobin. Normal HbA has glutamic acid at this position. In HbS, that glutamic acid is replaced by valine, and in HbC, it is replaced by lysine. So the accurate description is that HbC has lysine replacing glutamic acid, while HbS has valine replacing glutamic acid. This change at the same position—from a negatively charged glutamate to a positively charged lysine or a hydrophobic valine—accounts for the distinct properties of these hemoglobin variants.

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