Question

A gene that codes for one of the polypeptide chains of the blood proteins hemoglobin lies on chromosome 11 in humans. A substitution mutation in that gene causes the amino acid valine to be incorporated into hemoglobin in a place where glutamic acid would normally lie. The result is sickle cell disease. Explain how a change in a single base in DNA can bring about such a serious disorder.

Answer 1

A point mutation (base substitution) in the genetic information changes the genetic code, therefore the codon, therefore the amino acid that the genetic information is translated into. Changing the primary structure of a protein even minorly can change the secondary and tertiary structure of the protein; (remember shape dictates function) so that it causes the protein to not function correctly. Hemoglobin carries oxygen in the red blood cells so not correctly functioning hemoglobin causes the symptoms of sickle cell disease.