A single mutation causes sickle-cell disease. Which of the following statements best describes how this occurs?
A. The removal of several nucleotides cause the start codon to shift down several places. This causes RNA polymerase to bind in the incorrect spot so that several amino acids are left out of the polypeptide chain during translation. This results in a hemoglobin protein that is incorrectly formed, resulting in sickle-shaped red blood cells that cannot function as intended.
B. A single nucleotide mutation causes a normal glutamine amino acid to be replaced with a valine amino acid. This causes the resulting hemoglobin protein to form incorrectly, resulting in sickle-shaped red blood cells that cannot function as intended.
C. Three nucleotide mutations cause normal glutamine amino acids to be replaced with valine amino acids. This causes excess hemoglobin proteins to be synthesized, causing red blood cells to swell to the point of bursting, resulting in burst cells that have a sickle-shape.
D. The addition of several nucleotides cause the start codon to shift down several places. This causes RNA polymerase to bind in the incorrect spot so that several extra amino acids are included in the polypeptide chain during translation. This results in a hemoglobin protein that is incorrectly formed, resulting in sickle-shaped red blood cells that cannot function as intended.
Answer: B
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