Sickle-cell anemia is associated with a mutation in the gene encoding the beta subunit of hemoglobin that results in a change from glutamic acid to valine at position 6. All other amino acids are identical to a normal hemoglobin molecule.

Based on the information above, which of the following mutations is the most likely cause of sickle-cell anemia?

Question

Sickle-cell anemia is associated with a mutation in the gene encoding the beta subunit of hemoglobin that results in a change from glutamic acid to valine at position 6. All other amino acids are identical to a normal hemoglobin molecule.

Based on the information above, which of the following mutations is the most likely cause of sickle-cell anemia?

BlackTom AI · Accepted Answer

To approach this question, we start by identifying the molecular change described: a substitution of glutamic acid with valine at position 6 in the beta subunit of hemoglobin, with all other amino acids unchanged. This specific amino acid change is classic for sickle-cell anemia and points toward a nucleotide-level mutation in the beta-globin gene.
Option 1 states a single base-pair insertion in the beta-globin gene. An insertion would disrupt the reading frame (frameshift) and typically alter many downstream amino acids, not just a single substitution at one position; plus, sickle-cell features a precise single-residue change, so this is unlikely.
Option 2 suggests a translocation of DNA between chromosomes. Translocations involve large-scale rearrangements and would affect more than just one amino acid, often with severe, broader phenotypic consequences, not the isolated Glu-to-Val substitution described.
Option 3 proposes a single base-pair deletion in the beta-globin gene. A deletion would also cause a frameshift, altering multiple residues and likely producing a very different protein product, rather than a targeted Glu-to-Val swap at position 6.
Option 4 asserts a single base-pair substitution in the beta-globin gene. This is the precise, minimal change that can alter one codon from encoding glutamic acid (Glu) to encoding valine (Val) at position 6, matching the canonical sickle-cell mutation (a missense point mutation). It preserves the overall length of the protein while changing the amino acid at the critical position, explaining the disease phenotype.
In sum, the mutation best aligned with the described clinical and molecular details is a single base-pair substitution in the beta-globin gene, whereas the other options involve insertions, deletions, or larger chromosomal rearrangements that would produce different outcomes.

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