92. Which one of the following types of mutations can lead to a major change in the encoded
protein?
A. Insertion of a single nucleotide near the end of the coding sequence.
B. Removal of a single nucleotide from the beginning of the coding sequence.
C. Deletion of three consecutive nucleotides of a codon in the middle of the coding sequence.
D. Deletion of four consecutive nucleotides in the middle of the coding sequence.
A. A, D
B. B, D
C. B, C
D. A, E

Detailed Explanation:

Mutations in the DNA sequence can have a profound effect on the structure and function of the resulting protein. The impact of these mutations largely depends on their location and type within the coding sequence. Mutations can be classified into several categories, such as point mutations, insertions, deletions, and frameshift mutations, each contributing differently to the final protein.

Let’s analyze each mutation type:

1. Insertion of a Single Nucleotide Near the End of the Coding Sequence

   • An insertion of a single nucleotide near the end of the coding sequence can still cause significant changes, particularly if it shifts the reading frame and leads to a frameshift mutation.

   • However, near the end, this mutation might have a less drastic effect on the protein, as only the last few amino acids are affected.

2. Removal of a Single Nucleotide from the Beginning of the Coding Sequence

   • This would likely result in a frameshift mutation, affecting the entire protein sequence downstream of the mutation.

   • Frameshift mutations lead to the alteration of the reading frame and can result in the production of a completely nonfunctional protein or a protein with a significantly altered function.

3. Deletion of Three Consecutive Nucleotides of a Codon in the Middle of the Coding Sequence

   • Deletion of three nucleotides would remove an entire codon, which generally results in removing one amino acid from the protein sequence.

   • This type of mutation typically causes a minor change in the protein and is less likely to have a major effect unless the deleted amino acid is crucial for the protein’s function.

4. Deletion of Four Consecutive Nucleotides in the Middle of the Coding Sequence

   • Four nucleotide deletions would result in a frameshift mutation, which could change the entire sequence of amino acids downstream of the deletion.

   • This can have a major effect on the protein, potentially rendering it nonfunctional or significantly altering its function.

Which mutations lead to major changes?

• Mutations that result in frameshift mutations, such as removal of a single nucleotide from the beginning or deletion of four nucleotides, are more likely to result in a major alteration in the protein’s structure and function.

• On the other hand, removal of three nucleotides typically causes a minor change.

Correct Answer:

B. B, D