Frameshift mutations may involve _.?
Group of answer choices
A the substitution of nucleotides
B the substitution of codons
C the substitution of amino acids
D the insertion of one to several base pairs
E mutations in the promoter
The Correct Answer and Explanation is :
Correct Answer:
D. the insertion of one to several base pairs
Explanation:
Frameshift mutations are a specific type of mutation that alter the reading frame of the genetic code during protein synthesis. To understand why the correct answer is “D. the insertion of one to several base pairs,” we need to examine the nature of frameshift mutations in detail:
1. Genetic Code and Reading Frame
The genetic code is read in triplets of nucleotides called codons, each of which specifies an amino acid during translation. For example, a sequence of RNA like AUG-CGU-GCA corresponds to three codons.
2. Frameshift Mutation Defined
A frameshift mutation occurs when the number of nucleotides inserted or deleted is not a multiple of three. This shifts the reading frame, causing the ribosome to read codons incorrectly from the mutation point onward. The result is often a completely different and nonfunctional protein because the sequence of amino acids changes drastically or a premature stop codon is introduced.
3. Why D Is Correct
The insertion (or deletion) of one to several base pairs disrupts the triplet codon reading frame:
- If a single base pair is added (e.g.,
AUG-CG**U**-GCAbecomesAUG-C**GU**-UGC-A...), the frame shifts, altering every codon following the insertion. - This is also true for the insertion of two or four nucleotides.
4. Why the Other Choices Are Incorrect
- A. Substitution of nucleotides: Substitutions affect only a single codon and do not shift the reading frame.
- B. Substitution of codons: Codon substitutions result from nucleotide substitutions but do not cause a frameshift.
- C. Substitution of amino acids: Amino acid changes occur due to codon changes, not reading frame alterations.
- E. Mutations in the promoter: Promoter mutations affect transcription initiation but do not directly impact the reading frame.
Thus, frameshift mutations uniquely involve insertions or deletions, making D the correct answer.