Multiple Choice
Which of the following mutations of the ras gene is most likely associated with cancer?
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15. Gene Expression
Mutations
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Which of the following mutations, occurring just after the start codon in the mRNA is likely to have the most serious effects on the polypeptide product?
A
Deletion of one codon.
B
Deletion of one nucleotide.
C
Insertion of three nucleotides.
D
Substitution of one nucleotide.
Verified step by step guidance1
Understand the role of the start codon in mRNA translation. The start codon (AUG) signals the beginning of protein synthesis, setting the reading frame for the ribosome.
Recognize the impact of different types of mutations on the reading frame. A deletion or insertion of nucleotides can shift the reading frame, potentially altering every subsequent amino acid in the polypeptide chain.
Consider the effect of a deletion of one nucleotide. This type of mutation causes a frameshift, changing the reading frame and likely resulting in a completely different and nonfunctional protein.
Compare the frameshift mutation to other types of mutations. A deletion of one codon or insertion of three nucleotides does not change the reading frame, as they involve complete sets of three nucleotides, which are the building blocks of codons.
Evaluate the substitution of one nucleotide. This mutation changes only one amino acid, potentially having a less severe effect compared to a frameshift mutation, which alters the entire sequence downstream.
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