A gene's mRNA is normally read in codons as: AUG-CCG-GAA-UCU... A mutation deletes one nucleotide early in the sequence (a deletion of 1 base). Which outcome is most likely for the resulting protein?
- Only one amino acid will change, and the rest of the protein will be unchanged.
- The reading frame will likely shift, changing many amino acids after the deletion and possibly creating an early stop codon. (correct answer)
- The mutation will increase the amount of protein made but not change its amino acid sequence.
- Deletion mutations are always silent because the genetic code has redundancy.
Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none), and some substitutions are 'silent' (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid); (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons; the sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! Here, the deletion of one base early in the mRNA sequence disrupts the grouping of bases into codons, shifting the reading frame and likely altering all subsequent amino acids. Choice B correctly identifies that the reading frame will likely shift, changing many amino acids after the deletion and possibly introducing an early stop codon, leading to a severely altered protein. On the other hand, choice A is wrong because a single-base deletion affects more than just one amino acid due to the frameshift, not preserving the rest of the sequence. You're doing awesome—use the strategy of visualizing codon triplets to predict effects: frameshifts from ins/del not multiples of three are most severe, often garbling the whole protein like in your example! Mutation location matters too, with early changes causing bigger disruptions, so keep practicing to master how DNA tweaks influence biology!