Question

1. a mutation in dna inserts a thymine, as shown below.

original dna sequence: tatgactgaa
mutated dna sequence: tatgaatctgaa
compared to a protein produced by the original dna sequence, a protein produced by the mutated sequence will differ in —
options:

• all amino acids that come after the t
• all of the amino acids
• the amino acids that come before the t
• a single amino acid

Explanation:

When a nucleotide (here, a T is inserted) is added to a DNA sequence, it causes a frameshift mutation. A frameshift mutation changes the reading frame of the codons (groups of 3 nucleotides that code for amino acids) starting from the point of insertion. So all the codons (and thus the amino acids they code for) after the insertion point will be different, because the grouping of nucleotides into codons is shifted. The original DNA sequence is TATGACTGAA, and the mutated one is TATGATCTGAA (insertion of T). The insertion is in the middle, so all amino acids after the insertion site will be affected. The option "all amino acids that come after the T" is correct because the frameshift alters the codon reading frame for all subsequent codons. The "all of the amino acids" is incorrect because the ones before the insertion (if any, in this case, the first few codons before the insertion) might not be affected, but here the insertion is early enough that most after are affected. "the amino acids that come before the T" is wrong as insertion doesn't affect before. "a single amino acid" is wrong because it's a frameshift, not a point mutation that changes one codon (a point mutation like substitution might change one amino acid, but insertion is frameshift).

Answer:

The correct option is: all amino acids that come after the T