To determine the base sequence of the DNA gene that corresponds to the mRNA codon AGU, we need to remember that mRNA is synthesized from the DNA template strand through a process called transcription. During this process:
- Adenine (A) on DNA pairs with Uracil (U) in RNA (since RNA contains uracil instead of thymine).
- Thymine (T) on DNA pairs with Adenine (A) in RNA.
- Cytosine (C) on DNA pairs with Guanine (G) in RNA.
- Guanine (G) on DNA pairs with Cytosine (C) in RNA.
The mRNA codon "AGU" corresponds to the DNA template strand nucleotide sequence "TCA" (because A pairs with T, G pairs with C, and U pairs with A).
Since DNA is double-stranded and the base sequence of the coding strand is complementary to the template strand, we will reverse the transcription rules.
- The mRNA codon is AGU (A, G, U).
- The corresponding DNA template strand is TCA (T, C, A).
- The DNA coding strand (which has the same sequence as mRNA but with T instead of U) is ACT.
So, the final base sequence of the DNA gene that produced the mRNA codon AGU would be:
ACT (representing the coding strand).
From the options you provided, none match this specific sequence. The correct sequence is ACT.
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