In order to determine the base sequence of the DNA gene that originally produced the mRNA codon "AGU," we need to consider the conventions of transcription, which includes the following:
- DNA is transcribed into mRNA, and during this process, adenine (A) pairs with uracil (U) in RNA (instead of thymine, T, which pairs with adenine in DNA).
- The base pairs for mRNA codons consist of the DNA template strand being complementary to the mRNA.
Given that the mRNA codon is "AGU," we can deduce the complementary DNA template strand:
- mRNA: A G U
- DNA template strand: T C A (since A pairs with T, G pairs with C, and U in mRNA corresponds to A in the DNA template strand)
The question asks for the DNA gene sequence that would produce mRNA "AGU," which corresponds to the coding strand (the strand that has the same sequence as the mRNA but with T instead of U).
So, the coding strand, which is not what we are directly asked to find, is:
- DNA coding: A T C (because U goes to T).
However, the actual answer options provided lead us to find the original one:
- Given the template strand "TCA," it matches with the transcribed mRNA codon.
Thus, among the options: A. UCA (incorrect) B. AGU (incorrect) C. TCC (incorrect) D. Tca (incorrect since it must be in uppercase for standard sequence)
The closest correct option that refers to the base sequence of the DNA corresponding to the mRNA codon supplied (assuming they were making a simplified form with different case for mRNA and shouldn't have), it would actually come from the complimentary form is the correct DNA strand would be C. TCC.
Therefore, while all answers reflect some information, strictly speaking, the correct answer coded or represented should be TCA, which converted would reflect upon bases matched to codon original strand correctly.