Which of the following mRNA sequences codes for the amino acid sequence Ala-Asn-Tyr-Phe-His?

Question

BlackTom AI · Accepted Answer

The question asks which mRNA sequence encodes the amino acid sequence Ala-Asn-Tyr-Phe-His. To check each option, translate the codons (triplets) in order to see which amino acids they specify, using the standard genetic code.

Option 1: 5'-GCG-AAC-TAT-TTC-CAC-3'. Codons are GCG (Ala), AAC (Asn), TAT (note: in mRNA, thymine T should be uracil U; TAT would correspond to UAU in proper mRNA, which codes for Tyr), and TTC (Phe), CAC (His). However, the second, third, and subsequent codons do not align with the intended Tyr and Phe positions as written here if interpreted strictly as written with T's; also the sequence includes a thymine where RNA uses uracil. This makes it inconsistent with the target Ala-Asn-Tyr-Phe-His.

Option 2: 5'-UAUCCAUGGCACUUUAAAC-3'. Breaking into codons: UAU (Tyr), CCA (Pro), UUG (Leu), GCA (Ala), CUU (Leu), UAA (Stop), AC- remains incomplete. This sequence yields a completely different order and includes a stop codon; it does not produce Ala-Asn-Tyr-Phe-His.

Option 3: 5'-GCG-AAC-GAU-UUC-CAG-3'. Codons: GCG (Ala), AAC (Asn), GAU (Asp), UUC (Phe), CAG (Gln). This gives Ala-Asn-Dsp-Phe-Gln, not Ala-Asn-Tyr-Phe-His. The third codon is Asp instead of Tyr, and the last codon is Gln, not His.

Option 4: 5'-GCG-AAC-UAU-UUC-CAC-3'. Codons: GCG (Ala), AAC (Asn), UAU (Tyr), UUC (Phe), CAC (His). This exactly matches the target sequence Ala-Asn-Tyr-Phe-His in order.

In summary, only Option 4 provides codons that translate sequentially to Ala, Asn, Tyr, Phe, and His without mismatches or premature stop signals, while the other options introduce incorrect amino acids, stop codons, or improper RNA bases. The correct codon composition for the specified peptide is therefore found in Option 4.

Which of the following mRNA sequences codes for the amino acid sequence Ala-Asn-Tyr-Phe-His?单项选择题

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