Reading a coding sequence: For the RNA 5′-GAU GGU UGA UGU-3′, how many amino acids are translated before termination (standard code, single reading frame)?

Introduction / Context:Decoding an mRNA requires grouping nucleotides into codons and applying the standard genetic code, including recognition of stop codons that terminate translation.

Given Data / Assumptions:

• Sequence is 5′-GAU GGU UGA UGU-3′.
• Translation starts at the first codon shown and proceeds in-frame.
• Standard genetic code applies; no reinitiation after a stop.

Concept / Approach:Translate codons left to right: GAU, GGU, UGA, UGU. GAU codes Aspartate; GGU codes Glycine; UGA is a stop signal; translation halts upon encountering UGA, so codons after the stop are not translated.

Step-by-Step Solution:

Verification / Alternative check:Check a codon table: UGA is one of the three termination codons (UAA, UAG, UGA). No further elongation occurs after a stop in a single continuous ORF.

Why Other Options Are Wrong:

• One: ignores the first two sense codons.
• Three or Four: incorrectly translate past the stop codon.

Common Pitfalls:Reading out of frame, forgetting that translation stops at the first in-frame stop, or assuming reinitiation within the same short stretch.

Final Answer:Two