Explain the concept of reading frame in translation.

• A. A frame of codons from a start codon; frameshifts alter codon grouping and protein.
• B. A frame of amino acids around start codon.
• C. The reading frame is universal across species.
• D. It has no biological significance.

Answer: (A)

Reading frame is the way the ribosome groups nucleotides into codons to build a protein. Translation reads mRNA in consecutive three-nucleotide units, starting at a start signal (AUG). This starting point sets the frame, so every downstream codon—and therefore every amino acid added—depends on that initial grouping. If the sequence is shifted by inserting or removing nucleotides, the grouping changes, and all downstream codons (and the resulting amino acids) change, often producing a nonfunctional protein or an early stop. On any given RNA strand, there are three possible reading frames, but only one is used to produce a specific protein, defined by where the start codon lies. Frameshifts therefore have a powerful impact on the final protein, highlighting why maintaining the correct reading frame is essential for proper gene expression.