What is the term for the way nucleotides are grouped into codons during translation?

• A. The start of transcription.
• B. Reading frame, the way nucleotides are grouped into codons.
• C. A promoter region.
• D. The set of ribosomal RNAs.

Answer: (B)

The main idea here is how the messenger RNA is read in fixed groups of three nucleotides during translation. This fixed grouping is called the reading frame. The ribosome translates mRNA by scanning in triplets, or codons, starting at a defined point (the start codon) and moving along in steps of three nucleotides. Because the frame stays the same as translation proceeds, each codon reliably corresponds to a specific amino acid or a stop signal. If the reading frame were shifted, every downstream codon would be read differently, producing a completely different protein—this is why frameshifts can have drastic effects. The other terms listed—promoter regions involved in starting transcription, or ribosomal RNAs that are part of the ribosome—do not describe how nucleotides are grouped into codons during translation.