Interpret directional DNA, RNA processing and a supplied genetic code.
Method and worked examples
Transcription builds RNA complementary to a DNA template. The coding DNA strand matches the RNA sequence in the same direction, except T replaces U. In eukaryotes, transcription occurs in the nucleus; introns are removed and exons joined during RNA processing. Some genes produce functional RNA rather than protein.
Translation reads mRNA 5′ to 3′ at a ribosome. tRNAs carry amino acids and use complementary anticodons; rRNA has structural and catalytic roles. Start with the labelled strand, convert to mRNA and group bases in the stated frame. Use the supplied codon meanings to find the peptide. A stop codon ends translation and does not add an amino acid.
Example 1
Coding DNA is 5′−ATG GAA TGA−3′. Use AUG= Met, GAA= Glu and UGA= stop.
The mRNA is 5′−AUG GAA UGA−3′. Translation produces Met–Glu and then stops; stop is not a third amino acid.
Example 2
A primary RNA contains exon A, intron X and exon B. What remains after splicing?
Exons A and B are joined while intron X is removed. This changes RNA processing, not the underlying DNA sequence.
Watch out:They pair complementarily and antiparallel, so their aligned sequences differ.
From genes to polypeptides | Year 12 Biology | Ascent Arcade