To convert a DNA template strand into mRNA, use complementary base pairing. The RNA produced during transcription therefore has a base sequence complementary to the DNA template.
| DNA template base | mRNA base |
|---|---|
| A | U |
| T | A |
| C | G |
| G | C |
Converting a sequence
- Check that the sequence shown is the DNA template strand.
- For each template base, write the RNA nucleotide that would pair with it.
- Remember that RNA contains uracil (U) instead of thymine.
- Divide the completed mRNA sequence into groups of three to identify its codons.
The non-template DNA strand corresponds to the RNA sequence, except that DNA uses thymine in positions where RNA uses uracil.
Exam Tip: Identify the DNA strand before converting it. A template-strand sequence must be complemented to obtain mRNA; merely changing T bases to U would give the wrong answer.