Jody P. answered 01/26/22
Experienced high school tutor specializing in AP Biology
A DNA molecule consists of two complementary strands of nucleotides that run antiparallel to one another, that is one strand is 5' to 3' and the other strand is 3' to 5'. The 5' and 3' directionality comes from the orientation of the 5 carbons in the pentose sugar (deoxyribose in DNA or ribose in RNA) found in each nucleotide. During transcription, the enzyme RNA Polymerase reads the template strand of DNA in the 3' to 5' direction and builds the new strand of RNA in the 5' to 3' direction. To answer this question, you need to "think like RNA Polymerase." If the template strand is 5'-AGT-3', you need to read it from the 3' end, so 3'-TGA-5'. Then you build the new mRNA: 5'-ACU-3'.
The coding strand (or sense strand) on the DNA is complementary to the template, so it reads: 5'-ACT-3'.
The non-coding stand (or antisense strand) on the DNA is the template, so it reads: 3'-TGA-5'.
Emma D.
Hi Kathryn,
Here is how mRNA is created: coding DNA gets transcribed to template DNA, then template DNA gets transcribed to mRNA.
It is important to remember that 5' ends get "transcribed" to 3' ends. So the template DNA 5'AGT3' is transcribed to the mRNA 3'UCA5'. But since it is customary to write codons from 5'-end to 3'-end, the mRNA codon is actually ACU.
coding DNA: 5' ACT 3'
template DNA: 3' TGA 5'
mRNA: 5' ACU 3'
Hope this helps!
12/05/12