Each new base pairs with the one across from it
- The idea
- Predict
- See it
- Why
- Check
The idea
“The partner strand, or the RNA made from a gene, has the same bases as the strand it's built on.”
Replication copies DNA, so it seems each new strand should copy the strand it's built on. It ends up matching the other old strand instead.
The short version
The mistake: The partner strand, or the RNA made from a gene, has the same bases as the strand it's built on.
What's actually true: Each base in a partner strand or transcript pairs with the base across from it. A goes with T, or U in RNA, and G with C.
- A pairs with T and G with C, held together by hydrogen bonds. This is complementary base pairing, so each base sets the one across from it.
- So in replication, the new strand built on one old strand ends up with the same sequence as the other old strand.
- Transcription and translation follow the same rule. RNA uses uracil instead of thymine, so a template A gives a U in mRNA. A codon pairs with its tRNA anticodon too.
- Each strand's A count matches its partner's T count, and its G count matches the partner's C. So the two strands usually differ in makeup.
On the exam: Never copy straight across. Swap each base for its partner.