Neighboring genes can be read in opposite directions
- The idea
- Predict
- See it
- Why
- Check
The idea
“One strand is the template for every gene, so all genes are read the same way.”
Most diagrams show one gene, read left to right off the bottom strand. It's easy to picture the whole chromosome that way.
The short version
The mistake: One strand is the template for every gene, so all genes are read the same way.
What's actually true: Each gene's template can be either strand, so genes side by side can be read in opposite directions.
- RNA polymerase reads its template strand 3' to 5' and builds RNA 5' to 3'. The other strand, the coding strand, matches the RNA, with U for T.
- A promoter is where the polymerase binds before a gene. It points one way, so it sets the template strand and the direction.
- Promoters can face either way, so both strands are templates somewhere along a chromosome.
On the exam: Each gene picks its own template strand. Polymerase reads it 3' to 5', so direction follows the strand.