A tRNA comes in at A and leaves from E
- The idea
- Predict
- See it
- Why
- Check
The idea
“A new tRNA comes in at E, for entry, or at P, where the chain is.”
With three letters and no obvious order, E for entry is a fair guess. So is P, where the chain is.
The short version
The mistake: A new tRNA comes in at E, for entry, or at P, where the chain is.
What's actually true: During elongation, each tRNA arrives at the A site, shifts to the P site, and leaves from the E site.
- A, the aminoacyl site, takes a tRNA carrying an amino acid. P, the peptidyl site, holds the tRNA with the chain. E is the exit.
- A tRNA changes sites only when the ribosome shifts one codon, a step called translocation. One shift takes it from A to P, the next from P to E.
- The first tRNA, carrying methionine, is the exception. It starts in P when translation begins.
On the exam: In at A, over to P, out from E. E is for exit.