AP BiologyCommon mistakesRNA polymerase reads its template 3' to 5'

RNA polymerase reads its template 3' to 5'

  1. The idea
  2. Predict
  3. See it
  4. Why
  5. Check

The idea

“RNA polymerase reads the template 5' to 3', the same way the sequence is written.”

Sequences are written 5' to 3', so it's natural to picture the enzyme reading that way. The RNA sets the direction, and it only grows at its 3' end.

The short version

The mistake: RNA polymerase reads the template 5' to 3', the same way the sequence is written.

What's actually true: RNA polymerase reads its template 3' to 5' and builds the RNA 5' to 3', adding each nucleotide to the 3' end.

  1. RNA polymerase adds each nucleotide to the RNA's 3' end, so RNA is built 5' to 3'.
  2. The RNA pairs antiparallel with its template, so the template is read 3' to 5'.
  3. On the page, find which end of the template is 3'. The enzyme travels away from that end, toward the 5' end.

On the exam: Read the template 3' to 5'. The RNA it makes grows 5' to 3'.

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