RNA polymerase moves along the DNA in which direction during transcription?

• A. 3' to 5'
• B. 5' to 3'
• C. Both directions
• D. It does not move along DNA

Answer: (A)

RNA polymerase reads the DNA template strand in the 3' to 5' direction. It must move in this direction so that it can add nucleotides complementary to the template and build the RNA in the 5' to 3' direction. As transcription proceeds, the enzyme travels downstream from the promoter along the template, extending the RNA chain at its 3' end. This antiparallel arrangement means the RNA sequence is the complement of the template (and nearly identical to the coding strand, with U replacing T). So the movement along DNA is 3' to 5' on the template strand.