STEP 2 Transcription always proceeds along the same DNA strand called the template strand . RNA polymerase moves down the DNA template strand in the 3 ’ to 5 ’ direction . As it does so , it creates the RNA strand by progressively stringing together nucleotides in a 5 ’ to 3 ’ direction , at a rate of approximately 40 nucleotides per second . The RNA strand is complementary to the template strand and is therefore almost identical ( except for the uracil base in place of thymine ) to the other DNA strand , called the nontemplate strand .
This process is called elongation . As elongation proceeds , DNA is simultaneously unwound ahead of the RNA polymerase and rewound behind it . The region of unwinding and rewinding is called a transcription bubble . As the RNA elongates , it peels away from the DNA template .
STEP 3 RNA cannot perform its assigned function within a cell until elongation ends and the newly synthesized RNA strand separates from the DNA template . This process is referred to as termination .