1. KEY CONCEPT Transcription converts a gene into a single-stranded RNA molecule.

2. The transcription process is similar to replication.
Transcription and replication both involve complex enzymes and complementary base pairing.
The two processes have different end results.
Replication copies all the DNA; transcription copies a gene.
Replication makes one copy; transcription can make many copies.
growing RNA strands
DNA
one
gene

3. Transcription is catalyzed by RNA polymerase.
RNA polymerase and other proteins form a transcription complex.
The transcription complex recognizes the start of a gene and unwinds a segment of it.
start site
nucleotides
transcription complex

4. Process takes place in 3 stages – initiation, elongation, termination

5. Initiation – RNA polymerase attaches to specific promoter region

6. Elongation – RNA polymerase matches the appropriate RNA nucleotides to the DNA exposing the coding gene

7. RNA polymerase moves along the DNA
Nucleotides pair with one strand of the DNA.
RNA polymerase bonds the nucleotides together.
The DNA helix winds again as the gene is transcribed.
DNA
RNA polymerase moves along the DNA

8. Termination – RNA polymerase reaches the terminator region and the primary transcript is released

9. The RNA strand detaches from the DNA once the gene is transcribed.

10. When transcription is completed, a molecule called the primary transcript or pre mRNA is produced
The pre mRNA needs to be edited before it is a completed mRNA molecule

11. Primary transcript can contain 200,000 nucleotides, mRNA averages only 1000 nucleotides