Transcription: Synthesis of RNA

• Transcription is the synthesis of RNA from a DNA template.
• The enzyme RNA polymerase transcribes genes into a single-stranded RNA.
• The RNA produced is complementary to one of the strands of DNA, which is known as the template strand. The other DNA strand is the coding, or sense strand.
• Bacteria contain a single RNA polymerase; eukaryotic cells utilize three different RNA polymerases.
• The DNA template is copied in the 3' to 5' direction and the RNA transcript is synthesized in the 5' to 3' direction.
• In contrast to DNA polymerases, RNA polymerases do not require a primer to initiate transcription, nor do they contain error-checking capabilities.
• Promoter regions, specific sequences in DNA, determine where on the DNA template RNA polymerase binds to initiate transcription.
• Transcription initiation requires a number of protein factors to allow for efficient RNA polymerase binding to the promoter.
• Other DNA sequences, such as promoter-proximal elements and enhancers, affect the rate of transcription initiation through the interactions of DNA-binding proteins with RNA polymerase and other initiation factors.
• Eukaryotic genes contain exons and introns. Exons specify the coding region of proteins, whereas introns have no coding function.
• The primary transcript of eukaryotic genes is modified to remove the introns (splicing) before a final, mature mRNA is produced.