Basic Concepts of RNA Biosynthesis (Transcription)

  1. All eukaryotic cellular RNAs are synthesized using a DNA template and a DNA-dependent RNA polymerase.
  2. Synthesis proceeds in a 5' to 3' direction.
  3. The three major types of cellular RNAs (ribosomal, transfer and messenger) are first synthesized as large molecular weight precursors which are processed specifically to produce the final mature RNA species.  
  4. The initiation step of transcription is especially highly regulated.  

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RNA Polymerases

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In prokaryotes, a single type of enzyme is responsible for the synthesis of all three types of cellular RNA species

In eukaryotes, four types of RNA polylmerase, each responsible for synthesis of a specific cellular RNA species. Abbreviations are: RNA polymerase I, pol I; RNA polymerase II, pol II; RNA polymerase III, pol III.

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