RNA polymerase is a catalyst

• Catalysts influence the rate of a biochemical reaction

  • But not the direction

• Chemical reactions are reversible

  • RNA polymerase can unmake an mRNA strand
    • Just as easily as it can make one
    • Grab a pyrophosphate, attach to a base, and release

• The direction of the reaction depends on the relative concentrations of the pyrophosphates and triphosphates

  • More triphosphates than pyrophosphates: Make RNA
  • More pyrophosphates than triphosphates: Unmake RNA

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