A.  Prokaryotic Transcription
     1.  Bacterial DNA
          a.  Prokaryotes - no nucleus
          b.  DNA - One continuous, circular chromosome composed of double helical DNA
          c.  Structural Gene - segment of DNA containing information which codes for a protein

     2.  Process - prokaryotic transcription follows the same procedure as found in eukaryotes

**To review transcription and translation, please click on the following links before proceeding.

                               

                               

     3.  E. Coli Example
          a.  Regulation of Translation - most bacteria will only produce proteins when they are needed;  this prevents wasted energy and materials
          b.  Grow E. Coli on Glucose - the bacterium will only produce proteins necessary to catabolize glucose for energy
          c.  Grow E. Coli on Lactose - the bacterium will now begin producing proteins necessary to catabolize lactose for energy
                1)  Beta-galactosidase - enzyme which catabolizes the disaccharide lactose into glucose and galactose monosaccharides
                2)  Inducible - B-gal is only produced when it is needed
           d.  Jacob and Manod - conducted the first experiment producing evidence that even prokaryotes had the ability to regulate protein synthesis

B.  Lac Operon
      1.  Physical Description - segment of DNA found in some prokaryotes allowing for regulation over protein synthesis (translation)

      2.  Five Components
           a.  Promoter - specific segment of DNA to which RNA Polymerase attaches to begin transcription of mRNA from an operon
           b.  Operator - sequence of nucleotides located between the promoter and structural genes
           c.  Regulator - sequence of DNA found anywhere on the bacterial chromosome; codes for the production of repressor protein
           d.  Repressor - protein which can bind to the operator, thus inhibiting the promoter from binding, which, in turn, leads to NO transcription because RNA Polymerase was not able to bind or move along the DNA
           e.  Inducer - substance which can activate or inactive a repressor
                Example in Lac Operon:
                1)  Lactose is the inducer
                2)  If lactose is present, it binds to and inactivates the repressor by causing it to fall off the operator
                3)  If lactose operator is free of repressor, then RNA Polymerase is able to bind.
                4)  If RNA Polymerase can bind to the lac operon, then B-galactosidase is produced, and lactose is catabolized into glucose and galactose for energy

To test your knowledge about the lac operon, click on the Operon Questions Link at the top of this page.  After you answer the questions, be sure to check your responses by clicking on the Operon Answers Link.

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