Lac Operon

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Lac Operon

  1. 1. The lac Operon Review for BIOL 112
  2. 2. Escherichia coli (for the curious) <ul><li>“ Escherichia coli is a Gram-negative, non-sporulating, facultative anaerobic bacterium that is commonly found in the lower gastrointestinal tract of warm-blooded animals.” </li></ul><ul><li>- Wikipedia </li></ul>
  3. 3. Escherichia coli This is the mapped genome of the E. coli bacteria. Note the lac operon.
  4. 4. Operons <ul><li>“ An operon is a functioning unit of key nucleotide sequences including an operator , a common promoter , and one or more structural genes , which are controlled as a unit to produce messenger RNA (mRNA), in the process of protein transcription.” </li></ul><ul><li>- Wikipedia </li></ul>Promoter P/O Overlap Operator Coding Region T-Terminator
  5. 5. lac Operon <ul><li>“ The lac operon is an operon required for the transport and metabolism of lactose … It consists of three adjacent structural genes, a promoter, a terminator, and an operator. The lac operon is regulated by several factors including the availability of glucose and of lactose.” </li></ul><ul><li>-Wikipedia </li></ul>
  6. 6. Environmental Regulation <ul><li>The lac operon is environmentally regulated . This means that external stimuli will affect whether or not it is expressed. </li></ul><ul><li>In this case, the presence of lactose changes the conformation of LacI to bind to the P/O overlap region, blocking RNAP from creating mRNA for the lac operon. </li></ul><ul><li>NB: LacI is not synthesized from the lac operon, it is on a separate part of the genome! </li></ul>
  7. 7. lac Operon The RNAP binds at the promoter region, then travels along the operator and the coding regions for lacZ, lacY and lacA. However, note that the P/O overlap has a binding site for a repressor . A repressor will “get in the way” of RNAP.
  8. 8. lac Operon (with Lactose) RNAP LacZ LacY LacA KEY IDEA: THERE IS LACTOSE! Lactose can be digested!
  9. 9. lac Operon (without Lactose) RNAP LacI KEY IDEA: THERE ISN'T LACTOSE! No lactose to digest!
  10. 10. Disclaimer <ul><li>Please refer to the custom notes for a more detailed explanation of this mechanism! </li></ul>

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