10 lac operon-2010 update

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10 lac operon-2010 update

  1. 2. Gene Expression <ul><li>constitutive expression – genes which are always turned on </li></ul><ul><ul><li>known as housekeeping genes </li></ul></ul><ul><li>induced expression – genes which are only turned on as needed </li></ul>
  2. 3. lac Operon <ul><li>lac - lac tose </li></ul><ul><li>operon – several genes in a sequence all controlled by a single promoter (mainly in prokaryotes; some eukaryotes) </li></ul>promoter gene 1 gene 2 gene 3 operator
  3. 4. lac Operon <ul><li>Cells mainly use glucose as a source of energy. </li></ul><ul><li>The lac operon is only turned on when glucose is absent, but lactose is present. </li></ul><ul><li>lac Operon Animation </li></ul><ul><li>http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related </li></ul>
  4. 5. lac Operon Details <ul><li>Operon codes for 3 enzymes – found in E. coli </li></ul><ul><li>b-galactosidase ( lacZ gene) </li></ul><ul><ul><li>enzyme which breaks down lactose </li></ul></ul><ul><li>permease ( lacY gene) </li></ul><ul><ul><li>protein transporter which brings lactose into cell </li></ul></ul><ul><li>transacetylase ( lacA gene) </li></ul><ul><ul><li>adds acetyl group to galactose </li></ul></ul>
  5. 6. Repressor Protein <ul><li>repressor protein ( lacI gene) </li></ul><ul><ul><li>binds to the operator portion in the presence of glucose. </li></ul></ul><ul><ul><li>prevents RNA polymerase from transcribing genes when bound to operator </li></ul></ul><ul><ul><li>transcribed by a different gene from the lac operon </li></ul></ul><ul><li>When do you want to the repressor to bind / not bind to the operon? </li></ul>
  6. 7. <ul><li>When lactose is absent: </li></ul><ul><ul><li>enzymes are not needed to metabolise lactose </li></ul></ul><ul><ul><li>repressor binds to the operator to inhibit transcription </li></ul></ul>
  7. 8. <ul><li>When lactose is present : </li></ul><ul><ul><li>lactose binds to the repressor protein </li></ul></ul><ul><ul><li>lactose-repressor complex cannot bind to the operator </li></ul></ul><ul><ul><li>transcription can proceed </li></ul></ul>
  8. 9. Effector Molecules <ul><li>Since lactose is the molecule that determines when the operon is turned on or off, it is known as an effector molecule. </li></ul><ul><li>effector molecule – any molecule that can regulate the activity of a protein </li></ul><ul><li>inducer – effector molecule that binds repressor protein to cause it to fall off operator </li></ul>
  9. 11. lac Operon Animation <ul><li>lac Operon Animation </li></ul><ul><li>http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related </li></ul>

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