10 lac operon

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10 lac operon

  1. 1. Are genes always being transcribed and translated?
  2. 2. Gene Expression Gene expression for all genes falls into one of two categories. 1. constitutive expression – genes which are always turned on  1. known as housekeeping genes induced expression – genes which are only turned on as needed
  3. 3. lac Operon lac - lactose operon – several genes in a sequence all controlled by a single promoter (mainly in prokaryotes; some eukaryotes) promoter gene 1 operator gene 2 gene 3
  4. 4. lac Operon Bacterial cells mainly use glucose as a source of energy. The lac operon is only turned on when glucose is absent, but lactose is present. lac Operon Animation
  5. 5. lac Operon Operon codes for three enzymes 1. β-galactosidase (lacZ gene)  enzyme which breaks down lactose 1. permease (lacY gene)  protein transporter which brings lactose into cell 1. transacetylase (lacA gene)  adds acetyl group to galactose
  6. 6. lac Operon The lacI gene codes for a separate repressor protein.
  7. 7. lac Operon repressor protein (lacI gene) binds to the operator portion in the presence of glucose prevents RNA polymerase from transcribing operator genes When do you want the repressor to bind / not bind to the operon?
  8. 8. When lactose is absent: enzymes are not needed to metabolise lactose repressor binds to the operator to inhibit transcription
  9. 9. When lactose is present: lactose binds to the repressor protein lactose-repressor complex cannot bind to the operator transcription can proceed
  10. 10. lac Operon Since lactose is the molecule that determines when the operon is turned on or off, it is known as an effector molecule. effector molecule – any molecule that can regulate the activity of a protein inducer – effector molecule that binds repressor protein to cause it to fall off operator
  11. 11. lac Operon Animation lac Operon Animation

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