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Controlling Gene Expression

Controlling Gene Expression. Definitions. Gene – sequence of DNA that is expressed as a protein (exon) Genes are coded DNA → RNA → Protein → Trait Transcription – rewritting DNA into RNA which is needed for a gene to be expressed as a protein

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Controlling Gene Expression

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  1. Controlling Gene Expression

  2. Definitions • Gene – sequence of DNA that is expressed as a protein (exon) • Genes are coded • DNA→RNA→Protein→Trait • Transcription – rewritting DNA into RNA which is needed for a gene to be expressed as a protein • Operon – a sequence of DNA that will turn transcription on and off

  3. Parts of an Operon Operator Structural Genes • Regulatory gene • Repressor • Promoter

  4. Parts of an Operon • Promoter – site where RNA polymerase attaches to begin transcription • Operator – on/off switch • Repressor will attach turning off transcription • If repressor doesn’t fit into operator, RNA polymerase can transcribe structural genes • Transcription occurs

  5. Operator/Repressor • Lock n’ Key arrangement

  6. Inducible Operon • Transcription is normally off • Repressor is active • Fits into operator turning off transcription • Inducer • Molecule from the environment • Attaches to the repressor • Changes the shape of the repressor making it inactive.

  7. Inducible Operon • Repressor is active • RNA polymerase can not attach to promoter • No proteins are translated (synthesized)

  8. Inducer needs to be present to start transcription • i.e. inducer is lactose Transcription is on • The end proteins produced are enzymes • i.e. lactase

  9. Operon is off • Repressor is active • Transcription does not occur • Operon is on • Inactive repressor • Proteins (enzymes) are made

  10. Regulatory Gene makes an active repressor

  11. Repressor fits into operator stopping transcription

  12. When the inducer attaches to the repressor, the repressor changes shape. The repressor no longer fits into operator so RNA polymerase can transcribe mRNA. mRNA will make protein

  13. Inducible Animation Lac Operon

  14. Inducible Operon • Transcription is normally off • Repressor is active (fits into operator) • Need an outside molecule from environment to inactivate repressor • Inducer has the role of inactivating repressor • Proteins produced through transcription are enzymes. • Enzymes break down inducer. • Inducer is absent which makes repressor active again.

  15. Repressible Operon • Transcription is normally on • Repressor is inactive • Repressor does not fit into the operator • CoRepressor is needed to stop transcription • COREPRESSOR is the end protein produced by transcription • Structural protein used by the cell

  16. End product = corepressor

  17. Tryptophan is the corepressor

  18. Repressible Operon AnimationTrpytophan Operon

  19. Repressible Operon • Inactive repressor • The build up of the end product turns off transcription • Usually makes structural proteins • Proteins needed for cell function • When structural proteins are used up by the cell; the corepressor is absent • Transcription will turn on again.

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