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Protein Synthesis - PowerPoint PPT Presentation

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Protein Synthesis
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  1. Protein Synthesis Control Mechanisms

  2. Control Mechansisms • the human genome contains about 20000-25000 genes that code for proteins • housekeeping genes code for proteins that are always needed in a cell; they are constantly being transcribed and translated • not all proteins are needed by all cells at all times, so gene regulation is important to an organism's survival

  3. Control Mechansisms • in eukaryotic cells, there are 4 levels of gene regulation: • transcriptional • post-transcriptional • translational • post-translational *see Table 1 on page 255*

  4. Control Mechansisms • transcription factors are proteins that bind to DNA and assist RNA polymerase in binding to DNA to "turn on" genes when they are needed • prokaryotic cells use operons to control gene expression: -an operon is a cluster of genes with one promoter region, and a sequence of bases called an operator in between

  5. The lac operon • lactose is a disaccharide found in milk or milk sugars • intestinal bacteria cells split lactose (into glucose and galactose) to generate energy for growth using the enzyme beta-galactosidase

  6. The lac operon • the lac operon contains a promoter, an operator, and 3 genes: • lacZ codes for beta-galactosidase • lacY codes for beta-galactosidase permease (makes cell membrane permeable to lactose) • lacA codes for transacetylase (unknown function)

  7. The lac operon

  8. The lac operon • when there is no lactose present, the LacI protein binds to the operator, which partially blocks the promoter region, preventing RNA polymerase from binding to it • LacI is a repressor protein • when lactose is present, it binds to the LacI protein, changing its shape and causing it to fall off of the DNA • lactose is a signal molecule or inducer

  9. lac operon animation • Narrated animation:

  10. The trp operon • tryptophan is an amino acid needed for protein synthesis • intestinal bacteria cells can obtain tryptophan from a mammalian diet, or they can synthesize it themselves

  11. The trp operon • the trp operoncontains a promoter, an operator, and 5 genes: • the 5 genes code for 3 enzymes needed to synthesize tryptophan

  12. The trp operon • when there is no tryptophan present, the trprepressorprotein is not able to bind to the operator, and RNA polymerase is free to bind to the promoter and initiate transcription • when there is tryptophan present, it binds to the trp repressor protein, altering its shape so that it can bind to the operator; tryptophan is a corepressor

  13. trp operon animation • Narrated animation: