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GENE REGULATION

Colorized SEM 7,000 . Figure 11.1A. GENE REGULATION. 0. 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes Early understanding of gene control Came from studies of the bacterium Escherichia coli. 0. The lac Operon

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GENE REGULATION

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  1. Colorized SEM 7,000 Figure 11.1A GENE REGULATION 0 • 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes • Early understanding of gene control • Came from studies of the bacterium Escherichia coli

  2. 0 • The lac Operon • In prokaryotes, genes for related enzymes • Are often controlled together in units called operons The Lac operon produces proteins responsible for lactose utilization – so the cell can use lactose So if you were a cell, and lactose was present, would you want these genes turned ON or OFF?

  3. 0 Operon turned off (lactose absent) OPERON Regulatorygene Promoter Operator Lactose-utilization genes DNA mRNA RNA polymerasecannot attach topromoter Activerepressor Protein Operon turned on (lactose inactivates repressor) RNA polymerasebound to promoter DNA mRNA Protein Inactiverepressor Enzymes for lactose utilization Lactose Figure 11.1B • Regulatory proteins bind to control sequences in the DNA and turn operons on or off in response to environmental changes

  4. Promoter Operator Genes DNA Activerepressor Activerepressor Tryptophan Inactiverepressor Inactiverepressor Lactose Figure 11.1C lac operon trp operon 0 • Other Kinds of Operons • The trp operon • Is similar to the lac operon, but functions somewhat differently

  5. Muscle cell Pancreas cells Blood cells Figure 11.2 EUKARYOTIC GENE EXPRESSION 0 • 11.2 Differentiation yields a variety of cell types, each expressing a different combination of genes • In multicellular eukaryotes • Cells become specialized as a zygote develops into a mature organism

  6. NUCLEUS Chromosome DNA unpacking Other changes to DNA Gene Gene Transcription Exon RNA transcript Intron Addition of cap and tail Tail Splicing mRNA in nucleus Cap Flow throughnuclear envelope mRNA in cytoplasm CYTOPLASM Breakdown of mRNA Broken-downmRNA Translation Polypeptide Cleavage / modification / activation Active protein Breakdownof protein Broken-downprotein Figure 11.9 Overview of Gene Regulation in Eukaryotes DNA Packaging Transcription Regulation Post-Transcriptional Modification - Splicing and other additions mRNA degredation Post-Translational Modification -Cleavage, addition of functional groups

  7. 0 • 11.4 DNA packing in eukaryotic chromosomes helps regulate gene expression Wound around clusters of histone proteins, forming a string of beadlike nucleosomes

  8. Enhancers Promoter Gene DNA Activatorproteins Transcriptionfactors Otherproteins RNA polymerase Bendingof DNA Figure 11.6 Transcription 0 • 11.6 Complex assemblies of proteins control eukaryotic transcription Proteins involved in Transcription Control: Transcription Factors – act at site of the promoter Activators – bind to the enhancer region of DNA

  9. Exons DNA RNA transcript or RNA splicing Figure 11.7 mRNA 0 • 11.7 Eukaryotic RNA may be spliced in more than one way • After transcription, alternative splicing • May generate two or more types of mRNA from the same transcript

  10. RNAi – RNA Interference

  11. 0 • 11.8 Translation and later stages of gene expression are also subject to regulation • Once in the Cytoplasm: • mRNA breakdown • Post-translational modification by cleavage, or addition of functional groups like phosphate

  12. SH Folding of polypeptide andformation of S—S linkages SH S S S Cleavage S S S SH SH S SH S SH S S S S Initial polypeptide(inactive) Folded polypeptide(inactive) Active formof insulin Figure 11.8 0 • Protein Activation • Polypeptides may require alteration to become functional

  13. 0 • Protein Breakdown • Some of the proteins that trigger metabolic changes in cells • Are broken down within a few minutes or hours

  14. NUCLEUS Chromosome DNA unpacking Other changes to DNA Gene Gene Transcription Exon RNA transcript Intron Addition of cap and tail Tail Splicing mRNA in nucleus Cap Flow throughnuclear envelope mRNA in cytoplasm CYTOPLASM Breakdown of mRNA Broken-downmRNA Translation Polypeptide Cleavage / modification / activation Active protein Breakdownof protein Broken-downprotein Figure 11.9 0 • 11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes

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