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Why genes are regulated Organisms respond to environment - e.g. nutrients available Multi-cellular organisms must have different cell types (differentiation)

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Presentation on theme: "Why genes are regulated Organisms respond to environment - e.g. nutrients available Multi-cellular organisms must have different cell types (differentiation)"— Presentation transcript:

1 Why genes are regulated Organisms respond to environment - e.g. nutrients available Multi-cellular organisms must have different cell types (differentiation) Genes must be switched on/off at correct times and in correct cells Gene regulation is complex and precisely controlled process

2 DNA does not change All cells in an organism have the same set of genes (usually) DNA sequence does not change but genes can be switched on/off Gene regulation must be a reversible process Some gene activities are required in all cell types (housekeeping genes) e.g. synthesis of RNA Others are tissue specific e.g. to make muscle proteins (myosin, actin) in muscle cells

3 Any cell has all genes to make frog Unfertilised egg Destroy nucleus by UV light Normal tadpole Normal embryo Adult frog Skin cell removed and cultured Nucleus removed and micro-injected into egg

4 Regulation at what stage? Several places at which regulation could occur Mostly regulated at transcription stage Most economical - dont make things that arent needed Achieved by specific proteins that bind to DNA DNARNAProtein Transport, Processing transcriptiontranslation Active protein

5 DNA binding proteins Specific proteins bind to specific points in the DNA The two fit together like a lock and key Almost all genes are regulated this way DNAProtein

6 Gene regulation in bacteria Simple systems to turn genes on and off Response to nutrients e.g. if tryptophan (an amino acid) is in the medium, dont need to make your own Similar systems exist for other amino acids Turning a gene off is repression

7 Tryptophan (trp) gene regulation promoter E D C B A trp synthesis enzymes DNA RNA No trp Trp present Repressor protein RNA polymerase No transcription Trp operon

8 Gene activation Bacteria turn on genes to use sugars for energy when available Turning genes on is activation Also uses specific DNA-binding proteins protein DNA RNA RNA polymerase Activator protein Environmental stimulus Promoter

9 Gene regulation in eukaryotes Genes have to be switched on by regulatory proteins, otherwise would do nothing General proteins in all cell types, special ones in specific cell types Regulatory proteins bind to sites in DNA called enhancers Enhancers can be 1000s of bp away from gene

10 Gene regulation in eukaryotes Specific activator protein Enhancer Promoter RNA polymerase & general transcription factors

11 Drosophila eye development Cells for eyeCells for leg Larva Adult Normal Ey gene artificially expressed in cells for leg Eye on leg


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