Gene regulation eukaryotes
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Controlling gene expression in eukaryotic cells
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Gene regulation eukaryotes
- 2. Control Of Expression In Eukaryotes Some of the general methods used to control expression in prokaryotes are used in eukaryotes, but nothing resembling operons is known Eukaryotic genes are controlled individually and each gene has specific control sequences preceding the transcription start site In addition to controlling transcription, there are additional ways in which expression can be controlled in eukaryotes
- 3. Eukaryotes Have Large Complex Geneomes The human genome is about 3 x 109 base pairs or ≈ 1 m of DNA Because humans are diploid, each nucleus contains 6 3 x 109 base pairs or ≈ 2 m of DNA That is a lot to pack into a little nucleus!
- 4. Only a Subset of Genes is Expressed at any Given Time It takes lots of energy to express genes Thus it would be wasteful to express all genes all the time By differential expression of genes, cells can respond to changes in the environment Differential expression, allows cells to specialize in multicelled organisms. Differential expression also allows organisms to develop over time.
- 5. DNA Cytoplasm Nucleus G AAAAAA Export Degradation etc. G AAAAAA Control of Gene Expression G AAAAAA RNA Processing mRNA RNA Transcription Nuclear pores Ribosome Translation Packaging Modification Transportation Degradation
- 6. Logical Expression Control Points DNA packaging Transcription RNA processing mRNA Export mRNA masking/unmasking and/or modification mRNA degradation Translation Protein modification Protein transport Protein degradation Increasingcost The logical place to control expression is before the gene is transcribe d
- 7. Eukaryotic DNA Must be Packaged Eukaryotic DNA exhibits many levels of packaging The fundamental unit is the nucleosome, DNA wound around histone proteins Nucleosomes arrange themselves together to form higher and higher levels of packaging.
- 8. Packaging DNAPackaging DNA G C A T Protein scaffold Metaphase Chromosome Looped Domains Nucleosomes B DNA Helix Tight helical fiber
- 9. Highly Packaged DNA Cannot be Expressed The most highly packaged form of DNA is “heterochromatin” Heterochromatin cannot be transcribed, therefore expression of genes is prevented Chromosome puffs on some insect chomosomes illustrate where active gene expression is going on
- 10. Eukaryotic RNA Polymerase II RNA polymerase is a very fancy enzyme that does many tasks in conjunction with other proteins RNA polymerase II is a protein complex of over 500 kD with more than 10 subunits:
- 11. Eukaryotic RNA Polymerase II Promoters Several sequence elements spread over about 200 bp upstream from the transcription start site make up RNA Pol II promoters Enhancers, in addition to promoters, influence the expression of genes Eukaryotic expression control involves many more factors than control in prokaryotes This allows much finer control of gene expression
- 12. RNA Pol. II Initiation T. F. RNA Pol. II 5’ mRNA Promoter T. F. T. F.
- 13. Eukaryotic RNA Polymerase II Promoters Eukaryotic promoters are made up of a number of sequence elements spread over about 200 bp upstream from the transcription start site In addition to promoters, enhancers also influence the expression of genes Control of gene expression in eukaryotes involves many more factors than control in prokaryotes This allows much finer control of gene expression
- 14. A “Simple” Eukaryotic Gene Terminator Sequence Promoter/ Control Region Transcription Start Site 3’5’ RNA Transcript Introns Exon 2 Exon 3Int. 2Exon 1 Int. 1 3’ Untranslated Region 5’ Untranslated Region Exons
- 15. Eukaryotic Promoters 5’ Exon 1Promoter Sequence elements ~200 bp TATA ~-25 Initiator“TATA Box” Transcription start site (Template strand) -1+1 SSTATAAAASSSSSNNNNNNNNNNNNNNNNNYYCAYYYYYNN S = C or G Y = C or T N = A, T, G or C
- 16. Response Elements Response elements are short sequences found either within about 200 bp of the transcription start site, or as part of enhancers Different genes have different response elements Binding of transcription factors to response elements determines which genes will be expressed in any cell type under any set of conditions
- 17. Initiation TFIID Binding -1+1 Transcription start site TFIID “TATA Box” TBP Associated Factors (TAFs) TATA Binding Protein (TBP)
- 19. Initiation TFIIA and B Binding TFIID TFIIA -1+1 Transcription start site TFIIB
- 20. Initiation TFIIF and RNA Polymerase Binding TFIID TFIIA -1+1 Transcription start site TFIIB RNA Polymerase TFIIF
- 21. Initiation TFIIE Binding TFIID TFIIA -1+1 Transcription start site RNA Polymerase TFIIBTFIIF TFIIE TFIIE has some helicase activity and may by involved in unwinding DNA so that transcription can start
- 22. Initiation TFIIH and TFIIJ Binding TFIID TFIIA -1+1 Transcription start site RNA Polymerase TFIIBTFIIF TFIIE TFIIH has some helicase activity and may by involved in unwinding DNA so that transcription can start TFIIH P P P TFIIJ
- 23. Initiation TFIIH and TFIIJ Binding TFIID TFIIA -1+1 Transcription start site RNA Polymerase TFIIBTFIIF TFIIE TFIIH P P P TFIIJ
- 24. Initiation TFIIH and TFIIJ Binding -1+1 Transcription start site RNA Polymerase P P P
- 25. 5’ DNA 3’ Enhancers Enhancer Transcribed Region 3’5’ TF TF TF 3’5’ TF TF TF 5’ RNA RNA Pol. RNA Pol. Many bases Promoter