Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Epitranscriptome wikipedia , lookup
Transcription factor wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Gene regulatory network wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
RNA polymerase II holoenzyme wikipedia , lookup
Histone acetylation and deacetylation wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Gene expression wikipedia , lookup
Chapter 18 Regulation of Gene Expression PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Bacterial Genome and Its Replication • Bacterial chromosome – Circular DNA molecule – Few associated proteins • Binary Fission Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 18-14 Replication fork Origin of replication Termination of replication Concept 18.4: Individual bacteria respond to environmental change by regulating their gene expression • Bacterial metabolism can change with changing environment and food sources • Metabolic control on two levels: – Adjusting activity of metabolic enzymes – Regulating genes that encode metabolic enzymes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bacterial Genome: Operons: • Genes clustered into Operons – Promoter – Operator = “on-off” switch – Genes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bacterial Genome: Operons: • Genes clustered into Operons – Operator = “on-off” switch – Promoter – Genes • Repressor- Protein that can switch off Operator • Inducer- Small molecule that cooperates with a repressor to switch an Operon off Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lac operon = inducible (usually OFF) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Repressible vs. Inducible Operons • Inducible operon = usually off • Inducer inactivates the repressor turns on transcription • Ex: lac operon Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Repressible vs. Inducible Operons • Inducible operon = usually off • Inducer inactivates the repressor turns on transcription • Ex: lac operon • Repressible operon = usually on • binding of a repressor to the operator shuts off transcription • Ex: trp operon Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Chromatin = DNA + proteins – Euchromatin- chromatin in non-condensed state (~packaging level 2) – Heterochromatin- chromatin in highly condensed state (always packaging level 4) • What DNA would be found in this state? – Skin vs. Nerve cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 19.2: Regulation of gene expression • Each cell type expresses only a fraction of its genes (skin vs. muscle cells) • All organisms regulate which genes are expressed HOW? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Gene expression: 1. Chromatin structure 2. Transcription initiation 3. Post-transcriptional/translational (mRNA or polypeptide) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. Chromatin Structure: Histone Modification • Chemical modification of histone tails: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Histone acetylation- Add acetyl group (-COCH3) Positive charge of histone neutralized Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Histone acetylation- Add acetyl group (-COCH3) Positive charge of histone neutralized Loosen chromatin structure transcription Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • DNA Methylation • Add methyl groups (-CH3) to certain DNA bases • = Condenses chromatin • EX: Inactivated X chromosome in females Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Gene expression: 1. Chromatin structure 2. Transcription initiation 3. Post-transcriptional/translational (mRNA or polypeptide) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. Regulation of Transcription Initiation • Control elements –non-coding DNA, bind proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Enhancers and Specific Transcription Factors • Proximal control elements = close to the promoter • Distal control elements = enhancers – May be far away from a gene or even in an intron Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • To initiate transcription – Eukaryotic RNA polymerase requires the assistance of transcription factors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • To initiate transcription – Eukaryotic RNA polymerase requires the assistance of transcription factors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • An activator = protein that binds to an enhancer and stimulates transcription of a gene Figure 19.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings #1 #2 1. Activators bind to enhancer 2. DNA bending protein, mediator proteins and Transcription factors recruited Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings #1 3. Transcription factors and mediator proteins bind to activators #2 -Transcription factors bind to promoter #3 -RNA polymerase binds to promoter Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Repressors = Inhibit expression of a gene Repressors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Gene expression: • Chromatin structure • Transcription initiation • Post-transcriptional (mRNA) Post-translational (polypeptide) Modifications Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 3. Post-transcriptional modification: • “After transcription” Splicing Figure 19.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Post-Transcriptional: mRNA Degradation • Life span of mRNA molecules short Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Post-Translational modifications: • “After translation” – Cleavage of certain a.a. – Addition of chemical groups Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Post-translational: Proteasomes – Giant protein complexes that bind protein molecules and degrade them 3 Enzymatic components of the 1 Multiple ubiquitin molecules are attached to a protein by enzymes in the cytosol. 2 The ubiquitin-tagged protein is recognized by a proteasome, which unfolds the protein and sequesters it within a central cavity. Figure 19.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings proteasome cut the protein into small peptides, which can be further degraded by other enzymes in the cytosol. • Ch. 18 Bacterial genomes • Basic replication • Lac Operon Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings