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Gene Regulation

Gene Regulation. Structure and Function = Genetic Information + EXPRESSION of info! Ch’s 18 & 19 (347-372). Review (RNA synthesis - pgs 309-313). Define: Promoter – Terminator – TATA Box – Intron – Exon –. Expression of genetic information controls: Cell Products Metabolism

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Gene Regulation

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  1. Gene Regulation Structure and Function = Genetic Information + EXPRESSION of info! Ch’s 18 & 19 (347-372)

  2. Review(RNA synthesis - pgs 309-313) Define: Promoter – Terminator – TATA Box – Intron – Exon –

  3. Expression of genetic information controls: • Cell Products • Metabolism • Nature (type) of the Cell Why not always express? • Energy efficiency and thus increased metabolism (metabolic fitness)

  4. Control of Gene Expression • Environmental Signals • Developmental Cascades • Regulatory Genes • Structural Genes • Regulatory Systems • Inducible and Repressible (Operons) in bacteria • Pathways with positive and negative regulatory motifs • Regulatory Molecules (Eukaryotes)

  5. Gene Regulation DNA Regulatory Sequences – stretches of DNA that interact with regulatory proteins to control transcription • Promoters – DNA sequence that binds with RNA polymerase, starts transcription • Terminators – DNA sequence that ends transcription, RNA poly. releases new mRNA • Enhancers – DNA sequence that recognizes transcription factors that start transcription on other genes

  6. Gene Regulation Regulatory Gene – sequence of DNA encoding a regulatory protein that controls the transcription of another gene or genes

  7. Prokaryotes

  8. Prokaryotic Gene Regulation • Metabolism of bacteria varies in response to what it eats  can vary amount of enzymes made AND activity of enzymes present • Allows them to adapt to short term fluctuations in available needed substances • Control of enzyme (remember… they are PROTEINS) production occurs during transcription

  9. “the operon model” Three Parts: • Promoter – where RNA polymerase attaches • Operator – “on/off”switch, controls access of RNA polymerase to genes • Genes – code for related enzymes in a pathway

  10. Positive and negative control mechanisms. Small molecules involved: • Expression turned on by presence of INDUCER • Expression inhibited by the presence of a REPRESSOR

  11. NEGATIVE CONTROL – When regulatory proteins inhibit gene expression by binding to DNA and blocking transcription • POSITIVE CONTROL – When regulatory proteins start gene expression by binding to DNA and stimulating transcription • Certain genes are continuously expressed… (always turned on – ex. ribosomal genes)

  12. Positive Control Mechanisms Example: Cyclic AMP (cAMP) – molecule that accumulates when glucose is scarce (the inducer) cAMP Receptor Protein (CRP) – protein that activates transcription when cAMP binds to its allosteric site • DNA is ‘bent,’ making it easier for RNA polymerase to bind the promoter and start transcription

  13. Negative Control Mechanisms trpoperon – a repressible operon (inhibited by tryptophan- a repressor molecule) • Normally ON • Anabolic (build organic molecules) • Organic molecule product acts as corepressor binds to repressor to activate it • Operon is turned OFF – RNA polymerase can not attach to the promoter TRYPTOPHAN

  14. Negative Control Mechanisms lac operon – an inducible operon (stimulated by lactose – an inducer molecule) • Normally OFF • Catabolic (break down food for energy) • Repressor is active inducerbinds to and inactivates repressor • Operon is turned ON LACTOSE

  15. Eukaryotic Gene Regulation

  16. Same DNA… So why different types of cells?

  17. Differential expression of GENES results in Cell Specialization (different types of cells)! Genes are expressed (turned on or off) at different points of protein synthesis: • During Transcription • Exons vs Introns that are selected • What mRNA gets transported out of the nucleus • Modification of protein shapes (changes their functions)

  18. Chromatin Structure  Influences Transcription

  19. Chromatin Structure • EUCHROMATIN - Loosely packed – RNA polymerase can read it (YES expression) • HETEROCHROMATIN – Tightly packed (NO expression) OR: • Acetylation of histones– loosens chromatin structure (MORE transcription) • DNA Methylation – add methyl groups to pack DNA tightly together  harder to transcribe (LESS transcription)

  20. How does the cell know which genes to transcribe? Transcription Factors (TF’s) • Made by regulatory genes • Help RNA Polymerase bind to certain DNA regions called PROMOTERS = Activators  DNA upstream of promoters FOLDS back on itself and activates RNA polymerase to make mRNA (make the “gene”) • Some TF’s are Repressors (inhibit RNA polymerase)

  21. So… what activates Transcription Factors (TF’s)? • Signals are transmitted by various molecules in various ways that activate transcription factors • Gene expression and cell function is mediated by signal transmission. Examples: • Cytokines: allow cell cycle to go forth (allow cells to go forward and divide) • SRY gene – on “Y” chromosome – activation of TF’s promotes male sexual development pathway in animals

  22. What happens when gene expression goes wrong? Proto-oncogenes – genes that code for proteins that stimulate normal cell growth and division ex: rasgene Oncogene – cancer causing gene Mutations can cause a Proto-onco gene to change into an oncogene = stimulates many TF’s which stimulates cells to divide  cancer (uncontrolled cell division)

  23. Other cancer regulators Tumor-Suppressor Protein – a TF that promotes synthesis of the cell cycle- INHIBITING proteins EX: p53 gene (“guardian angel of the genome”)  No p53, no inhibition of excess cell growth = CANCER

  24. HOX (Homeotic) Genes • Genes important in embryo development in all Domains! • Contain DNA sequence with a homeobox • Code for specific segments of bodies • Highly conserved (present) through many organisms! Identical sequences found in many organisms…

  25. HOX genes in various organisms

  26. Evolution Connection • Gene sequences evolve and are conserved across species • Errors (or changes) in regulation of genes involves in development led to sever, detrimental, or bizarreconsequences.

  27. Phenotypic Differences • Gene regulation (thus protein activity) accounts for differences between organisms with similar genes. • Enzymatic reactions • Transport by proteins • Synthesis of structures, chemicals, etc. • Degradation of waste products, etc. • Genetic engineering techniques can manipulate the heritable info of DNA (and sometimes RNA) • Electrophoresis • Plasmid-based transformation • Restriction enzyme analysis of DNA • Polymerase Chain Reaction

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