Chapter 17 Regulation of gene expression in bacteria: lac Operon of E. coli trp operon of E. coli.
Ch. 18 Warm-Up -...
Transcript of Ch. 18 Warm-Up -...
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Chapter 18
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Transcription
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Operon: cluster of related genes with on/off switch
Three Parts:
1. Promoter – where RNA polymerase attaches
2. Operator – “on/off”, controls access of RNA poly
3. Genes – code for related enzymes in a pathway
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Regulatory gene: produces repressor protein that binds to operator to block RNA poly
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Normally ON
Anabolic (build organic molecules)
Organic molecule product acts as corepressor binds to repressor to activate it
Operon is turned OFF
Eg. trp operon
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trp operon
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Normally OFF
Catabolic (break down food for energy)
Repressor is active inducer binds to and inactivates repressor
Operon is turned ON
Eg. lac operon
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lac operon
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Many stages
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Typical human cell: only 20% of genes expressed at any given time
Different cell types (with identical genomes) turn on different genes to carry out specific functions
Differences between cell types is due to differential gene expression
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Chromatin Structure:
Tightly bound DNA less accessible for transcription
DNA methylation: methyl groups added to DNA; tightly packed; transcription
Histone acetylation: acetyl groups added to
histones; loosened; transcription
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Modifications on chromatin can be passed on to future generations
Unlike DNA mutations, these changes to chromatin can be reversed (de-methylation of DNA)
Explains differences between identical twins
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Transcription Initiation:
Control elements bind transcription factors
Enhances gene expression
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Enhancer regions bound to promoter region by activators
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Regulation of mRNA:
• micro RNAs (miRNAs) and small interfering RNAs (siRNAs) can bind to mRNA and degrade it or block translation
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Section 18.4
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1. Cell Division: large # identical cells through mitosis
2. Cell Differentiation: cells become specialized in structure & function
3. Morphogenesis: “creation of form” – organism’s shape
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Cytoplasmic determinants: maternal substances in egg distributed unevenly in early cells of embryo
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Induction: cells triggered to differentiate
Cell-Cell Signals: molecules produced by one cell influences neighboring cells ◦ Eg. Growth factors
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Section 18.5
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1. Proto-oncogene = stimulates cell division
2. Tumor-suppressor gene = inhibits cell division
Mutations in these genes can lead to cancer
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Proto-Oncogene Oncogene
Gene that stimulates normal cell growth & division
Mutation in proto-oncogene
Cancer-causing gene Effects: Increase product of
proto-oncogene Increase activity of
each protein molecule produced by gene
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Ras gene: stimulates cell cycle (proto-oncogene)
◦ Mutations of ras occurs in 30% of cancers
p53 gene: tumor-suppresor gene
◦ Functions: halt cell cycle for DNA repair, turn on DNA repair, activate apoptosis (cell death)
◦ Mutations of p53 in 50+% of cancers
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Cancer results when mutations accumulate (5-7 changes in DNA)
Active oncogenes + loss of tumor-suppressor genes
The longer we live, the more likely that cancer might develop
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Embryonic development occurs when gene regulation proceeds correctly
Cancer occurs when gene regulation goes awry