Prokaryotes and eukaryotes alter gene expression in response to their changing environment

Transcription

1 Chapter 18

2 Prokaryotes and eukaryotes alter gene expression in response to their changing environment In multicellular eukaryotes, gene expression regulates development and is responsible for differences in cell types RNA molecules play many roles in regulating gene expression in eukaryotes

3 Natural selection has favored bacteria that produce only the products needed by that cell A cell can regulate the production of enzymes by feedback inhibition or by gene regulation Gene expression in bacteria is controlled by the operon model

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5 Operon: 6 min AS cluster of related genes with on/off switch Three Parts Bozeman 10 min: 1. Promoter where RNA polymerase attaches 2. Operator on/off, controls access of RNA poly 3. Genes code for related enzymes in a pathway

6 Regulatory gene: produces repressor protein that binds to operator to block RNA poly

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8 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

9 trp operon

10 Normally OFF Catabolic (break down food for energy) Repressor is active inducer binds to and inactivates repressor Operon is turned ON Eg. lac operon

11 lac operon

12 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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14 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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16 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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18 Transcription Initiation: Control elements bind transcription factors Enhances gene expression

19 Enhancer regions bound to promoter region by activators

20 Only a small fraction of DNA codes for proteins, rrna, and trna A significant amount of the genome may be transcribed into noncoding RNAs Noncoding RNAs regulate gene expression at two points: mrna translation and chromatin configuration

21 Regulation of mrna: micro RNAs (mirnas) and small interfering RNAs (sirnas= RNAi) can bind to mrna and degrade it or block translation

22 MicroRNAs (mirnas) are small singlestranded RNA molecules that can bind to mrna These can degrade mrna or block its translation

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24 The phenomenon of inhibition of gene expression by RNA molecules is called RNA interference (RNAi) RNAi is caused by small interfering RNAs (sirnas) sirnas and mirnas are similar but form from different RNA precursors

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27 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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29 Cytoplasmic determinants: maternal substances in egg distributed unevenly in early cells of embryo

30 Induction: cells triggered to differentiate Cell-Cell Signals: molecules produced by one cell influences neighboring cells Eg. Growth factors

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35 1. Proto-oncogene = stimulates cell division 2. Tumor-suppressor gene = inhibits cell division Mutations in these genes can lead to cancer

36 Proto-Oncogene Gene that stimulates normal cell growth & division Oncogene Mutation in protooncogene Cancer-causing gene Effects: Increase product of proto-oncogene Increase activity of each protein molecule produced by gene

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38 Ras gene: stimulates cell cycle (protooncogene) 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

39 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

40 Embryonic development occurs when gene regulation proceeds correctly Cancer occurs when gene regulation goes awry