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Unit IIIInformation Essential to Life Processes
Learning Goal 2Describe how the expression of genetic
information involves cellular and molecular mechanisms
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I. Gene regulation results in differential gene expression, leading to cell specialization.
A. Both DNA regulatory sequences, regulatory genes, and small regulatory RNAs are involved in gene expression.
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1. Regulatory sequences are stretches of DNA that interact with regulatory proteins to control transcription.
Examples are promoters, terminators, and enhancers.
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2. A regulatory gene is a sequence of DNA encoding a regulatory protein or RNA.
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B. Both positive and negative control mechanisms regulate gene expression in bacteria and viruses
1. The expression of specific genes can be turned on by the presence of an inducer.
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2. The expression of specific genes can be inhibited by the presence of a repressor.
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3. Inducers and repressors are small molecules that interact with regulatory proteins and/or regulatory sequences.
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4. Regulatory proteins inhibit gene expression by binding to DNA and blocking transcription (negative control)
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5. Regulatory proteins stimulate gene expression by binding to DNA and stimulating transcription (positive control) or binding to repressors to inactivate repressor function.
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6. Certain genes are continuously expressed; that is, they are always turned “on,” e.g., the ribosomal genes.
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C. In eukaryotes, gene expression is complex and control involves regulatory genes, regulatory elements and transcription factors that act in concert.
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2. Some of these transcription factors are activators (increase expression), while others are repressors (decrease expression).
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D. Gene regulation accounts for some of the phenotypic differences between organisms with similar genes.
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II. A variety of intercellular and intracellular signal transmissions mediate gene expression.
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A. Signal transmission within and between cells mediates gene expression.
Examples:Cytokines regulate gene expression to allow for cell replication and division.
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Mating pheromones in yeast trigger gene expression.
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Levels of cAMP regulate metabolic gene expression in bacteria.
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Expression of the SRY gene triggers the male sexual development pathway in animals.
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Ethylene levels cause changes in the production of different enzymes, allowing fruits to ripen.
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Seed germination and gibberellin.
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B. Signal transmission within and between cells mediates cell function.Examples:Morphogens stimulate cell differentiation and development.
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Changes in p53 activity can result in cancer.
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HOX genes and their role in development.
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http://www.youtube.com/watch?v=3S3ZOmleAj0&feature=player_detailpage