ch 11 for 2009_Lectures_PPT - jgb

ch 11 for 2009_Lectures_PPT - jgb - BIOL 100 General...

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1 BIOL 100 – General Biology JG Boal Chapter 11 – The Control of Gene Expression
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2 DNA molecule Gene 1 Gene 2 Gene 3 A A A A A C C G G C C C G G G U U U U U U U A A DNA strand Transcription RNA Translation Polypeptide Amino acid Codon Review
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3 Questions for Today: We know all cells produced through mitosis have the same genetic information . How can a cell respond to particular events? How is it that cells become specialized, such as when some cells become bone and other cells become muscle? How does a organism develop from a fertilized egg and then stop developing? If we know how these transformations happen, can we use this information to help people?
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4 Gene regulation is the "turning on" and "turning off" of genes Helps organisms respond to environmental changes Gene regulation controls gene expression Gene expression is the process by which information flows from genes to protein
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5 Early understanding of gene control came from studies of the bacterium Escherichia coli Prokaryotes :
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6 Organisms only make what they need – minimize waste (energy, resources) How are genes regulated (turned on and off)?
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7 An operon is a cluster of genes with related functions. It includes promoter : the start sequence where the RNA polymerase binds operator : the switch (on/off) for the binding of RNA polymerase the genes that are needed for the particular functions Promoter Operator Lactose-utilization genes OPERON start switch genes for function
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8 A repressor binds to the operator (switch), stopping transcription A regulatory gene , located outside the operon , codes for the repressor
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9 Example 1: Suppose a bacterium is surrounded by milk. It needs to turn on the genes to make enzymes to digest the milk.
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10 Regulatory gene Promoter Operator Lactose-utilization genes OPERON DNA mRNA Protein Operon turned off (lactose absent) DNA mRNA RNA polymerase bound to promoter Active repressor RNA polymerase cannot attach to promoter Protein Lactose Inactive repressor Enzymes for lactose utilization Operon turned on (lactose inactivates repressor) No milk: Milk: lac (lactose) operon
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11 Example 2: Tryptophan is an amino acid essential to building proteins. Bacteria can make tryptophan, and usually do. But if there is tryptophan in the environment, it is better to just take it from the environment, rather than build it. The trp operon works in the opposite way from the lac operon .
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12 Suppose a bacterium is surrounded by tryptophan. It needs to turn off the genes that code for building tryptophan.
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13 The trp operon allows bacteria to stop making tryptophan when it is already present Repressor is inactive alone – cell builds tryptophan If tryptophan in the environment, it binds to the repressor and activates it – cell stops building tryptophan
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14 LE 11-1c Inactive repressor Active repressor Tryptophan Genes trp operon trp operon
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15 LE 11-1c DNA Active repressor Inactive repressor lac operon Lactose Inactive repressor Active repressor Tryptophan Promoter Operator Genes trp operon lac operon trp operon
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This note was uploaded on 05/04/2011 for the course ECON 222 taught by Professor Jeffery during the Spring '11 term at E. Stroudsburg.

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ch 11 for 2009_Lectures_PPT - jgb - BIOL 100 General...

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