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Chapter 11 How Genes Are Controlled PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko Introduction Cloning is the creation of an individual by asexual reproduction. The ability to clone an animal from a single cell demonstrates that every adult body cell – contains a complete genome that is – capable of directing the production of all the cell types in an organism. © 2012 Pearson Education, Inc. Introduction Cloning has been attempted to save endangered species. However, cloning – does not increase genetic diversity and – may trivialize the tragedy of extinction and detract from efforts to preserve natural habitats. © 2012 Pearson Education, Inc. Figure 11.0_1 Chapter 11: Big Ideas Control of Gene Expression The Genetic Basis of Cancer Cloning of Plants and Animals Figure 11.0_2 CONTROL OF GENE EXPRESSION © 2012 Pearson Education, Inc. Prokaryotes turn genes on or off in response to environmental changes Gene regulation is the turning on and off of genes. Gene expression is the overall process of information flow from genes to proteins. The control of gene expression allows cells to produce specific kinds of proteins when and where they are needed. Our earlier understanding of gene control came from the study of E. coli. © 2012 Pearson Education, Inc. Figure 11.1A E. coli Prokaryotes turn genes on or off in response to environmental changes A cluster of genes with related functions, along with the control sequences, is called an operon. With few exceptions, operons only exist in prokaryotes. © 2012 Pearson Education, Inc. Parts of An Operon Structural genes: genes under the control of the operon Promoter: DNA sequence where RNA polymerase binds and initiates transcription of structural genes Operator: DNA sequence where a repressor can bind and block RNA polymerase action. Repressor: Protein that binds operator sequence and blacks RNA polymerase Regulator gene: gene that codes for repressor protein A typical operon Regulatory gene Promoter Operator Gene 1 Gene 2 Gene 3 DNA Encodes a repressor that in active form attaches to an operator © 2012 Pearson Education, Inc. RNA polymerase binding site Switches the operon on or off Code for proteins The lac operon When an E. coli encounters lactose, all the enzymes needed for its metabolism are made at once using the lactose operon. – In the absence of lactose, the repressor binds to the operator and prevents RNA polymerase action. – In presence of lactose, lactose inactivates the repressor, so – the operator is unblocked, – RNA polymerase can bind to the promoter, and – all three genes of the operon are transcribed. © 2012 Pearson Education, Inc. The lac Operon of E. coli Figure 11.1B Operon turned off (lactose is absent): OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA RNA polymerase cannot attach to the promoter mRNA Protein Active repressor Operon turned on (lactose inactivates the repressor): DNA RNA polymerase is bound to the promoter mRNA Translation Protein Lactose Inactive repressor Enzymes for lactose utilization The lac Operon The lac Operon The trp operon Allows bacteria to produce tryptophan in the absence of this amino acid in environment. Absence of Tryptophan ACTIVATES trp operon. There are two types of repressor-controlled operons. – In the lac operon, the repressor is – active when alone and – inactive when bound to lactose. – In the trp bacterial operon, the repressor is – inactive when alone and – active when bound to the amino acid tryptophan (Trp). © 2012 Pearson Education, Inc. Figure 11.1C trp operon lac operon Promoter Operator Gene DNA Active repressor Active repressor Inactive repressor Lactose Inactive repressor Tryptophan The trp Operon: The trp Operon: The trp Operon: