© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 11 How Genes Are Controlled

 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. Introduction © 2012 Pearson Education, Inc.

 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. Introduction © 2012 Pearson Education, Inc.

Figure 11.0_1 Chapter 11: Big Ideas Control of Gene Expression Cloning of Plants and Animals The Genetic Basis of Cancer

Figure 11.0_2

CONTROL OF GENE EXPRESSION © 2012 Pearson Education, Inc.

 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. Prokaryotes turn genes on or off in response to environmental changes © 2012 Pearson Education, Inc.

Figure 11.1A E. coli

 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. Prokaryotes turn genes on or off in response to environmental changes

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 © 2012 Pearson Education, Inc. A typical operon DNA Regulatory gene Promoter Operator Gene 1 Gene 2 Gene 3 Encodes a repressor that in active form attaches to an operator 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 RNA polymerase cannot attach to the promoter Active repressor Protein mRNA DNA Protein mRNA DNA Operon turned on (lactose inactivates the repressor): RNA polymerase is bound to the promoter Lactose Inactive repressor Translation Enzymes for lactose utilization

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 Inactive repressor Active repressor Lactose Tryptophan DNA Promoter Operator Gene lac operon trp operon

The trp Operon: