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Chapter 11 Gene Expression Table of Contents Section 1 Control of Gene Expression Section 2 Gene Expression in Development and Cell Division Chapter 11 Section 1 Control of Gene Expression Objectives • Explain why cells regulate gene expression. • Discuss the role of operons in prokaryotic gene expression. • Determine how repressor proteins and inducers affect transcription in prokaryotes. • Describe the structure of a eukaryotic gene. • Compare the two ways gene expression is controlled in eukaryotes. Chapter 11 Gene Expression Standards: • SPI 3210.4.8 Determine the relationship between mutations and human genetic disorders. • SPI 3210.4.9 Evaluate the scientific and ethical issues associated with gene technologies: genetic engineering, cloning, transgenic organism production, stem cell research, and DNA fingerprinting. Chapter 11 Section 1 Control of Gene Expression Role of Gene Expression • Gene expression is the activation of a gene that results in transcription and the production of mRNA. • Only a fraction of any cell’s genes are expressed at any one time. Chapter 11 Section 1 Control of Gene Expression Gene Expression in Prokaryotes • An operon is a series of genes that code for specific products and the regulatory elements that control these genes. In prokaryotes, the structural genes, the promoter, and the operator collectively form an operon. Chapter 11 Section 1 Control of Gene Expression Operon Click below to watch the Visual Concept. Chapter 11 Section 1 Control of Gene Expression Gene Expression in Prokaryotes, continued • A promoter is the segment of DNA that is recognized by the enzyme RNA polymerase, which then initiates transcription. • An operator is the segment of DNA that acts as a “switch” by controlling the access of RNA polymerase to the promoter. Chapter 11 Section 1 Control of Gene Expression Gene Expression in Prokaryotes, continued • Operon “Turned Off” – Repressor proteins are coded for by regulator genes and these proteins inhibit genes from being expressed. – A repressor protein attaches to the operator, physically blocking the advancement of RNA polymerase. Chapter 11 Section 1 Control of Gene Expression Repression of Transcription in the lac Operon Click below to watch the Visual Concept. Chapter 11 Section 1 Control of Gene Expression Gene Expression in Prokaryotes, continued • Operon “Turned On” – An inducer is a molecule that initiates gene expression. In E. coli, lactose serves as an inducer. – An inducer binds to the repressor protein and the repressor protein detaches from the operator. RNA polymerase can then advance to the structural genes. Chapter 11 Section 1 Control of Gene Expression Activation of Transcription in the lac Operon Chapter 11 Section 1 Control of Gene Expression Mechanism of lac Operon Chapter 11 Section 1 Control of Gene Expression Gene Expression in Eukaryotes • Structure of a Eukaryotic Gene – Eukaryotes do not have operons. – The genomes of eukaryotes are larger and more complex than those of prokaryotes. – Eukaryotic genes are organized into noncoding sections, called introns, and coding sections, called exons. Chapter 11 Section 1 Control of Gene Expression Gene Expression in Eukaryotes, continued • Control After Transcription – In eukaryotes, gene expression can be controlled after transcription—through the removal of introns from pre-mRNA. Chapter 11 Section 1 Control of Gene Expression Removal of Introns After Transcription Chapter 11 Section 1 Control of Gene Expression Gene Expression in Eukaryotes, continued • Control at the Onset of Transcription – In eukaryotes, gene expression can be controlled at the onset of transcription—through the action of regulatory proteins known as transcription factors. Chapter 11 Section 1 Control of Gene Expression Enhancers for Control of Gene Expression Click below to watch the Visual Concept. Chapter 11 Section 1 Control of Gene Expression Controlling Transcription in Eukaryotes Chapter 11 Section 2 Gene Expression in Development and Cell Division Objectives • Summarize the role of gene expression in an organism’s development. • Describe the influence of homeotic genes in eukaryotic development. • State the role of the homeobox in eukaryotic development. • Summarize the effects of mutations in causing cancer. • Compare the characteristics of cancer cells with those of normal cells. Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression in Development • The development of cells with specialized functions is called cell differentiation. • The development of form in an organism is called morphogenesis. • Both cell differentiation and morphogenesis are governed by gene expression. Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression in Development, continued • Homeotic Genes – Homeotic genes are regulatory genes that determine where anatomical structures will be placed during development. Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression in Development, continued • Homeobox Sequences – Within each homeotic gene, a specific DNA sequence known as the homeobox regulates patterns of development. – The homeoboxes of many eukaryotic organisms appear to be very similar. Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression in Development, continued • Tracking Changes in Gene Expression – In the 1990s, researchers developed a tool for tracking gene expression called a DNA chip. Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression, Cell Division, and Cancer • Mutations of proto-oncogenes, which regulate cell growth, or tumor-suppressor genes, which prevent cell division from occurring too often,may lead to cancer. • Cancer is the uncontrolled growth of abnormal cells. Chapter 11 Section 2 Gene Expression in Development and Cell Division Effect of Mutation on Gene Expression Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression, Cell Division, and Cancer, continued • Gene Expression in Cancer – Unlike normal cells, cancer cells continue to divide indefinitely, even if they become densely packed. – Cancer cells will also continue dividing even if they are no longer attached to other cells. Chapter 11 Section 2 Gene Expression in Development and Cell Division Gene Expression, Cell Division, and Cancer, continued • Causes of Cancer – A carcinogen is any substance that can induce or promote cancer. – Most carcinogens are mutagens, substances that cause mutations.