Chapter 11 Objectives Section 1 Control of Gene Expression 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.

Role of Gene Expression Section 1 Control of Gene Expression Chapter 11 Role of Gene Expression Gene expression is the activation of a gene that results in transcription and the production of mRNA. Cells control gene expression so that their genes will only be expressed when needed Cells control the expression of their genes: With regulatory sites found on each genes With specific regulatory proteins By determining when individual genes are to be transcribed

Gene Expression in Prokaryotes, continued Section 1 Control of Gene Expression Chapter 11 Gene Expression in Prokaryotes, continued A promoter is the segment of DNA that is recognized by the enzyme RNA polymerase, which then initiates transcription. In order for RNA polymerase to attach to a DNA molecule, the RNA polymerase must recognize a promoter An operator is the segment of DNA that acts as a “switch” by regulating the access of RNA polymerase to the structural genes

Gene Expression in Prokaryotes Section 1 Control of Gene Expression Chapter 11 Gene Expression in Prokaryotes An operon is a series of genes that code for functionally related proteins and the regulatory elements that control these genes. In prokaryotes, the structural genes, the promoter, and the operator collectively form an operon. lac operon -gene system whose operator gene and three structural genes control lactose metabolism in E. coli

Chapter 11 Operon Section 1 Control of Gene Expression Click below to watch the Visual Concept. Visual Concept

Gene Expression in Prokaryotes, continued Section 1 Control of Gene Expression Chapter 11 Gene Expression in Prokaryotes, continued Operon “Turned Off” (LACTOSE IS ABSENT) 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.

Repression of Transcription in the lac Operon Section 1 Control of Gene Expression Chapter 11 Repression of Transcription in the lac Operon Click below to watch the Visual Concept. Visual Concept

Gene Expression in Prokaryotes, continued Section 1 Control of Gene Expression Chapter 11 Gene Expression in Prokaryotes, continued Operon “Turned On” (LACTOSE PRESENT) 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/removes from the operator. RNA polymerase can then advance to the structural genes. Inducer molecules allow transcription to proceed by changing the shape of repressor proteins

Activation of Transcription in the lac Operon Section 1 Control of Gene Expression Chapter 11 Activation of Transcription in the lac Operon Click below to watch the Visual Concept. Visual Concept

Mechanism of lac Operon Section 1 Control of Gene Expression Chapter 11 Mechanism of lac Operon

Gene Expression in Eukaryotes Section 1 Control of Gene Expression Chapter 11 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 2 segments: Introns - noncoding sections exons - coding sections

Gene Expression in Eukaryotes, continued Section 1 Control of Gene Expression Chapter 11 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 (form of messenger RNA that contains both introns and exons)

Removal of Introns After Transcription Section 1 Control of Gene Expression Chapter 11 Removal of Introns After Transcription

Gene Expression in Eukaryotes, continued Section 1 Control of Gene Expression Chapter 11 Gene Expression in Eukaryotes, continued Control After Transcription After mRNA has been transcribed: Its introns are cut out Its exons are joined together It leaves the nucleus

Gene Expression in Eukaryotes, continued Section 1 Control of Gene Expression Chapter 11 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. Enhancer – sequence of nucleotides in a DNA molecule that aids in arranging RNA polymerase in the correct position on the promoter

Enhancers for Control of Gene Expression Section 1 Control of Gene Expression Chapter 11 Enhancers for Control of Gene Expression Click below to watch the Visual Concept. Visual Concept

Controlling Transcription in Eukaryotes Section 1 Control of Gene Expression Chapter 11 Controlling Transcription in Eukaryotes

Section 2 Gene Expression in Development and Cell Division Chapter 11 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.

Gene Expression in Development Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression in Development The development of cells with specialized functions is called cell differentiation. As organisms grow and develop, organs and tissues develop to produce a characteristic form. This development of form in an organism is called morphogenesis. Both cell differentiation and morphogenesis are governed by gene expression.

Gene Expression in Development Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression in Development Examples of Morphogenesis: The formation of cellular extensions in nerve cells and the functioning of these cells in receiving and transmitting signals The formation of long, thin muscle cells that are able to respond to the proper stimulus by contracting The formation of liver cells that produce enzymes that break down fat

Gene Expression in Development, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression in Development, continued Homeotic Genes Homeotic genes are regulatory genes that determine where anatomical structures will be placed during development.

Gene Expression in Development, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression in Development, continued Homeobox Sequences Within each homeotic gene, a specific DNA sequence known as the homeobox regulates patterns of development. Pg 224, Figure 11-5 The homeoboxes of many eukaryotic organisms appear to be very similar.

Gene Expression in Development, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression in Development, continued Characteristics of Homeoboxes They are part of genes They produce regulatory proteins that switch on or off groups of developmental genes Each controls the development of a specific part of the adult organism

Gene Expression in Development, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 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.

Gene Expression, Cell Division, and Cancer Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression, Cell Division, and Cancer Proto-oncogenes: genes that regulate the division of cells, cell growth, and ability to adhere to one another A mutation in a proto-oncogene can change the gene into a oncogene Oncogene is a gene that can cause uncontrolled cell proliferation, which can lead to CANCER

Gene Expression, Cell Division, and Cancer Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression, Cell Division, and Cancer Tumor: abnormal proliferation of cells that results from uncontrolled, abnormal cell division Benign: generally pose no threat to life Malignant: can cause cancer Cancer: uncontrolled growth of cells Tumor-suppressor genes: genes the code for proteins that prevent cell division from occurring too often Act as “brakes” to suppress tumor formation

Effect of Mutation on Gene Expression Section 2 Gene Expression in Development and Cell Division Chapter 11 Effect of Mutation on Gene Expression Mutations in proto-oncogenes or tumor-suppressor genes can destroy normal gene functioning, possibly resulting in cancer. A mutation in a proto-oncogene may cause the gene to become an oncogene, a gene that triggers cancer.

Chapter 11 Gene Expression, Cell Division, and Cancer, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 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. Metastasis: spread of malignant cells beyond their original site

Chapter 11 Gene Expression, Cell Division, and Cancer, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 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.

Chapter 11 Gene Expression, Cell Division, and Cancer, continued Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression, Cell Division, and Cancer, continued Kinds of Cancer Malignant tumors can be categorized according to the types of tissues affected Carcinomas: grow in the skin and the tissues that line the organs of the body Saracomas: grow in bone and muscle tissue Lymphomas: solid tumors that grow in the tissues of the lymphatic system Leukemia: grow in blood-forming tissues