Chapter 11 Table of Contents Section 1 Control of Gene Expression Section 2 Gene Expression in Development and Cell Division

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. Only a fraction of any cell’s genes are expressed at any one time.

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 specific products and the regulatory elements that control these genes. In prokaryotes, the structural genes, the promoter, and the operator collectively form an operon.

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. An operator is the segment of DNA that acts as a “switch” by controlling the access of RNA polymerase to the promoter.

Gene Expression in Prokaryotes, continued Section 1 Control of Gene Expression Chapter 11 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.

Gene Expression in Prokaryotes, continued Section 1 Control of Gene Expression Chapter 11 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.

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 noncoding sections, called introns, and coding sections, called exons.

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.

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 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.

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. The development of form in an organism is called morphogenesis. Both cell differentiation and morphogenesis are governed by gene expression.

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. http://learn.genetics.utah.edu/content/variation/hoxgenes/

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. 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 In Plants: Following fertilization, zygote undergoes cell division that gives rise to 1: an apical cell, which becomes the embryo and 2: a large basal cell Basal cells become the endosperm and provides nutrients from the endosperm to the growing embryo. From the eight cell stage onwards, the zygotic embryo shows clear patterns of formation which forms the main axis of polarity, and the formation of future plant structures.  controlled by homeoboxes

Apical cells – body of the embryo Basal cells – endosperm (provides nutrients)

1 totipotent: gives rise to all possible cell types Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression in Development, Stem cells – have the ability to develop into same or any differentiated cell in the body 1 totipotent: gives rise to all possible cell types 2: pluripotenet: gives rise to most but not all cell types 3. multipotent- can give rise to only a small number of different cell types In Animals (non plants): Following fertilization, zygote undergoes cell division that gives rise to three primary germ layers 1: ectoderm – outer layer, forms skin 2: mesoderm – middle layer, forms bones and muscles 3: endoderm, forms internal organs Gene expression (homeoboxes) controls future formation of various structures (arms, legs, wings, etc.)

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 Oncogenes – gene that that has the potential to cause uncontrolled cell division 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.

Gene Expression, Cell Division, and Cancer Section 2 Gene Expression in Development and Cell Division Chapter 11 Gene Expression, Cell Division, and Cancer tumors – proliferation of mass of cells that results from uncontrolled cell division Benign – usually pose no threat, easily removed Malignant – invade and destroy healthy tissues Tumor suppressor genes that code for proteins which prevent uncontrolled cell division often damaged by carcinogens (chemicals added to tobacco, asbestos, radiation, viruses).

Effect of Mutation on Gene Expression Section 2 Gene Expression in Development and Cell Division Chapter 11 Effect of Mutation on Gene Expression

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.

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.