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

2. 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.

3. 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.

4. 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.

5. 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.

7. 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.

8. 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.

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

10. 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.

11. 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.

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

13. 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.

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

15. 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.

16. 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.

17. 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.

18. 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.

19. 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

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

21. 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.)

24. 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.

25. 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.

26. 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).

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

28. 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.

29. 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.