1. 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.

2. 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

3. 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

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 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

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

6. 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.

7. 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

8. 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

9. 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

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

11. 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

12. 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)

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

14. 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

15. 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

16. 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

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

18. 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.

19. 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.

20. 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

21. 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.

22. 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.

23. 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

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
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

26. 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

27. 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.

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.
Metastasis: spread of malignant cells beyond their original site

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.

30. 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