Table of Contents

1
Table of Contents
Gene Expression
Chapter 11

• Section 1 Control of Gene Expression
• Section 2 Gene Expression in Development and
  Cell
• Division

2
Objectives
Section 1 Control of Gene Expression
Chapter 11

• 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
Standards
Chapter 11
Gene Expression

• 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.

4
Role of Gene Expression
Section 1 Control of Gene Expression
Chapter 11

• Gene expression is the activation of a gene that
  results in transcription and the production of
  mRNA.
• Only a fraction of any cells genes are expressed
  at any one time.

5
Gene Expression in Prokaryotes
Section 1 Control of Gene Expression
Chapter 11

• 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.

6
Section 1 Control of Gene Expression
Chapter 11
Operon
Click below to watch the Visual Concept.
7
Gene Expression in Prokaryotes, continued
Section 1 Control of Gene Expression
Chapter 11

• 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.

8
Gene Expression in Prokaryotes, continued
Section 1 Control of Gene Expression
Chapter 11

• 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.

9
Section 1 Control of Gene Expression
Chapter 11
Repression of Transcription in the lac Operon
Click below to watch the Visual Concept.
10
Gene Expression in Prokaryotes, continued
Section 1 Control of Gene Expression
Chapter 11

• 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.

11
Section 1 Control of Gene Expression
Chapter 11
Activation of Transcription in the lac Operon
12
Mechanism of lac Operon
Section 1 Control of Gene Expression
Chapter 11
13
Gene Expression in Eukaryotes
Section 1 Control of Gene Expression
Chapter 11

• 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.

14
Gene Expression in Eukaryotes, continued
Section 1 Control of Gene Expression
Chapter 11

• Control After Transcription
• In eukaryotes, gene expression can be controlled
  after transcriptionthrough the removal of
  introns from pre-mRNA.

15
Removal of Introns After Transcription
Section 1 Control of Gene Expression
Chapter 11
16
Gene Expression in Eukaryotes, continued
Section 1 Control of Gene Expression
Chapter 11

• Control at the Onset of Transcription
• In eukaryotes, gene expression can be controlled
  at the onset of transcriptionthrough the action
  of regulatory proteins known as transcription
  factors.

17
Section 1 Control of Gene Expression
Chapter 11
Enhancers for Control of Gene Expression
Click below to watch the Visual Concept.
18
Controlling Transcription in Eukaryotes
Section 1 Control of Gene Expression
Chapter 11
19
Section 2 Gene Expression in Development and Cell
Division
Chapter 11
Objectives

• Summarize the role of gene expression in an
  organisms 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.

20
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.

21
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
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.

23
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.

24
Section 2 Gene Expression in Development and Cell
Division
Chapter 11
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.

25
Effect of Mutation on Gene Expression
Section 2 Gene Expression in Development and Cell
Division
Chapter 11
26
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.

27
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.