Download Section 2 Gene Expression in Development and

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