Download Section 2 Gene Expression in Development and Cell

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.
• 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
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.
• 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
Chapter 11
Section 1 Control of Gene Expression
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
Chapter 11
Section 1 Control of Gene Expression
Operon
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Visual Concept
Chapter 11
Section 1 Control of Gene Expression
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.
Chapter 11
Section 1 Control of Gene Expression
Repression of Transcription in the lac Operon
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Visual Concept
Chapter 11
Section 1 Control of Gene Expression
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
Chapter 11
Section 1 Control of Gene Expression
Activation of Transcription in the lac Operon
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Visual Concept
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 2 segments:
• Introns - noncoding sections
• exons - coding sections
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 (form of messenger RNA that
contains both introns and exons)
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 After Transcription
– After mRNA has been transcribed:
• Its introns are cut out
• Its exons are joined together
• It leaves the nucleus
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.
– Enhancer – sequence of nucleotides in a DNA
molecule that aids in arranging RNA polymerase
in the correct position on the promoter
Chapter 11
Section 1 Control of Gene Expression
Enhancers for Control of Gene Expression
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Visual Concept
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.
• 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.
Chapter 11
Section 2 Gene Expression in
Development and Cell Division
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
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.
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.
– Pg 224, Figure 11-5
– The homeoboxes of many eukaryotic organisms
appear to be very similar.
Chapter 11
Section 2 Gene Expression in
Development and Cell Division
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
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
• 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
Chapter 11
Section 2 Gene Expression in
Development and Cell Division
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
Chapter 11
Section 2 Gene Expression in
Development and Cell Division
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.
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.
– Metastasis: spread of malignant cells beyond
their original site
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.
Chapter 11
Section 2 Gene Expression in
Development and Cell Division
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