Download Chapter 11: How Genes are Controlled

BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 11
The Control of Gene Expression
Modules 11.1 – 11.11
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Researchers clone animals
by nuclear transplantation
– A nucleus of an egg cell
is replaced with the nucleus
of a somatic cell from an adult
• Thus far, attempts at human cloning have not
succeeded in producing an embryo of more
than 6 cells
– Embryonic development depends on the control
of gene expression
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• In reproductive cloning, the embryo is
implanted in a surrogate mother
• In therapeutic cloning, the idea is to produce a
source of embryonic stem cells
– Stem cells can help patients with damaged
tissues
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Donor
cell
Nucleus from
donor cell
Remove
nucleus
from egg
cell
Add somatic
cell from
adult donor
Implant blastocyst
in surrogate mother
Clone of donor
is born
(REPRODUCTIVE
cloning)
Remove embryonic
stem cells from
blastocyst and
grow in culture
Induce stem
cells to form
specialized cells
for THERAPEUTIC
use
Grow in culture to produce
an early embryo (blastocyst)
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GENE REGULATION IN PROKARYOTES
11.1 Proteins interacting with DNA turn
prokaryotic genes on or off in response to
environmental changes
• The process by which
genetic information flows
from genes to proteins is
called gene expression
– Our earliest
understanding of gene
control came from the
bacterium E. coli
Figure 11.1A
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• In prokaryotes, genes for related enzymes are
often controlled together by being grouped into
regulatory units called operons
• Regulatory proteins bind to control sequences
in the DNA and turn operons on or off in
response to environmental changes
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• The lac operon produces enzymes that break
down lactose only when lactose is present
OPERON
Regulatory
gene
Promoter Operator
Lactose-utilization genes
DNA
mRNA
RNA polymerase
cannot attach to
promoter
Active
repressor
Protein
OPERON TURNED OFF (lactose absent)
DNA
RNA polymerase
bound to promoter
mRNA
Protein
Lactose
Inactive
repressor
Enzymes for lactose utilization
OPERON TURNED ON (lactose inactivates repressor)
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Figure 11.1B
• Two types of repressor-controlled operons
Promoter
Operator
Genes
DNA
Active
repressor
Active
repressor
Tryptophan
Inactive
repressor
Inactive
repressor
Lactose
lac OPERON
Figure 11.1C
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trp OPERON
CELLULAR DIFFERENTIATION AND THE
CLONING OF EUKARYOTES
11.2 Differentiation yields a variety of cell types,
each expressing a different combination of
genes
• In multicellular eukaryotes, cells become
specialized as a zygote develops into a mature
organism
– Different types of cells make different kinds of
proteins
– Different combinations of genes are active in
each type
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Table 11.2
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11.3 Differentiated cells may retain all of their
genetic potential
• Most differentiated cells retain a complete set of
genes
– In general, all somatic cells of a multicellular
organism have the same genes
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– So a carrot plant can be grown from a single
carrot cell
Root of
carrot plant
Plantlet
Cell division
in culture
Single cell
Root cells cultured in nutrient medium
Figure 11.3A
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Adult plant
• Early experiments in animal nuclear
transplantation were performed on frogs
– The cloning of tadpoles showed that the nuclei of
differentiated animal cells retain their full
genetic potential
Tadpole (frog larva)
Frog egg cell
Nucleus
UV
Intestinal cell
Nucleus
Transplantation
of nucleus
Nucleus
destroyed
Tadpole
Eight-cell
embryo
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Figure 11.3B
• The first mammalian
clone, a sheep named
Dolly, was produced in
1997
– Dolly provided further
evidence for the
developmental
potential of cell nuclei
Figure 11.3C
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11.4 Connection: Reproductive cloning of
nonhuman mammals has applications in basic
research, agriculture, and medicine
• Scientists clone farm
animals with specific
sets of desirable
traits
• Piglet clones might
someday provide a
source of organs for
human transplant
Figure 11.4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
11.5 Connection: Because stem cells can both
perpetuate themselves and give rise to
differentiated cells, they have great
therapeutic potential
• Adult stem cells can also perpetuate themselves
in culture and give rise to differentiated cells
– But they are harder to culture than embryonic
stem cells
– They generally give rise to only a limited range
of cell types, in contrast with embryonic stem
cells
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• Differentiation of embryonic stem cells in
culture
Liver cells
Cultured
embryonic
stem cells
Nerve cells
Heart muscle cells
Figure 11.5
Different culture
conditions
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Different types of
differentiated cells
GENE REGULATION IN EUKARYOTES
11.6 DNA packing in eukaryotic chromosomes
helps regulate gene expression
• A chromosome contains a DNA double helix
wound around clusters of histone proteins
• DNA packing tends to block gene expression
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DNA
double
helix
(2-nm
diameter)
Histones
“Beads on
a string”
Nucleosome
(10-nm diameter)
Tight helical fiber
(30-nm diameter)
Supercoil
(200-nm diameter)
700
nm
Figure 11.6
Metaphase chromosome
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11.7 In female mammals, one X chromosome is
inactive in each cell
• An extreme example of DNA packing in
interphase cells is X chromosome inactivation
EARLY EMBRYO
TWO CELL POPULATIONS
IN ADULT
Cell division
and
X chromosome
inactivation
X chromosomes
Allele for
orange fur
Active X
Inactive X
Inactive X
Active X
Orange fur
Black fur
Allele for
black fur
Figure 11.7
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11.8 Complex assemblies of proteins control
eukaryotic transcription
• A variety of regulatory proteins interact with
DNA and each other
– These interactions
turn the
transcription
of eukaryotic
genes
on or off
Enhancers
Promoter
Gene
DNA
Transcription
factors
Activator
proteins
Other
proteins
RNA polymerase
Bending
of DNA
Figure 11.8
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Transcription
11.9 Eukaryotic RNA may be spliced in more than
one way
• After transcription, alternative splicing may
generate two or more types of mRNA from the
same transcript
Exons
DNA
RNA
transcript
RNA splicing
mRNA
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or
Figure 11.9
11.10 Translation and later stages of gene
expression are also subject to regulation
• The lifetime of an mRNA molecule helps
determine how much protein is made
– The protein may need to be activated in some
way
Folding of polypeptide and
formation of S–S linkages
Initial polypeptide
(inactive)
Folded polypeptide
(inactive)
Cleavage
Active form
of insulin
Figure 11.10
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11.11 Review: Multiple mechanisms regulate gene
expression in eukaryotes
• Each stage of eukaryotic expression offers an
opportunity for regulation
– The process can be turned on or off, speeded
up, or slowed down
• The most important control point is usually
the start of transcription
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Chromosome
DNA unpacking
Other changes
to DNA
GENE
GENE
TRANSCRIPTION
Exon
RNA transcript
Intron
Addition of
cap and tail
Splicing
Tail
Cap
mRNA in nucleus
NUCLEUS
Flow
through
nuclear envelope
mRNA in cytoplasm
CYTOPLASM
Breakdown of mRNA
Translation
Brokendown
mRNA
Polypeptide
Cleavage/modification/
activation
ACTIVE PROTEIN
Breakdown
of protein
Brokendown
protein
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Figure 11.11
THE GENETIC BASIS OF CANCER
11.15 Cancer results from mutations in genes that
control cell division
• A mutation can change a proto-oncogene into
an oncogene
– An oncogene causes cells to divide excessively
Proto-oncogene
Mutation within
the gene
DNA
Multiple copies
of the gene
Oncogene
Hyperactive
growth-stimulating
protein in normal
amount
Gene moved to
new DNA locus,
under new controls
New promoter
Normal growthstimulating
protein
in excess
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Normal growthstimulating
protein
in excess
Figure 11.15A
• Mutations that inactivate tumor-suppressor
genes have similar effects
Tumor-suppressor gene
Mutated tumor-suppressor gene
Normal
growthinhibiting
protein
Defective,
nonfunctioning
protein
Cell division
under control
Cell division not
under control
Figure 11.15B
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11.16 Oncogene proteins and faulty tumorsuppressor proteins can interfere with
normal signal-transduction pathways
• Mutations of these genes cause malfunction of
the pathway
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GROWTH
FACTOR
Receptor
TARGET CELL
Hyperactive
relay protein
(product of
ras oncogene)
issues signals
on its own
Normal product
of ras gene
Relay
proteins
Transcription factor
(activated)
DNA
NUCLEUS
Transcription
Protein that
STIMULATES
cell division
Translation
Figure 11.16A
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• Other cancercausing mutations
inhibit the cell’s
ability to repair
damaged DNA
GROWTHINHIBITING
FACTOR
Relay
proteins
Transcription
factor
(activated)
Receptor
Nonfunctional transcription
factor (product of faulty p53
tumor-suppressor gene)
cannot trigger
transcription
Normal product
of p53 gene
Transcription
Translation
Figure 11.16B
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Protein that
INHIBITS
cell division
Protein absent
(cell division
not inhibited)
11.17 Multiple genetic changes underlie the
development of cancer
• Cancers result from a series of genetic changes
in a cell lineage
– As in many cancers, the development of colon
cancer is gradual
Colon wall
1
Figure 11.17A
2
3
CELLULAR
CHANGES:
Increased
cell division
Growth of polyp
Growth of malignant
tumor (carcinoma)
DNA
CHANGES:
Oncogene
activated
Tumor-suppressor
gene inactivated
Second tumor-suppressor
gene inactivated
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• Mutations that lead to cancer may accumulate
in a lineage of somatic cells
Chromosomes
1
mutation
2
mutations
Normal
cell
3
mutations
4
mutations
Malignant
cell
Figure 11.17B
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11.18 Talking about Science: Mary-Claire King
discusses mutations that cause breast cancer
• Researchers have
gained insight into the
genetic basis of breast
cancer
– Studies have been done
of families in which a
disease-predisposing
mutation is inherited
Figure 11.18
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11.19 Connection: Avoiding carcinogens can
reduce the risk of cancer
• Lifestyle choices
can help reduce
cancer risk
Table 11.19
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11.12 Cascades of gene expression and cell-to-cell
signaling direct the development of an
animal
• A cascade of gene expression involves genes for
regulatory proteins that affect other genes
– It determines how an animal develops from a
fertilized egg
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• Mutant fruit flies show
the relationship
between gene
expression and
development
– Some mutants have
legs where antennae
should be
Eye
Antenna
Head of a normal fruit fly
Leg
Figure 11.12A
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Head of a developmental mutant
• Development of head-tail polarity in fruit fly
EGG CELL
WITHIN
OVARIAN
FOLLICLE
Egg cell
Egg protein
signaling
follicle cells
1
Follicle
cells
2
Gene expression in
follicle cells
Follicle cell
protein signaling
egg cell
Localization of
“head” mRNA
3
“Head”
mRNA
Figure 11.12B
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ZYGOTE
FERTILIZATION
AND MITOSIS
EMBRYO
Translation of
“head” mRNA
Gradient of
regulatory
protein
4
Gene
expression
5
Gradient of
certain other
proteins
Gene
expression
Body
segments
6
Figure 11.12B
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EMBRYO
Body
segments
6
LARVA
Gene expression
ADULT FLY
7
Head end
Tail end
Figure 11.12B
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11.13 Signal-transduction pathways convert
messages received at the cell surface into
responses within the cell
• Cell-to-cell signaling is important in
– development
– coordination of cellular activities
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• A signal-transduction
pathway that turns on
a gene
(1) The signaling cell
secretes the signal
molecule
SIGNALING CELL
1
2
TARGET CELL
(2) The signal molecule
binds to a receptor
protein in the target
cell’s plasma
membrane
Figure 11.13
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Signal
molecule
Receptor
protein
Plasma
membrane
SIGNALING CELL
Signal
molecule
1
(3) Binding activates the
first relay protein,
which then activates
the next relay protein,
etc.
(4) The last relay protein
activates a
transcription factor
Figure 11.13
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Receptor
protein
2
Plasma
membrane
3
TARGET CELL
Relay
proteins
Transcription factor
(activated)
4
SIGNALING CELL
Signal
molecule
1
Receptor
protein
2
(5) The transcription
factor triggers
transcription of a
specific gene
Plasma
membrane
3
TARGET CELL
Relay
proteins
Transcription factor
(activated)
(6) Translation of the
mRNA produces a
protein
4
NUCLEUS
DNA
5
Transcription
mRNA
New
protein
6
Figure 11.13
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Translation
11.14 Key developmental genes are very ancient
• Homeotic genes
– contain nucleotide sequences called
homeoboxes
– are similar in many kinds of organisms
– arose early in the history of life
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• Fruit flies and mice have similar homeotic
genes (colored boxes)
• The order of
homeotic genes
is the same
• The gene order
corresponds to
analogous body
regions
Fly chromosomes
Mouse chromosomes
Fruit fly embryo (10 hours)
Mouse embryo (12 days)
Adult fruit fly
Adult mouse
Figure 11.14
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