Transcript Chapter 11

CONTROL OF GENE
EXPRESSION
Copyright © 2009 Pearson Education, Inc.
DNA from Cell to Cell
 There are many types of cells in the human body
 Skin, brain, liver, heart, muscle
 Functions and structures of each differ, ex.
 How does this happen?
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DNA from Cell to Cell
 Two hypotheses
 Is there different DNA in each cell so that each cell has and will
therefore express different genes?
 Is the DNA the same in each cell but it is regulated so that each
cell expresses different genes?
 Each of these mechanisms would result in the different types of
cells that we see in our body
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Differentiation results from the expression of
different combinations of genes
 Differentiation involves cell specialization, in
both structure and function
 Most differentiated cells retain a complete set of
their genes, but just don't express all of them
 Differentiation is controlled by turning specific
sets of genes on or off
 For example: in the muscle cell
 On – muscle contraction protein genes, glycolysis
enzymes
 Off – lactation producing enzymes, calcification enzymes
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Which of the following
cells would likely
express the genes
that code for
glycolysis enzymes?
1)
Muscle cell
2)
White blood cell
3)
Pancreas beta
cells
4)
All of these cells
5)
None of these
cells
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Answer
Which of the following
cells would likely
express the genes
that code for
glycolysis enzymes?
4)
All of these
cells
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Which of the following
cells would likely
express the genes that
code for the hormone
insulin?
1)
Muscle cell
2)
White blood cell
3)
Pancreas beta
cells
4)
All of these cells
5) None of these
cells
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Answer
Which of the following
cells would likely
express the genes that
code for the hormone
insulin?
3)
Pancreas beta
cells
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Which of the following
cells would likely
express the genes that
code for the hormone
gastrin?
1)
Muscle cell
2)
White blood cell
3)
Pancreas beta
cells
4)
All of these cells
5) None of these
cells
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Differentiation results from the expression of
different combinations of genes
 In other words each cell has the same DNA
as every other cell in the body.
 A muscle cell has the same genes that make
mammary glands produce milk, but the
muscle cell is not using them
 All cells have the same genetic blue print
 How do they become specialized? Who tells
them what genes to express?
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The answer is found even earlier in development than
this fetus
Photo: http://www.solarnavigator.net/images/baby_in_mothers_womb.jpg
11.10 Cascades of gene expression direct the
development of an animal
 Early genes in the egg produce proteins and
mRNAs that establish which end of the embryo
will be the head and which end will be the tail
o Homeotic genes are master control genes that determine the
anatomy of the body, specifying structures that will develop in
each segment
 The egg is fertilized and mitosis occurs repeatedly
 As the cells divide the mRNA is translated and the
proteins direct the differentiation of the cells
 The end result is subdivision of the embryo into
different levels/tissue types
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Development of Head-Tail Axis in Fruit Flies
 These genes act in
sequential order, with
products of one set of genes
influencing the activity of
the next set of genes, to
define and organize smaller
and smaller regions of the
embryo.
 While in the embryo each
cell begins to differentiate
o So each cell does not have the
potential to become any cell
type in the body
o But still retains the ability to
become many different cell
types
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Egg cell
Egg cell
within ovarian
follicle
Follicle cells
Protein
signal
1
“Head”
mRNA
2
Embryo
3
Gene expression
Cascades of
gene expression
Body
segments
Gene expression
Adult fly
4
This mutant is the result of misexpression of genes downstream from a homeotic gene
Eye
Antenna
Leg
Head of a normal fruit fly
Head of a developmental mutant
How are all of the genes
regulated?
What are the mechanics of turning one
gene on or another gene off?
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11.1 Proteins interacting with DNA turn
prokaryotic genes on or off in response to
environmental changes
 Gene expression is the overall process of
information flow from genes to proteins
 If a gene is being expressed it is usually being
transcribed
– Mainly controlled at the level of transcription
– A gene that is “turned on” is being transcribed to
produce mRNA that is translated to make its
corresponding protein
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11.1 Proteins interacting with DNA turn
prokaryotic genes on or off in response to
environmental changes
 As we saw with the muscle cell, the pancreas cell,
and the blood cell, each cell type needs to be able
to regulate which genes are turned on or off
 This is done mainly by proteins interacting with
DNA
 Lets look at a prokaryotic
example of gene regulation in E.
coli
 Eukaryotic cells get much more
complicated
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Lets say that the E. coli bacterium has a sudden
need to digest lactose. It will need the
enzyme necessary to perform that action.
 Lets talk about three adjacent genes that code for
lactose-digestion enzymes
 All regulated together
– Promoter sequence where RNA polymerase binds
– Operator sequence is where a repressor can bind
and block RNA polymerase action
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The E. coli needs to turn on the lac operon, but
how?
 Regulation of the lac operon
– Repressor protein
– In the absence of lactose, the repressor binds to the
DNA and prevents RNA polymerase action
– When lactose is in the cell it will need to be
digested, so the cell has a way of turnign the genes
on
– Lactose binds to the repressor and the repressor
falls of, so the DNA is unblocked
– RNA polymerase can now transcribe the genes
needed for the cell
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OPERON
Regulatory Promoter Operator
gene
Lactose-utilization genes
DNA
mRNA
Protein
Active
repressor
Operon turned off (lactose absent)
RNA polymerase
cannot attach to
promoter
DNA
mRNA
RNA polymerase
bound to promoter
Protein
Lactose
Inactive
repressor
Enzymes for lactose utilization
Operon turned on (lactose inactivates repressor)
OPERON
Regulatory Promoter Operator
gene
Lactose-utilization genes
DNA
mRNA
Protein
RNA polymerase
cannot attach to
promoter
Active
repressor
Operon turned off (lactose absent)
DNA
mRNA
RNA polymerase
bound to promoter
Protein
Lactose
Inactive
repressor
Operon turned on (lactose inactivates repressor)
Enzymes for lactose utilization
Eukaryotic genes can be controlled in a similar
way (by proteins influencing the behavior of
RNA polymerase)
 Eukaryotic genes
– Each gene has its own promoter and terminator (on
the DNA)
– Are usually switched off and require activators to be
turned on
– Are controlled by numerous regulatory proteins
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11.5 Complex assemblies of proteins control
eukaryotic transcription
 Regulatory proteins that bind to control
sequences
– Transcription factors promote RNA polymerase
binding to the promoter
– Activator proteins bind to DNA enhancers and
interact with other transcription factors
– Silencers are repressors that inhibit transcription
 Control sequences
– Promoter
– Enhancer
– Related genes located on different chromosomes can be
controlled by similar enhancer sequences
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11.5 Complex assemblies of proteins control
eukaryotic transcription
Animation: Initiation of Transcription
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Enhancers
Promoter
Gene
DNA
Activator
proteins
Transcription
factors
Other
proteins
RNA polymerase
Bending
of DNA
Transcription
11.3 DNA packing in eukaryotic chromosomes
helps regulate gene expression
 Eukaryotic chromosomes undergo multiple levels
of folding and coiling, called DNA packing
– DNA is wrapped around proteins called
histones
 DNA packing can prevent transcription
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Metaphase
chromosome
Tight helical fiber
(30-nm diameter)
DNA double helix
(2-nm diameter)
Linker
“Beads on
a string”
Nucleosome
(10-nm
diameter)
Histones
Supercoil
(300-nm diameter)
700 nm
NUCLEUS
Chromosome
Many other
ways of
regulating
which genes
are expressed
DNA unpacking
Other changes to DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of cap and tail
Splicing
Tail
mRNA in nucleus
Cap
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
Cloning
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Turning People Into Product
Specter Of Cloning May Prove A Mirage
F.D.A. Says Food From Cloned Animals Is Safe
Cloning:Where Do We Draw the Line
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Dolly the Sheep
Why was Dolly important?
What were the starting materials for making Dolly?
How is this different from sexual reproduction?
Why is cloning not more common place?
Whatever happened to Dolly?
Cloning
Why do people want to clone organisms?
a. to help infertile couples have children
b. to produce desirable organisms for research and
agriculture
c. to save endangered species from extinction
d. to produce embryos for harvesting stem
cells
e. All of these have
been proposed as
justification for
cloning.
Summary
The cloning of Dolly the sheep demonstrated that the
nuclei from differentiated mammalian cells can retain their
full genetic potential.
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Summary
• In sexual reproduction, genetic information from
two parents is combined to form unique
individuals.
• Cloning produces a copy of one individual.
• As cells age, they specialize. But this process may
be artificially reversed to produce a new individual.
• In cloning, the nucleus is removed from a donor
cell and replaced with the nucleus from another
individual.
• Cloning is proposed as a way to preserve
endangered species.
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 Imagine for a moment that your daughter needs a
bone-marrow transplant and no one can provide a
match; that your wife's early menopause has made
her infertile; or that your five-year-old has drowned
in a lake and your grief has made it impossible to
get your mind around the fact that he is gone
forever.
 Our two-year-old daughter died in a car crash; we
saved a lock of her hair in a baby book. Can you
clone her? Why does the law allow people more
freedom to destroy fetuses than to create them?
My husband had cancer and is sterile. Can you help
us?
 Current Opinion in 2001:
“The consensus among biotechnology specialists is
that within a few years--some scientists believe a
few months--the news will break of the birth of the
first human clone.”

Time: Baby, It's You! And You, And You...
Lets say humans are eventually cloned
 On what grounds could reproducing children by cloning
be allowed or prohibited?
 Should cloning be used for sterile couples or for
homosexual couples who want biological offspring?
 How would a child born by asexual reproduction
experience life, as a unique individual or as a genetic
“prisoner”?
 Is a cloned child simply a twin of its genetic donor, with
a certain time lag?
 How would you deal with property rights and inheritance
with clones?
 If you cloned your daughter, father, dog, etc,
would the clone look and act just as the original?
Can you actually replace a living being?
Whatever happened to Dolly?
 Euthanized at age of 6 after being diagnosed with
progressive lung disease.
 She also had arthritis.
 Dolly had DNA in her cells that was typical of an
older animal.
 It was not clear whether the cloning process led to
the arthritis, but research in 1999 suggested that
Dolly might be susceptible to premature aging.
Therapeutic vs. Reproductive Cloning
Donor
cell
Nucleus from
donor cell
Reproductive
cloning
Implant blastocyst in
surrogate mother
Remove
nucleus
from egg
cell
Add somatic cell
from adult donor
Grow in culture
to produce an Therapeutic
early embryo cloning
(blastocyst)
Remove embryonic
stem cells from
blastocyst and
grow in culture
Clone of
donor is born
Induce stem
cells to form
specialized cells
The ultimate aim of therapeutic cloning is to supply cells for the repair of
damaged or diseased organs, not create a new individual.
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Therapeutic cloning can produce stem cells with
great medical potential
 Stem cells can be induced to give rise to
differentiated cells
– Embryonic stem cells can differentiate into a variety
of types
– Adult stem cells can give rise to many but not all
types of cells
 Therapeutic cloning can supply cells to treat
human diseases
 Research continues into ways to use and produce
stem cells
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Adult Stem Cells vs Embryonic Stem Cells
Blood cells
Adult stem
cells in bone
marrow
Nerve cells
Cultured
embryonic
stem cells
Heart muscle cells
Different culture
conditions
Different types of
differentiated cells
Therapeutic cloning can produce stem cells with
great medical potential
 Some disorders that therapeutic cloning could
potentailly help
 Parkinson’s
 Huntington’s
 Stroke
 Diabetes
 Cancer
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Spinal Cord Injuries
 The major neural cells of the central nervous system
typically do not regenerate after injury.
 If a nerve cell is damaged due to disease or injury,
there is no treatment at present to restore lost
function.
 In the case of spinal cord injuries, patients are often
left partly or wholly paralyzed because nerve and
supporting cells in the spinal cord have been
damaged and cannot regenerate.
 Such patients are permanently disabled, often
institutionalized and may require life support.
 First Stem Cell Clinical Trial Approved by
the FDA
 Spinal Cord Injury
 In January 2009, Geron received clearance from
the FDA to begin the world's first human clinical
trial of an embryonic stem cell-based therapy. The
FDA-approved clinical study is a Phase I multicenter trial designed to assess the safety and
tolerability of stem cells in patients with no motor
or sensory function.
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Biology and Society
Embryonic stem cells are currently derived from extra human
blastocysts that sometimes result from in vitro fertilization
techniques. Barak Obama lifted federal funding restrictions
on embryonic stem cell research.
“In 2001, President George W. Bush limited federal money for
human embryonic stem cell research to 21 pre-existing stem
cell lines, or families of cells derived from individual
embryos.
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Biology and Society
Under those rules, scientists would have had to ensure that
federal funds were not used to buy even the plastic pens
used to write down observations from experiments on
unapproved cells.
Obama's executive order now allows federally funded
researchers to use hundreds of new embryonic stem cell
lines. The reversal means some of the $10 billion for health
care research in the president's stimulus package likely
would go to stem cells.” AP March 10, 2009
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Biology and Society
Other countries have operating their research under little restriction
while the US has had funding restricted. Now Obama has reversed
the restrictions.
Do you support the current reversal of the U.S. governmental
policy on stem cell research?
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Biology and Society
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Biology and Society
This insufficiently developed human embryo was produced by
inserting a nucleus from an adult cell into a human egg cell—a
potential clone. The purpose was to develop embryonic stem cells.
An embryonic stem cell can potentially develop into any of the
specialized cell tissues/organs of an adult.
Despite its promise, do you think that therapeutic cloning is
ethically justifiable?
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THE GENETIC BASIS
OF CANCER
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Cell cycle control system
– A set of molecules, including growth factors, triggers
and coordinates events of the cell cycle
 Checkpoints
– Control points where signals regulate the cell cycle
– G1 checkpoint allows entry into the S phase or causes the
cell to leave the cycle, entering a nondividing G0 phase
– G2 checkpoint
– M checkpoint
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G1 checkpoint
G0
Control
system
G1
M
M checkpoint
G2 checkpoint
G2
S
11.18 Cancer results from mutations in genes
that control cell division
 Mutations in two types of genes can cause cancer
1. Tumor-suppressor genes
– Normally inhibit cell division
– Mutations inactivate the genes and allow uncontrolled
division to occur
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Example 1
• Normally Functioning Rb prevents S phase entry until everything is in order
• Once Rb gives the green light then S phase will start
G1 checkpoint
GRB
0
Control
system
G1
M
M checkpoint
G2 checkpoint
G2
S
• Suppose Rb stops functioning (is mutated)
• What will happen to the cell cycle?
11.18 Cancer results from mutations in genes
that control cell division
 Tumor-suppressor genes
– Promote cancer when copies on each chromosome
are mutated and become nonfunctioning
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11.18 Cancer results from mutations in genes
that control cell division
 Mutations in two types of genes can cause cancer
1. Tumor-suppressor genes
– Normally inhibit cell division
– Mutations inactivate the genes and allow uncontrolled
division to occur
2. Oncogenes
– Proto-oncogenes normally promote cell division
– Mutations to oncogenes enhance activity
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•
•
•
•
Ras is a protein that signals a cell to divide
Suppose it is mutated to a form that makes it hyperactive
Suppose the cell produces too much of it?
What will happen to the cell cycle?
Ras
11.18 Cancer results from mutations in genes
that control cell division
 Oncogenes
– Promote cancer when present in a single copy
– Can be viral genes inserted into host chromosomes
– Can be mutated versions of proto-oncogenes, normal
genes that promote cell division and differentiation
– Converting a proto-oncogene to an oncogene can
occur by
– Mutation causing increased protein activity
– Increased number of gene copies causing more protein to
be produced
– Change in location putting the gene under control of new
promoter for increased transcription
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Tumor-suppressor gene
Mutated tumor-suppressor gene
Normal
growthinhibiting
protein
Defective,
nonfunctioning
protein
Cell division
under control
Cell division not
under control
Three ways genes can be converted to oncogenes (cancer causing genes)
Proto-oncogene DNA
Multiple copies
of the gene
Mutation within
the gene
New promoter
Oncogene
1
2
Hyperactive
growthstimulating
protein in
normal
amount
Gene moved to
new DNA locus,
under new controls
3
Normal growthstimulating
protein
in excess
Normal growthstimulating
protein
in excess
Summary
 Normal cells can become cancerous
− When a proto-oncogene is converted to an oncogene
− A tumor suppressor gene is damaged
− Excessive replication of proto-oncogenes; Too much
production of proto-oncogenes
11.19 Multiple genetic changes underlie the
development of cancer
 Four or more somatic mutations are usually
required to produce a cancer cell
 Where do these mutations come from?
 Genetic/inherited
 Viruses
 UV exposure/radiation
 Carcinogenic chemicals

Tobacco smoke

Asbestos

Heterocyclic amines (HCA)

Etc.
–
Antioxidants can fight some
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11.19 Multiple genetic changes underlie the
development of cancer
 Four or more somatic mutations are usually
required to produce a cancer cell
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Here is an example with colon cancer
• 3 mutations cause a malignant carcinoma
Colon wall
1
2
Cellular Increased
changes: cell division
Growth of polyp
DNA
Oncogene
changes: activated
Tumor-suppressor
gene inactivated
3
Growth of malignant
tumor (carcinoma)
Second tumorsuppressor gene
inactivated
Growing out of control, cancer cells produce
malignant tumors
 It is estimated that 1,437,180 people will be diagnosed
with and 565,650 men and women will die of cancer in
2008 in the US
 No cure for cancer because of the high variability of the
disease between type and individuals

Mutations vary between individuals

So how can you give one drug for cancer when it is caused by so many
different problems/mutations within the individual or the population?

Usually caner therapies include a “cocktail” of drugs

Surgery

Radiation

Stem cell transplant
SEER Cancer Statistics
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Interpreting Data
Cancer results from several, accumulated gene mutations in a
single somatic cell, which of the following graphs would describe
the incidence rate of cancer as a function of age? Hint: The
probability of cancer would increase with additional mutations.
1.
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2.
3.
Answer
If cancer results from several, accumulated gene mutations in a
single somatic cell, which of the following graphs would describe
the incidence rate of cancer as a function of age? Hint: The
probability of cancer would increase with additional mutations.
1.
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2.
3.
Interpreting Data
Which graph best represents the natural occurrence of cancer
as a function of age?
1.
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2.
3.
Answer
Which graph best represents the natural occurrence of cancer
as a function of age?
1.
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2.
3.
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How to help prevent cancer
At least two-thirds of the cases of cancer are caused
by environmental factors
This gives hope that you can reduce your risk by
influencing your environment
1.
Avoid tobacco products
2.
Lose weight if you are overweight
3.
Diet – avoid large amounts of red meat and eat lots of
foods from plants
4.
Avoid too much sunlight, use sunscreen
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