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Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Now that we understand how genes
are transcribed into RNA and how
that RNA, if it is mRNA, is translated
into a polypeptide, it is time to
understand how gene transcription
and translation are controlled in the
cell.
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Gene Regulation
(controlling gene expression – turning genes
on/off)
Gene expression = Transcription and Translation of a gene; the cell
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Multicellular organisms are composed of many
different types of cells…
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
What makes these cells different from each
other?
The same thing that makes a school
different from a bank or a police station
different from a fire house…the workers are
different!!
Differential gene expression
(Different cells have different genes turned on/off)
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Stem Cells
- cells that have the ability to differentiate (to
turn into) a specific cell type like a neuron or
muscle cell. All of their genes have the
potential to be turned on/off.
Stem Cell
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Stem Cells
Stem Cells
Stem Cell
Stem Cells can
divide to make
more stem cells
or they can
Differentiated Cells
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Active
genes
Inactive
genes
Some genes are turned off for the life of the cell:
In differentiated cells, certain genes are
“permanently” shut down by histone packing
like the insulin gene in muscle cells. There is
not reason for muscle to make insulin.
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Active
genes
Inactive
genes
Can differentiated cells turn back into stem cells
(dedifferentiate)?
This is not the norm, but is it possible?
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
Let’s try a little experiment:
1. Let’s take an ovum from some multicellular
organism like a sheep and remove the nucleus.
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
(somatic/differenti
ated cell’s nucleus)
Let’s try a little experiment:
2. Then let’s take the nucleus from a differentiated cell
and put it into the ovum (this is a diploid nucleus of
course).
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
(somatic/differenti
ated cell’s nucleus)
Let’s try a little experiment:
A. What do you predict should happen if differentiated
cells can never access the silenced genes?
B. What if the genes can be turned back on?
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
The cells of the embryo
are called embryonic
stem cells.
What type of cells can
embryonic stem cells
differentiate into?
These will become the
organism so ALL CELL
TYPES!
Let’s try a little experiment:
3. It turns out that the genes can be reactivated (they are
not permanently turned off) and the “zygote” divides to
become
anconception
embryo. (fertilization) to eight weeks old
Embryo =
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
Let’s try a little experiment:
3. It turns out that the genes can be reactivated (they are
not permanently turned off) and the “zygote” divides to
become
an embryo.
What
would
you try next?
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
Let’s try a little experiment:
4. We can try to implant the embryo into the uterus of a
surrogate mother (a black face ewe in this case) and see
what happens…
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
Let’s try a little experiment:
5. Amazingly, the embryo develops and the lamb is born.
This lamb is a clone (genetically identical) to the ovum
The nucleus
donor as the nucleus contained the
donor or the nucleus
donor?
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is it possible for a differentiated cell to
dedifferentiate back to a stem cell?
This process is called REPRODUCTIVE CLONING.
Does this answer the above question?
This indicates that genes in a differentiated nucleus have the
“potential” to reactivate and therefore differentiated cells will
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
Is is possible for a differentiated cell to
dedifferentiate back to a stem cell?
REPRODUCTIVE CLONING
Dolly (left) and her
surrogate mother. A black
face sheep cannot give
birth to a white face sheep
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
What could reproductive cloning be used for?
1. Repopulating endangered species…is there a
They are all genetically identical and therefore equally
problem?
susceptible to the same environmental changes…
2. Clone drug-producing animals
3. Clone genetically-unique animals, etc…
Should we do this with humans?
What if you had a
reproductive clone. One
day you fell ill and needed
part of a liver or a kidney or
bone
marrow?...
There
are
arguments on both
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
How many different animals have been cloned thus
far?
At least 20 ranging from camels, cats, dogs, a horse
all the way to fish, frogs and fruit flies.
Cloned cats…
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
How many different animals have been cloned thus
far?
At least 20 ranging from camels, cats, dogs, a horse
all the way to fish, frogs and fruit flies.
Cloned cats…that have been
genetically modified (next chapter)
Chapter 11 - The Control of Gene Expression
AIM: What is the effect of differentiated gene expression?
?
What else could we do with this embryo?
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
We can grow them in a dish (culture them) and then treat the
cells with different hormones to get them to differentiate into
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
What can we use these differentiated cells for?
One could make any cell type they want:
1. Skin cells for burn victims
2. Organs for transplant patients
3. Neurons for a person with a
spinal cord injury
4. Basic scientific research, etc…
What is the advantage of these cells over other neurons
or organs in terms of transplants?
These transplanted cells will not be rejected (destroyed by the
immune system) because they are genetically identical to the
patient (your antibodies will not bind to them).
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
This form of cloning is called Therapeutic Cloning.
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
Ethics
Should we be able to use embryos
to get embryonic stem cells?
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
Recent advances:
In 2008, scientists at UCLA figured out how to turn skin
cells into embryonic stem cells, alleviating the need for
cloning and embryo destruction
Kathrin Plath, UCLA stem cell scientists
http://www.sciencedaily.com/releases/2008/02/080211172631.htm
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
Adult stem cells
- Stem cells found within us amongst the
differentiated stem cells
- Unlike embryonic stem cells, adult stem cells
cannot become every cell type…
Ex. Hematopoietic stem cells
- Found in the bone marrow
- Divides to make more stem cells,
some of which differentiate into all
the types of blood cells.
- Can be used to treat leukemia or
possibly even HIV!
Chapter 11 - The Control of Gene Expression
AIM: Do differentiated cells retain their genetic potential?
What
http://www.nature.com/nm/journal/v15/n4/full/nm0409-371.html
Chapter 11 - The Control of Gene Expression
AIM: Do differentiated cells retain their genetic potential?
Where else do we observe already differentiated
cells dedifferentiating and becoming other cells
types?
Regeneration
- Regrowth of a lost of damaged body
part
Chapter 11 - The Control of Gene Expression
AIM: Do differentiated cells retain their genetic potential?
What about plants?
Can differentiated cells dedifferentiate into stem
cells?
Chapter 11 - The Control of Gene Expression
AIM: Do differentiated cells retain their genetic potential?
Fig. 11.3A
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
Review
- Stem Cells
- Therapeutic vs. Reproductive cloning
- Embryonic vs. adult stem cells
Chapter 11 - The Control of Gene Expression
AIM: How are stem cells generated and used?
Now not all genes are going to be silenced for
the life of the cell/organism…
Ex. The genes coding for enzymes that make
glycogen in the liver…
If the blood glucose concentration is low, the liver
will be releasing glucose, not building glycogen
from it. Therefore, the genes should be off.
Likewise the genes whose protein products are
involved in secreting glucose should be on.
Gene are CONSTANTLY being turned on and off
in Let’s
yourlook
cells
at how this is accomplished in prokaryotes and then in
Chapter 11 - The Control of Gene Expression
NEW AIM: How are genes regulated (controlled) in prokaryotes?
How are genes regulated in
prokaryotes?
Fig. 11.1A
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
In order to begin to understand this process, we
will look at a set of three genes involved in
Glucose
and galactose
lactose metabolism (the
hydrolysis
of lactose to
_______________) called the…
Lactose (Lac) Operon
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
LacA
Anatomy of an operon
The terminator
An operon typically contains a:
sequence
1. Promoter
2. Operator
3. A set of genes (3 in this specific case)
A. LacZ
B. LacY
C. LacA
4. What critical gene part is missing from this figure?
The terminator sequence
The regulatory gene (LacI) is found OUTSIDE of the operon.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
LacA
The three gene products (can you guess what they might be?):
1. LacZ codes for β-galactosidase
- The enzyme that hydrolyzes lactose to glucose
and galactose
2. LacY codes for permease
- A passive lactose transporter protein that sits in
the membrane and allow lactose to diffuse into the
cell.
3. LacA codes for transacetylase
- Exact function not yet known…
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
QUESTION
If lactose is present around the cell (perhaps it is one of the
bacterium in your mouth and you just drank a glass of
milk), should these genes be turned on or off?
They should be ON since lactose is present and will need to be
hydrolyzed so the glucose can be used to make ATP of for
biosynthesis.
Let’s look at how this operon works to control expression of these three
genes…
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
1. The regulatory gene codes for the repressor protein.
A. What does repress mean?
- To prevent
B. What will this protein do then?
- It will prevent the expression of the genes (turn them
Fig. 11.1B - Any guess how it might do this?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
1. The regulatory gene codes for the repressor protein.
C. It represses by binding to the Operator sequence.
Fig. 11.1B
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
1. The regulatory gene codes for the repressor protein.
C. It represses by binding to the Operator sequence.
-When it binds the operator, it will interfere with RNA
polymerase binding to the promoter. The genes are
off.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
ALL FOR ONE AND ONE FOR ALL
Notice that all three genes are turned on/off together.
Eukaryotes do not typically do this. They turn genes on/off
individually.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Fig. 11.1B
Q1. How do you suppose these genes will be turned ON when lactose is
present?
A1. Somehow the repressor needs to fall off.
Q2. How can we get it to fall off? (HINT: you are changing its
function)
A2. You need to change its structure.
Q3. How can we change the structure?
A3. Bind something to it…a ligand.
Q4. What should the ligand be?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
The ligand should be lactose itself since in the presence of lactose
these genes should be turned ON.
Fig. 11.1B
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Activating the operon:
1. Lactose binds the repressor.
2. A conformational (shape) change occurs and the repressor falls off
the operator.
3. RNA polymerase now binds to the promoter and begin
transcription of all three genes in one long mRNA.
4. Ribosomes translate the mRNA into proteins.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Q1. What will happen when β-galactosidase breaks down most of the
lactose?
A1. Lactose will fall off the repressor and the repressor will once
again bind to the operator and turn the genes off.
Q2. Why not just leave these genes on all the time?
A2. This would be a huge waste of resources…ATP, amino acids,
ribosomes, nucleotides, RNA polymerases and space.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Lac repressor
protein
Repressor bound to
the operator
Lac operon – The
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
- This operon contains fours genes whose
protein products are responsible for
synthesizing (making) the amino acid
tryptophan.
When would you want to turn these genes
on?When tryptophan is NOT present,
because that is when you need to make
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
When would you want to turn these genes
on?When tryptophan is NOT present,
because that is when you need to make
it…
How does this compare to the lac
operon?
It is the opposite. You turn
the lac genes ON when
lactose is present.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
Q. Tryptophan binds to the trp repressor just
like lactose binds to the lac repressor. How
does this work?
What you know:
1. Trp binds to repressor
2. When Trp is present,
trp synthesis genes are
off
A. The repressor is active
when Trp is bound and
inactive when it is not,
the opposite of the lac
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Tryptophan (Trp) operon
I do not recommend memorizing the difference.
Think about is logically:
1. The repressor bind to the operator
2. When it is bound the genes are off
3. You need the lactose break down genes
when lactose is present.
4. Therefore, when lactose binds to
repressor, it should fall off operator
5. Likewise, when trp is present, the trp
synthesis genes are unnecessary because
you
have it already
6. Therefore,
Trp when Trp binds to the
repressor, the repressor should bind the
operator and shut the genes off.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
Trp operon
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated (controlled) in prokaryotes?
The trp repressor
(with trp bound)
binding to the
operator sequence.
Chapter 11 - The Control of Gene Expression
NEW AIM: How are genes regulated in eukaryotes?
How are eukaryotic genes
regulated?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
1.
2.
3.
4.
5.
6.
7.
DNA packing
Transcription initiation
Splicing
mRNA degradation
Translation initiation
Protein activation
Protein Breakdown
Fig. 11.11
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
1. DNA
Packing
Histones can pack genes or
entire segments of
chromosomes tightly such
that transcription factors
and RNA polymerases
cannot access the DNA.
These gene are typically
turned off for the life of the
cell.
Fig.
11.6
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
Fig. 11.6
Ex. One of the X chromosomes in XX females (humans
included) is randomly silenced by histones. Females, like
males, only have one active X chromosome. The other is
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
Fig. 11.6
Ex. One of the X chromosomes in XX females (humans
included) is randomly silenced by histones. Females, like
males, only have one active X chromosome. The other is
Recall Transcription
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
2. Transcription Initiation
- Transcription factors are
required to start
transcription.
- Some of these proteins
will bind at the promoter.
- Others will bind at
sequences distant from the
gene itself called enhancer
sequences.
NO TF’s, NO Transcription
Fig. 11.8
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
2. Transcription Initiation
EXAMPLE:
a. A signal molecule (ligand)
like growth factor will bind to a
surface receptor.
b. Signal transduction occurs
and a TF is activated.
c. This TF will enter the nucleus
and turn on genes involved in
activating cell division.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
3. Alternative splicing
- Alternative splicing
can control how much
mRNA is synthesized
of each alternative
transcript.
Fig. 11.9
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
4. mRNA degradation
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
5. Translation Initiation
Like transcription, translation
also requires other proteins to
start called initiation factors
(IF’s).
NO IF’s, NO Translation
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
Fig. 11.10
6. Protein activation
(pre-insulin)
Insulin is made as a single polypeptide, which then fold into its
inactive form. An enzyme will cut (cleave) the polypeptide
forming the active protein form of insulin.
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
Eukaryotic gene regulation
7. Protein Degradation
When a protein is no longer
needed (the cell has enough
product of a certain enzyme) it can
broken
down –into its amino
be degraded
acids, which are then recycled
into new polypeptides.
This is accomplished by a large
assembly (complex) of proteins called
the proteosome.
It is really a “polypeptide shredder”.
AIM: How are genes regulated (controlled) in eukaryotes?
Chapter 11 - The Control of Gene Expression
AIM: How are genes regulated in eukaryotes?
1.
2.
3.
4.
5.
6.
7.
DNA packing
Transcription initiation
Splicing
mRNA degradation
Translation initiation
Protein activation
Protein Breakdown
Clearly more complex than prokaryotes…
Fig. 11.11
Chapter 11 - The Control of Gene Expression
NEW AIM: What is the genetic basis of cancer?
How does one get cancer?
Mutations in the DNA of genes
responsible for controlling the cell
cycle (cell division).
The products of these genes are typically
involved in regulating gene expression…
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
Signal transduction pathway
- process by which the cell
converts one signal into
another
In this case (to the right) an
external signal is converted
into an multiple internal
signal through relay
proteins.
Fig. 11.15A
Chapter 11 - The Control of
growth factor (GF)
Gene Expression
AIM: What is the genetic
basis of cancer?
Let’s say the signal
molecule (ligand) is growth
factor (GF) and the new
proteins being made
activate cell division.
Activate
division
Fig. 11.15A
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
If there were no growth
factor there should be no…
Activate
division
Fig. 11.15A
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
If there were no growth
factor there should be no…
…new protein being made
and cell division should….
be off.
Q. What if there is a
mutation in the gene of one
of the relay proteins that
changes its shape so that it
is always on?
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
The transduction pathway will
always be on regardless of
growth factor…
This can lead to uncontrolled
cell division…cancer.
Fig. 11.16A
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
Proto-oncogene
A gene that when modified
causes cancer is called a
proto-oncogene.
Oncogene
The mutated form of the gene.
Proto = “before”
oncos = “tumor” or cancer
Gene = gene
Chapter 11 - The Control of Gene Expression
AIM: What is the genetic basis of cancer?
Fig. 11.15A
How a proto-oncogene can become an oncoge
- proto-oncogenes are often signal transduction
proteins that promote cell division
Chapter 11 - The Control of Gene Expression
AIM: What is the genetic basis of cancer?
Fig. 11.15A
If you get a mutation in a proto-oncogene, does that
mean you get cancer?
No, it takes more than one mutation in one gene to
cause cancer…read on.
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
Cells have genes that code for
proteins that inhibit cell
division called tumor
suppressor genes.
They are typically TF’s that
activate proteins, which
prevent cell division or
cause apoptosis.
Fig. 11.16B
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
What would need to happen in
order to get cancer in a cell
that already has an oncogene?
Chapter 11 - The Control of
Gene Expression
AIM: What is the genetic
basis of cancer?
You would need a mutation in
BOTH tumor suppressor
genes…why?
Just because you knocked out one, the other
can still function and stop the division (two hit
hypothesis).
Why don’t both protooncogenes need to be
These
proteins activate and you only need one
modified/mutated?
oncogene to activate the pathway.
Fig. 11.16B
AIM: What is the genetic basis of cancer?
Both BRCA1 and BRCA2
are DNA repair proteins fixes breaks.
Mutations in the BRCA1
gene increase the risk
breast, ovarian, Fallopian
tube, prostate and colon
cancers.
Over 600 different mutations have
been identified
Among breast cancer patients of
Jewish ancestry, 10% had mutations
in one of these two genes.
Fig. 11.16B
Chapter 11 - The Control of Gene Expression
AIM: What is the genetic basis of cancer?
Fig. 11.17A
Chapter 11 - The Control of Gene Expression
AIM: What is the genetic basis of cancer?
Fig. 11.17B
Chapter 11 - The Control of Gene Expression
AIM: What is the genetic basis of cancer?
Conclusion:
1. Multiple mutations are required for cancer to occur
a. A proto-oncogene must be mutated to an oncogene
promoting cell growth
b. Tumor suppressor genes must be mutated and
rendered inactive so they don’t inhibit division or cause
apoptosis.
Chapter 11 - The Control of Gene Expression
AIM: What is the genetic basis of cancer?