Download DNA Replication

Molecular Genetics
Part 1 – DNA & DNA Synthesis
What is DNA?
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Stands for Deoxyribonucleic Acid
It is an organic molecule
Was known to be a chemical in cells by the end of the
nineteenth century.
Contains hereditary instructions. It is the chemical
code for every trait. The protein “blueprint”.
Can be copied and passed from generation to
generation.
DNA and RNA are both nucleic acids.
o
o
They consist of chemical units called nucleotides.
The nucleotides are joined by a sugar-phosphate backbone.
Hershey-Chase Experiment
DNA and RNA Structure
The Structure of DNA
1. Nucleotides (4 types differ in bases)
a. Phosphoric Acid
b. Deoxyribose sugar
c. Nitrogenous bases:
Adenine-Thymine
Guanine-Cytosine
2. Ladder Shape
3. Double strand, helix twist
Ladder Shape (Sides & Rungs)
The model of DNA is
like a rope ladder
twisted into a spiral.
Sides:
• Phosphoric Acid
• Sugar
• Phosphoric Acid
Rungs:
•
•
•
•
A-T
T-A
G-C
C-G
T-A
G-C
C-G
A-T
Sugar
Acid
Sugar
Acid
Sugar
Structure of DNA
The Discovery of the Double Helix
 James Watson and Francis Crick determined
that DNA is a double helix.
 Watson and Crick used X-ray crystallography data to reveal
the basic shape of DNA.
 Rosalind Franklin collected the X-ray
crystallography data.
DNA Double Helix
Chromosome DNA Code:
Genes =
• Segments of
DNA
• Code for a
trait
Hair
Color
Eye
Color
DNA Chromosome Code:
Acid
Acid
Sugar-T-A-Sugar
Acid
Acid
Sugar-G-C-Sugar
Acid
Acid
Sugar-C-G-Sugar
Triplets aka Codons
• Sets of 3 Nucleotides
• Code for Amino Acids,
that make proteins, that
ultimately code for a trait.
DNA Replication
– Chromosomes double in late
interphase - 2n to 4n
2N
– When a cell or whole organism
reproduces, a complete set of genetic
instructions must pass from one
generation to the next.
– Watson and Crick’s model for DNA suggested that
DNA replicates by a template mechanism.
– . DNA Replication Overview
DNA Replication Review
DNA Replication
• Begins at specific sites on a double helix.
• REPLICATION FORK
• Proceeds in both directions.
Leading Strand
Lagging Strand
Origins of Replication
Steps for DNA Replication:
1. DNA untwists
2. DNA unzips - HELICASE
3. Corresponding base pairs
bonded by DNA Polymerase
 Line up
 In sets of 3 nucleotides
aka “triplets” or “codons”
4. DNA reforms
5. 2 strands twist into helix
Identical
Strand
Flip to back side of “Copying DNA”
Which diagram happens 1st?
Check: When does DNA replication take place?
Copying DNA–Replication:
An Exact Copy-Practice
RNA Ribonucleic Acid
“DNA messenger & taxi”
II. RNA Structure & Function
A. What is RNA?
1. Organic Molecule
2. Stands for Ribonucleic Acid
3. Nucleic Acid
4. Three Types
1. mRNA= messenger
2. tRNA= transfer
3. rRNA= ribosomal
B. Where
1. mRNA in
nucleus &
cytoplasm
2. tRNA only in
cytoplasm
3. rRNA in the
ribosomes
is RNA located?
rRNA
mRNA
mRNA
tRNA
What is RNA’s structure?
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Acid
Sugar-Base
Acid
Sugar-Base
Acid
Sugar-Base
Acid
Sugar-Base
1. Nucleotides=
a. Phosphoric Acid
b. Ribose sugar
c. Nitrogenous
Bases:
Adenine-Uracil
Guanine-Cytocine
2. Single Strand
3. No Twisted helix
Comparison of RNA & DNA:
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Acid
Uracil
Sugar-Base
Acid
Sugar-Base
Acid
Sugar-Base
Acid
Ribose
Sugar-Base
RNA
Acid
Acid
Thymine
Sugar-Base-Sugar
Acid
Acid
Sugar-Base-Sugar
Acid
Acid
DeoxySugar-Base-Sugar
ribose
Acid
Acid
DNA Ladder
What are RNA’s functions:
1. mRNA=
• Copies the DNA code
• Deliveries message to
Ribosome
Why not send the original
DNA code out?
• DNA might be
damaged!
• mRNA
components are
reused
• To copy more
messages
Original DNA
mRNA copy
RNA function continued
tRNA
Amino
acid
2. tRNA:
• in cytoplasm
• Picks up an
amino acid
• “Taxis” the aa to
the Ribosome
protein factories
RNA function continued
3. rRNA:
• in ribosome
“protein
factories”
• Protein synthesis
III. Protein Synthesis
Assembling Proteins from the
DNA Instructions
Protein Synthesis
Transcription:
1. mRNA is copied off
of DNA
2. In nucleus
3. Steps:
• DNA untwists
• DNA unzips
• RNA codons line up
Transcription
Transcription:
DNA Code
mRNA
A
U
T
A
C
G
G
C
mRNA has:
• Ribose sugar
• Uracil
instead of
thymine
bases
• Nuclear
membrane
allows it to
leave!
Transcription the Details
The “start transcribing” signal is a nucleotide sequence
called a promoter.
– The first phase of transcription is initiation:
• RNA polymerase attaches to the promoter.
• RNA synthesis begins.
– The second phase of transcription is elongation:
• The RNA grows longer.
– The third phase of transcription is termination:
• RNA polymerase reaches a sequence of DNA bases called a
terminator.
Translation
• Conversion of
the message
(mRNA Code)
• Into a protein
• By the ribosome
factories
Translation
1. mRNA arrives at the
Ribosome (rRNA &
protein)
2. tRNA picks up an
amino acid (aa)
3. tRNA delivers the aa
to the ribosome
4. aa are assembled into
polypeptide proteins
tRNA taxi
A
U
C
G
U A G C
mRNA code
Translation: Summary
I = base (U)
II = mRNA
III = Amino acids connected by a peptide bond
IV = tRNA
V = amino acid
Translation: Details - 3 Phases
1. Initiation: Brings together:
• The mRNA
• The first amino acid with its attached tRNA
• The two subunits of the ribosome
Note: An mRNA molecule has a cap and tail that help it bind to the ribosome.
Translation Continued
2. Elongation: Also consists of several steps
• Codon recognition - The
anticodon of an incoming
tRNA pairs with the mRNA
codon.
• Peptide bond formation The ribosome catalyzes bond
formation between amino
acids
• Translocation - A tRNA
leaves the P site of the
ribosome. The ribosome
moves down the mRNA.
• Elongation continues until the ribosome reaches a stop codon.
Translation Continued
2. Termination
•
Stop codon is reached and translation ends.
Making Proteins
• How do you know
what amino acids
are being coded
for?
Summary:
DNA Replication:
• Make duplicate
DNA
• In nucleus
• Copy the
chromosomes
• For cell division
Protein Synthesis:
1. Transcription:
– Make mRNA
– From DNA
– In nucleus
2. Translation:
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–
–
–
Make protein
Off mRNA code
Using amino acids
In cytoplasm
Part IV Genetic Changes
Mutations
• Any change in the DNA sequence
• Mutations may result from
• Internal Agents such as rrrors in:
– Replication
– Transcription
– Cell Division
• Physical or chemical agents called mutagens.
– External Agents
Causes of Mutations
• Spontaneous Mutations
• Mutagens
– Agent that can cause a change in DNA
– Radiation (X-rays, cosmic rays, Ultraviolet,
nuclear)
– Chemicals (Asbestos, benzene, Formaldahyde)
– High temperatures
Chromosomal Alterations
• Sometimes parts of chromosomes are
broken off and lost during Mitosis and
Meiosis
• Break and rejoin improperly during crossing
over
• More common in plants
• Zygote usually dies, or is sterile
Mutations in Reproductive Cells
• Sperm or egg mutated can show up in offspring
• New trait
– Sometimes benefits
• Protein that doesn’t work
– Structural / functional problems
– May not survive
Mutations in Body Cells
• Not passed to offspring
• Cell divides, new cells also have mutation
• Some mutations affect cell division
– Uncontrolled cell division = Cancer
Point Mutations
• A change of a single base pair in DNA
• THE DOG BIT THE CAT
• THE DOG BIT THE CAR
Frameshift Mutation
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A single base is added or deleted
Shifts the reading of sets of 3 (codons)
THE DOG BIT THE CAT
THE DOB ITT HEC AT
What type are these?
Figure 10.21
Repairing DNA
• Enzymes proofread the DNA and replace
incorrect nucleotides.
• Specifically the enzymes and proteins
involved in replication can repair the
damage.
• Work well, but not perfect
• More exposure to a mutagen the less likely
it will be repaired
Evolution Connection
– Although mutations are often harmful,
• They are the source of the rich diversity of
genes in the living world.
• They contribute to the process of evolution
by natural selection.
Part V Applied Genetics & Gene
Regulation
Question
Haven’t our
ancestors been able
to change
the plants and
animals around them
for thousands of
years?
How? & Why?
How/Why did our ancestors modify
their plants and animals?
•cross purebreds to make hybrids…
•cross hybrids to select for recessive traits…
What types of traits were sought after?
Before the mid-1940’s, did they know
they were modifying DNA?
•What if there is not any natural variation in a species
to manipulate by breeding?
•Is it possible to artificially create mutations in
organisms and then see if those mutations can be bred?
What could we do to purposely cause mutations?
radiation
chemicals
heat
What are some types of things
scientists can do with DNA, today?
DNA fingerprinting
Identify paternity
Identify innocence/guilt
Cloning
Convince an adult cell
to grow into a whole
new organism…as if it
were a zygote.
Genetic Engineering
Taking a gene from one
organism and put it in
another organism
DNA Fingerprinting
– On November 22, 1983,
• A 15-year-old girl was raped and
murdered on a quiet country lane.
• Three years later, another 15-year-old
girl was raped and murdered.
– DNA fingerprinting of DNA samples
from suspects and the crime scene
• Proved one man guilty and another
man innocent.
– DNA technology has rapidly
revolutionized the field of forensics.
Murder, Paternity,
and Ancient DNA
– DNA fingerprinting
• Has become a standard
criminology tool.
• Has been used to identify
victims of the September
11, 2001, World Trade
Center attack.
• Can be used in paternity
cases.
– DNA fingerprinting is
also used in evolutionary
research
DNA Fingerprinting Techniques
1. The polymerase chain
reaction (PCR)
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•
a technique by which any
segment of DNA can be copied
quickly and precisely.
Through PCR, scientists can
obtain enough DNA from even
minute amounts of blood or other
tissue to allow DNA
fingerprinting.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
DNA Fingerprinting Techniques
3. Gel Electrophoresis
• Can be used to separate the DNA fragments obtained from
different sources.
– The DNA fragments are visualized as “bands” on
the gel. The bands of different DNA
samples can then be compared.
DNA Fingerprinting Techniques
2. Short tandem repeats (STRs)
• Are repetitive sequences of DNA that are repeated various
times in the genome.
• Scientists use STR analysis to compare the number of repeats
between different samples of DNA. They can prove that two
samples of DNA come from the same person.
• Once a set of DNA fragments is prepared, the next step in
STR analysis is to determine the lengths of these fragments.
Cloning
– The animals in these
pictures all share two
unusual features.
• They are all members of
endangered species, and
they are all clones.
Cloning at the Edge of Extinction
– Some scientists are now focusing their efforts
on cloning members of endangered species.
– The use of cloning to repopulate endangered
species holds tremendous promise.
Cloning Plants and Animals
The Genetic Potential of Cells
– Differentiated cells
• All contain a complete genome.
• Have the potential to express all of an organism’s genes.
– Differentiated plant cells
• Have the ability to
develop into a whole
new organism.
• The somatic cells of a
single plant can be
used to produce
hundreds of thousands
of clones.
Cloning of Animals
– Regeneration, a similar process,
• Is the regrowth of lost body parts in animals.
– Reproductive Cloning in Animals
– Nuclear transplantation
• Involves replacing nuclei of egg cells with nuclei from
differentiated cells.
• Has been used to clone a variety of animals.
– Scottish researchers cloned the first mammal in 1997.
• Dolly, the sheep, was the product of their work.
Cloning of Animals
The procedure that produced
Dolly is called reproductive
cloning.
Cloning of Animals
– Other organisms have since been produced using this
technique, some by the pharmaceutical industry.
Therapeutic Cloning and Stem Cells
– Therapeutic cloning
• Produces embryonic stem
cells (ES cells).
– Embryonic stem cells
• Can give rise to specific
types of differentiated cells.
– Adult stem cells
• Generate replacements for
nondividing differentiated
cells.
– Umbilical Cord Blood Banking
• Are unlike embryonic stem cells,
because they are partway along
the road to differentiation.
Human Therapeutic Cloning
– In 2001, a biotechnology company announced that it
had cloned the first human embryo.
Genetic Engineering aka
Recombinant DNA Technology
If a person needs a protein, but does not
have the correct gene (or if their gene for
a particular protein is mutated), …….
…..What are some examples of this?
“I have diabetes…I will die without insulin.”
“I am a hemophiliac…how can I make my
blood clot?”
…then…
How could they get that needed protein?
1. Get the protein from other humans
Problems:
We typically don’t make more of a protein
than we need…&…sharing of bodily
fluids can lead to sharing diseases…
example, before we tested blood for HIV
many hemophiliacs got HIV from blood
transfusions!
2. Use a similar protein from other animals
Example: insulin from pigs
Problems:
Sometimes the protein is close,
but not exact & can lead to rejection
problems…the process can be slow and
expensive
3. Make artificial proteins in the
laboratory from chemicals…
Problems:
very expensive and time consuming…hard to
make perfect… the process of translation in a
cell is regulated so well that there are rarely
problems…humans make lots of mistakes in
comparison!!!
4. Get bacteria (or another organism) to
make the human protein in large amounts.
REALLY FAST!
This is the thing to do…it is, NOW,
easy…cheap…and very fast!
This is called Recombinant DNA…
to take DNA from one organism and put it into
another organism in order to make a needed
protein.
Recombinant DNA Technology
– Recombinant DNA technology is a set of techniques
for combining genes from different sources into a
single DNA molecule.
• An organism that carries recombinant DNA is called a
genetically modified (GM) organism.
– Recombinant DNA technology is applied in the field
of biotechnology.
• Biotechnology uses various
organisms to perform practical
tasks.
From Humulin to Genetically
Modified Foods
– By transferring the gene for a desired
protein product into a bacterium, proteins
can be produced in large quantities.
– In 1982, the world’s first genetically
engineered pharmaceutical product was
produced.
• Humulin, human insulin, was produced by
genetically modified bacteria.
– Humulin was the first recombinant DNA
drug approved by the FDA.
Genetically Modified (GM) Foods
– Today, DNA technology is quickly replacing
traditional plant-breeding programs.
• In the United States today, roughly one-half of the corn
crop and over three-quarters of the soybean and cotton
crops are genetically modified.
– Corn has been genetically
modified to resist insect
infestation.
• This corn has been damaged by the
European corn borer.
Genetically Modified (GM) Foods
– “Golden rice” has been genetically modified to
contain beta-carotene.
• Our bodies use beta-carotene to make vitamin A.
Farm Animals and “Pharm” Animals
– While transgenic plants are used today as commercial
products, transgenic whole animals are currently only
in the testing phase.
– These transgenic sheep carry a gene for a human
blood protein.
• This protein may help in the treatment of cystic fibrosis.
Farm Animals and “Pharm” Animals
– While transgenic animals are currently used to
produce potentially useful proteins, none are yet
found in our food supply.
– It is possible that DNA technology will eventually
replace traditional animal breeding.
Recombinant DNA Techniques
– Bacteria are the workhorses of modern
biotechnology.
– To work with genes in the laboratory, biologists often
use bacterial plasmids.
• Plasmids are small, circular DNA molecules that are
separate from the much larger bacterial chromosome.
Recombinant DNA Techniques
– Plasmids can easily incorporate foreign DNA.
– Plasmids are readily taken up by bacterial cells.
• Plasmids then act as vectors, DNA carriers that move genes
from one cell to another.
– Recombinant DNA techniques
can help biologists produce
large quantities of a desired
protein.
We can Give DNA to Bacteria by…
taking a piece of DNA and cutting it to have “sticky
ends”, then cutting a plasmid to have sticky ends,
next, sticking the DNA in the plasmid, and finally,
putting the plasmid back into a bacterium.
Restriction Enzymes
Restriction enzymes cut the DNA so it has
“sticky ends”!
“Sticky
ends”
Restriction
Enzyme
What would be sticky in DNA?
The Basic Steps of Bacterial Transformation
1.
2.
3.
4.
5.
6.
7.
Cut pieces of human DNA (genes) that
code for the protein that is needed.
Cut open bacterial plasmids.
Stick the human gene in the plasmids.
Prepare bacteria to accept the plasmids
by chemically tearing small holes in the
cell walls and cell membranes & freeze
them so they don’t ooze out the holes!
Briefly heat the bacteria to make the
holes swell and allow the plasmids to
sneak inside the bacteria.
Cool & feed the bacteria so their cell
walls and membranes can heal…
Warm and feed the bacteria so they
can grow…and produce the human
protein.
Genomics and Proteomics
– Genomics is the science of studying whole genomes.
• The first targets of genomics were bacteria.
The Human Genome Project
– In 1990, an international consortium of governmentfunded researchers began the Human Genome
Project.
• The goal of the project was to sequence the human
genome.
– Sequencing of the human genome presented a major
challenge.
• It is very large.
• Only a small amount of our total DNA is contained in
genes that code for proteins.
The Human Genome Project
– The Human Genome Project
• Can help map specific disease genes such as Parkinson’s
disease.
– The Human Genome Project proceeded through
several stages,
• During which preliminary maps were created and refined.
Genome-Mapping Techniques
– The whole-genome shotgun method
• Involves sequencing DNA fragments from an entire
genome and reassembling them in a single stage.
The Genetic Basis of Cancer
– In recent years, scientists have learned more about the
genetics of cancer.
– As early as 1911, certain viruses were known to
cause cancer.
– Cancer-causing viruses often carry specific genes
called oncogenes.
– Proto-oncogenes
• Are normal genes that can become oncogenes.
• Are found in many animals.
• Code for growth factors that stimulate cell division.
– For a proto-oncogene to become an oncogene, a
mutation must occur in the cell’s DNA.
– Tumor-suppressor genes
• Help prevent uncontrolled cell growth.
• May be mutated, and contribute to cancer.
Human Gene
Therapy
– Human gene therapy is a
recombinant DNA procedure
that seeks to treat disease by
altering the genes of the
afflicted person.
• The mutant version of a gene is
replaced or supplemented with
a properly functioning one.
Safety and Ethical Issues
– As soon as scientists realized the power of DNA
technology, they began to worry about potential
dangers such as:
• The creation of hazardous new pathogens
• The transfer of cancer genes into infectious bacteria and
viruses
– Strict laboratory safety procedures have been
designed to protect researchers from infection by
engineered microbes.
• Procedures have also been designed to prevent microbes
from accidentally leaving the laboratory.
The Controversy over
Genetically Modified Foods
– GM strains account for a significant percentage of
several agricultural crops in the United States.
– Advocates of a cautious approach have some
concerns:
• Crops carrying genes from other
species might harm the environment.
• GM foods could be hazardous to human
health.
• Transgenic plants might pass their genes
to close relatives in nearby wild areas.
– Negotiators from 130 countries (including the United
States) agreed on a Biosafety Protocol.
• The protocol requires exporters to identify GM organisms
present in bulk food shipments.
– Several U.S. regulatory agencies evaluate
biotechnology projects for potential risks:
•
•
•
•
Department of Agriculture
Food and Drug Administration
Environmental Protection Agency
National Institutes of Health
Ethical Questions Raised by
DNA Technology
– Should genetically engineered human growth
hormone be used to stimulate growth in HGHdeficient children?
– Genetic engineering of gametes and zygotes has been
accomplished in lab animals.
• Should we try to eliminate genetic defects in our children?
• Should we interfere with evolution in this way?
– Advances in genetic fingerprinting raise privacy
issues.
– What about the information obtained in the Human
Genome Project?
• How do we prevent genetic information from being used in
a discriminatory manner?
Evolution Connection:
Genomes Hold Clues to Evolution
– Genome data has confirmed evolutionary
connections,
• Such as between yeast cells and human cells.
– Comparisons of completed genome sequences
strongly support the theory that there are three
fundamental domains of life:
• Bacteria
• Archaea
• Eukaryotes
How and Why Genes Are Regulated
– Four of the many different types
of human cells:
• They all share the same
genome.
• What makes them different?
Gene Expression
• Genes are expressed as traits
• Traits are proteins or result from
reactions which are regulated by
proteins, such as enzymes.
• Genes are expressed through
protein synthesis.
Gene Regulation
How Does A Cell Know?
Which Gene To Express
&
Which Gene Should Stay Silent?
Patterns of Gene Expression in
Differentiated Cells
– In cellular differentiation:
• Certain genes are turned on and off.
• Cells become specialized in structure and function.
– In gene expression:
• A gene is turned on and transcribed into RNA.
• Information flows from genes to proteins, genotype to
phenotype.
– The regulation of gene expression plays a central role in
development from a zygote to a multi-cellular organism.
Gene Regulation
• When a Gene is Expressed:
– It is active and is Transcribed
into mRNA
• When a Gene is Silent:
– It is in active and is Not
Transcribed
Patterns of Gene Expression in
Specialized Human Cells
Vocabulary
• RNA polymerase: RNA polymerase (RNAP or
RNApol) is an enzyme that produces RNA.
• Repressor: inhibits transcription of structural
genes by binding to the operator
• Regulatory gene: codes for the repressor
Vocabulary
• Promoter: area on the DNA to which
the RNA polymerase attaches to begin
transcription
• Operator: area of the DNA to which
the repressor binds; “on/off” switch
• Structural genes: code for enzymes
which leads to a product
Gene Regulation
• Expression Regulated By
1. Promoters
• RNA Polymerase Binding Sites
• Certain DNA Base Pair Sequences
2. Start & Stop Base Pair Sequences
3. Regulatory Sites
• DNA Binding Proteins
• Regulate Transcription
Gene Regulation
Prokaryote Gene Regulation:
• What is an Operon?
• Group of Genes That Operate Together
• For Example:
– E. coli ferments (digests) lactose
• To Do That It Needs Three Enzymes
(Proteins), It Makes Them All At Once!
– 3 Genes Turned On & Off Together. This is
known as the lac Operon (lactose Operon)
Operons
• Operon: made of three parts
1. Operator
2. Promoter
3. Group of genes
–
located together which
express proteins for a similar
function.
Two type of operons
1. Inducible
– Example: lac operon
•
Lac = lactose
– Normally off but can be activated
2. Repressible
– Example: trp operon
•
Trp = tryptophan
– Normally on but can be inhibited
Gene Regulation: lac Operon
The lac Operon
–
–
Regulates Lactose Metabolism
It Turns On Only When Lactose Is Present &
Glucose is Absent.
Lactose is a Disaccharide
–
A Combination of Galactose & Glucose
To Ferment Lactose E. coli Must:
1. Transport Lactose Across Cell Membrane
2. Separate The Two Sugars
Gene Regulation: lac Operon
Each Task Requires A Specific Protein
but
Proteins Not Needed If Glucose Present
(why waste energy if you already have food?)
so
Genes Coding For Proteins Expressed Only
When There Is No Glucose Present But
Lactose Is Present
Gene Regulation: lac Operon
Gene Regulation: lac Operon
ADD LACTOSE
= Lactose
Gene Regulation: lac Operon
Gene Regulation: lac Operon
Key Concept:
The lac Genes Are:
Turned Off By Repressors
And
Turned On By The Presence Of
Lactose
lac Gene Expression
• Operon Has 2
Regulatory Regions
1. Promoter (RNA
Polymerase Binding)
2. Operator (O region)
Bound To A lac
Repressor
lac Gene Expression
• lac Repressor
– When Bound To O
Region : Prevents
Binding of RNA
Polymerase To
Promoter
– Turns The Operon
“OFF”
lac Gene Expression
• lac Repressor Also Binds
To Lactose
– Higher Affinity For
Lactose
• When Lactose Present lac
Repressor Is Released
From O Region
– Allows Transcription of
All Three Genes
Compare and Contrast
Regulation Can Be:
1. Based On Repressors
2. Based On Enhancers
3. Regulated At Protein Synthesis
Eukaryotic Gene Regulation
Operons Usually
NOT Found In Eukaryotes
Key Concept:
Most Eukaryotic Genes Are Controlled
Individually And Have Regulatory
Sequences That Are Much More
Complex Than Prokaryotic Gene
Regulation
Eukaryotic Gene Regulation
Eukaryotic Gene Regulation
• TATA Box
– About 30 Base Pairs Long
– Found Before Most Genes
– Positions RNA Polymerase
– Usually TATATA or TATAAA
– Promoters Usually Occur Just Before
The TATA Box
Eukaryotic Promoters
Enhancer Sequences
– Series of Short DNA Sequences
– Many Types
Enormous Number Of Proteins Can Bind
To Enhancer Sequences
– Makes Eukaryote Enhancement Very
Complex
Eukaryotic Promotors
• Some Enhance Transcription By Opening
Up Packed Chromatin
• Others Attract RNA Polymerase
• Some Block Access To Genes
• Key To Cell Specialization
– All Cells Have Same Chromosomes
– Some Liver, Skin, Muscle, etc.
The End