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Biology
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12–1 DNA
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12–1 DNA
Griffith and Transformation
Griffith and Transformation
In 1928, British scientist Fredrick Griffith was
trying to learn how certain types of bacteria caused
pneumonia.
He isolated two different strains of pneumonia
bacteria from mice and grew them in his lab.
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Griffith and Transformation
Griffith made two observations:
(1) The disease-causing strain of bacteria grew
into smooth colonies on culture plates.
(2) The harmless strain grew into colonies with
rough edges.
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12–1 DNA
Griffith and Transformation
Griffith's Experiments
Griffith set up four
individual experiments.
Experiment 1: Mice
were injected with the
disease-causing strain
of bacteria. The mice
developed pneumonia
and died.
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12–1 DNA
Griffith and Transformation
Experiment 2: Mice were
injected with the harmless
strain of bacteria. These
mice didn’t get sick.
Harmless bacteria
(rough colonies)
Lives
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Griffith and Transformation
Experiment 3: Griffith
heated the diseasecausing bacteria. He then
injected the heat-killed
bacteria into the mice.
The mice survived.
Heat-killed diseasecausing bacteria (smooth
colonies)
Lives
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Griffith and Transformation
Experiment 4: Griffith
mixed his heat-killed,
disease-causing bacteria
with live, harmless
bacteria and injected the
mixture into the mice.
The mice developed
pneumonia and died.
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Live diseasecausing bacteria
(smooth colonies)
Dies of pneumonia
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12–1 DNA
Griffith and Transformation
Griffith concluded that
the heat-killed bacteria
passed their diseasecausing ability to the
harmless strain.
Heat-killed diseasecausing bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Live diseasecausing bacteria
(smooth colonies)
Dies of pneumonia
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Griffith and Transformation
Transformation
Griffith called this process transformation
because one strain of bacteria (the harmless strain)
had changed permanently into another (the
disease-causing strain).
Griffith hypothesized that a factor must contain
information that could change harmless bacteria
into disease-causing ones.
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Avery and DNA
Avery and DNA
Oswald Avery repeated Griffith’s work to determine
which molecule was most important for
transformation.
Avery and his colleagues made an extract from the
heat-killed bacteria that they treated with enzymes.
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12–1 DNA
Avery and DNA
The enzymes destroyed proteins, lipids,
carbohydrates, and other molecules, including the
nucleic acid RNA.
Transformation still occurred.
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Avery and DNA
Avery and other scientists repeated the experiment
using enzymes that would break down DNA.
When DNA was destroyed, transformation did not
occur. Therefore, they concluded that DNA was the
transforming factor.
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12–1 DNA
Avery and DNA
Avery and other scientists discovered
that the nucleic acid DNA stores and
transmits the genetic information from
one generation of an organism to the
next.
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The Hershey-Chase Experiment
The Hershey-Chase Experiment
Alfred Hershey and Martha Chase studied
viruses—nonliving particles smaller than a cell that
can infect living organisms.
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The Hershey-Chase Experiment
Bacteriophages
A virus that infects bacteria is known as a
bacteriophage.
Bacteriophages are composed of a DNA or RNA
core and a protein coat.
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The Hershey-Chase Experiment
They grew viruses in cultures containing
radioactive isotopes of phosphorus-32 (32P) and
sulfur-35 (35S).
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The Hershey-Chase Experiment
If 35S was found in the bacteria, it would mean that
the viruses’ protein had been injected into the
bacteria.
Bacteriophage with
suffur-35 in protein coat
Phage infects
bacterium
No radioactivity
inside bacterium
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The Hershey-Chase Experiment
If 32P was found in the bacteria, then it was the DNA
that had been injected.
Bacteriophage with
phosphorus-32 in DNA
Phage infects
bacterium
Radioactivity
inside bacterium
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The Hershey-Chase Experiment
Nearly all the radioactivity in the bacteria
was from phosphorus (32P).
Hershey and Chase concluded that the
genetic material of the bacteriophage
was DNA, not protein.
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12–1 DNA
The Components and Structure of DNA
The Components and Structure of DNA
DNA is made up of nucleotides.
A nucleotide is a monomer of nucleic acids made
up of:
•Deoxyribose – 5-carbon Sugar
•Phosphate Group
•Nitrogenous Base
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12–1 DNA
The Structure
of DNA
• DNA is a long Molecule
of repeating
nucleotides
• Each nucleotide has 3
parts:
– 5 Carbon Sugar
(Deoxyribose)
– 1 Phosphate Group
– 1 Nitrogenous Base
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The Components and Structure of DNA
There are four
kinds of bases in
in DNA:
• adenine
• guanine
• cytosine
• thymine
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12–1 DNA
Purines
Pyrimidines
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The Components and Structure of DNA
Chargaff's Rules
Erwin Chargaff discovered that:
• The percentages of guanine [G] and cytosine
[C] bases are almost equal in any sample of
DNA.
• The percentages of adenine [A] and thymine
[T] bases are almost equal in any sample of
DNA.
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The Components and Structure of DNA
X-Ray Evidence
Rosalind Franklin used X-ray
diffraction to get information
about the structure of DNA.
She aimed an X-ray beam at
concentrated DNA samples
and recorded the scattering
pattern of the X-rays on film.
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The Components and Structure of DNA
The Double Helix
Using clues from Franklin’s pattern, James
Watson and Francis Crick built a model that
explained how DNA carried information and
could be copied.
Watson and Crick's model of DNA was a
double helix, in which two strands were
wound around each other.
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The Components and Structure of
DNA
DNA Double Helix
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The Components and Structure of
DNA
Watson and Crick discovered that hydrogen bonds
can form only between certain base pairs—
adenine and thymine,
guanine and cytosine.
This principle is called base pairing.
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Chapter 12
DNA & RNA
Section 12-2
Chromosomes &
DNA Replication
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Objectives
• What happens during DNA
replication?
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DNA & Chromosomes
• DNA Location
–Prokaryotes – Cytoplasm
•
Single Circular Molecule
–Eukaryotes – Nucleus
•
•
•
•
Multiple Chromosomes
Humans 46
Drosophila 8
Giant Sequoia 22
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DNA Length
• E. coli (Gram Neg.
Bacilli)
4,639,221 Base Pairs
1.6 mm long which
must fit in a bacteria 1.6
um wide, or 1/1000 the
length of the DNA
strand
• Human DNA 1000 times
larger
• Tightly Packed
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Chromosome Structure
Each Human Cell Contains More Than A
6 feet of DNA
• Tightly Packed Into Chromatin
DNA + Protein = Chromatin
DNA Coiled Around Proteins Called Histones
•
Forms Beads Called Nucleosomes
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Chromosome Structure
• Nucleosomes pack together to form a
thick fiber containing loops and curls
Usually loose, diffuse
Condense during Mitosis & Meiosis
Fold enormous lengths of DNA into the tiny
nucleus
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Chromosome Structure
Histones
proteins that have very
low mutation rates
Appears most
mutations have been
lethal – therefore,
eliminated
Regulate “reading” of
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DNA Replication
• Watson & Crick Discovered
–Structure of DNA
–How DNA can be copied and
replicated.
–Each strand of DNA is a mirror
image of the other strand
•
Strands are Complimentary
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Duplicating DNA
Replication
Duplication of the DNA in preparation for cell
division ( S phase of Interphase )
Prokaryotes
Replication starts at a single point and proceeds in
opposite directions
Eukaryotes
Occurs at multiple points on multiple chromosomes at
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Duplicating DNA
Key Concept:
During DNA replication, the DNA
molecule separates into two
strands, then produces two new
complementary strands following
the rules of base pairing. Each
strand of the double helix of DNA
serves as a template, or model, for
the new strand
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How Replication Occurs
Carried out by enzymes
1) They unzip the molecule of DNA
Break the hydrogen bonds between the base
pairs
2) Each strand is a template for the
new strand
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DNA Replication
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How Replication Occurs
• Original DNA
TACGTT
ATGCAA
• Unzipped
TACGTT
ATGCAA
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How Replication Occurs
Replicated:
TACGTT
ATGCAA
ATGCAA
TACGTT
Remember – Base Pairing
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How Replication Occurs
Enzymes Involved Named For The
Reactions They Catalyze
DNA Polymerase
1) Polymerizes individual nucleotides
2) Proof Reads each new DNA strand
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DNA Polymerase
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http://207.207.4.198/pub/flash/24/menu.swf
http://www.lewport.wnyric.org/JWAN
AMAKER/animations/DNA%20Replic
ation%20-%20long%20.html
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Chapter 12
DNA & RNA
Section 12-3
RNA & Protein Synthesis
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Objectives
• What are the three main types of
RNA?
• What is transcription?
• What is translation?
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The Structure of RNA
• Long Chains of Nucleotides
–5 Carbon Sugar ( Ribose )
–Phosphate Group
–Nitrogenous Base
•
A, G, C, U ( no T )
–Single Stranded
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RNA Mostly For Protein Synthesis
Types of RNA
Three Types of RNA
Messenger RNA, mRNA
Ribosomal RNA, rRNA
Transfer RNA,
tRNA
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Types of RNA
mRNA
Template to construct protein from
the DNA to the ribosome.
rRNA
Part of ribosome structure
tRNA
Transports amino acids from cytoplasm to the51 Slide
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ribosomes
Transcription
The process of copying part of the
DNA nucleotide sequence into a
complementary sequence of RNA
Requires enzymes e.g. RNA
Polymerase
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RNA Polymerase
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Transcription
Key Concept:
During transcription, RNA
polymerase binds to DNA and
separates the DNA strands. RNA
Polymerase then uses one strand
of DNA as a template to assemble
nucleotides into RNA
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Transcription
Promoters
–Regions on DNA that show where RNA
Polymerase must bind to begin the
Transcription of RNA
–Specific base sequences act as signals
–Other base sequences indicate stopping
points
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Transcription
RNA Splicing
–After the DNA is transcribed into RNA
editing must be done to the nucleotide chain
to make the RNA functional
–Introns
• Snipped out of the chain in the nucleus, nonfunctional segments
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mRNA Splicing
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RNA Splicing
Exons
Remaining, active segments of
nucleotides
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The Genetic Code
Proteins are long chains of amino
acids.
There are 20 different amino acids
The order of amino acids in the
protein determine its shape and
function
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The Genetic Code
There are 20 amino acids but only
4 bases in RNA
Adenine
A
Cytosine
C
Guanine
G
Uracil
U
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The Genetic Code
The genetic code consists of
“words” three bases long
Each “word” is called a Codon:
three consecutive nucleotides that
specifies a single amino acid
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The Genetic Code
For Example:
UCGCACGGU = RNA Sequence
UCG-CAC-GGU = Codons
UCG codes for Serine
CAC codes for Histidine
GGU codes for Glycine
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Code Wheel
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The Genetic Code
4 Bases
Codons Defined with 3 Bases
There Are 64 Possible
3-base codons
Since there are only 20 amino acids,
some amino acids are represented
by multiple codons
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Translation
Translation is the process of of
decoding the mRNA into a polypeptide
chain
• Ribosomes
–Read mRNA and construct the
proteins
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Translation Step A
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Translation Step B
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Translation
Step C
–Ribosome connects the
amino acids together as they
come into the ribosome
–Ribosome disconnects the
the 3rd amino acid from the
ribosome to float into the
cytoplasm
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Translation
• Step D
–Polypeptide chain
grows until the
mRNA STOP Codon
is reached
–The ribosome then
releases the
polypeptide chain
into the cytoplasm
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The Roles of RNA & DNA
DNA =
Master Plan
RNA =
Blueprints of the Master Plan
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Genes & Proteins
• Genes are instruction for assembling
proteins
• Proteins are enzymes that catalyze and
regulate chemical reactions
–Pigments, antigens, regulators
–Proteins are keys to function
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• http://www.lewport.wnyric.org/JWANAMAKER/ani
mations/Protein%20Synthesis%20-%20long.html
• http://207.207.4.198/pub/flash/26/transmenu_s.swf
• http://www.biostudio.com/demo_freeman_protein_
synthesis.htm
• http://www.wisconline.com/objects/index_tj.asp?objID=AP1302
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Chapter 12
DNA & RNA
Section 12 – 4
Mutations
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Objectives
• What are mutations?
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Mutations
Key Concept:
Gene mutations result from
changes in a single gene.
Chromosomal mutations
involve changes in whole
chromosomes
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Gene Mutations
• Point Mutations
– Affect one nucleotide
– Occur at a single point in the gene
sequence
– Three Types:
1.Deletion
2.Insertion
3.Substitution
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Point Mutations
Frameshift Mutations
Result From
Insertions & Deletions
A nucleotide is added, or subtracted
from the nucleotide sequence. This
shifts the Codon grouping and
drastically alters the amino acid
sequence in the protein.
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Point Mutations
Substitution
A single nucleotide is changed in the
nucleotide sequence.
• This may result in a change to a single
amino acid in the protein.
• The change to a single amino acid may
or may not alter the proteins function.
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Point Mutations - Substitution
Codon
=
Amino Acid
UGU
UGC
UGG
UGA
Original
Cysteine
No
Change
Cysteine
Single
AA
Tryptophan
Bad
STOP
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Chromosomal Mutations
• Changes the number or structure
of chromosomes
• May change locations of genes on
chromosome or the number of
copies of some genes
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Chromosomal Mutations
4 Types
1. Deletion
2. Duplication
3. Inversion
4. Translocation
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Deletion
X
Deletion
Loss of all or part of a
chromosome
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Duplication
Duplication
Segment of chromosome is
repeated
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Inversion
Inversion
Chromosome or part of a
chromosome is oriented in the
reverse direction
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Translocation
Translocation
Part of one chromosome breaks
off and attaches to another,
nonhomologous chromosome
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Chapter 12
DNA & RNA
Section 12 – 5
Gene Regulation
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Objectives
• How are lac genes turned off and
on?
• How are most eukaryotic genes
controlled?
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Gene Regulation
How Does A Cell Know?
Which Gene To Express
&
Which Gene Should Stay
Silent?
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Gene Regulation
• When a Gene is
Expressed:
–It Is Transcribed Into mRNA
• When a Gene is Silent:
–It Is Not Transcribed
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Gene Regulation
• Expression Regulated By
–Promoters
•
RNA Polymerase Binding Sites
•
Certain DNA Base Pair Sequences
–Start & Stop Base Pair Sequences
–Regulatory Sites
•
•
DNA Binding Proteins
Regulate Transcription
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Gene Regulation
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Gene Regulation: lac Operon
• What is an Operon?
•
Group of Genes That Operate Together
• For Example:
–E. coli ferments 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
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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
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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
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Gene Regulation: lac Operon
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Gene Regulation: lac Operon
ADD LACTOSE
= Lactose
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Gene Regulation: lac Operon
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Gene Regulation: lac Operon
Key Concept:
The lac Genes Are:
Turned Off By Repressors
And
Turned On By The Presence Of
Lactose
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lac Gene Expression
• Operon Has 2
Regulatory
Regions
–Promoter (RNA
Polymerase Binding)
–Operator (O region)
Bound To A lac
Repressor
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lac Gene Expression
• lac Repressor
–When Bound
To O Region :
Prevents
Binding of RNA
Polymerase To
Promoter
–Turns The
Operon “OFF”
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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
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Regulation Can Be:
1. Based On Repressors
2. Based On Enhancers
3. Regulated At Protein Synthesis
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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
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Eukaryotic Gene Regulation
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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
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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
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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.
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Regulation & Development
• hox Genes
–Control Organ & Tissue Development In
The Embryo
–Mutations Lead To Major Changes
•
Drosophila With Legs In Place of Antennae
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Regulation & Development
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Regulation & Development
hox Genes Present In All Eukaryotes
–Shows Common Ancestry
–Pax 6 hox gene
•
Controls eye growth in Drosophila, Mice & Man
• Pax 6 from Mouse Placed In Knee Development
Sequence Of Drosophila Developed Into Eye
Tissue.
Common Ancestor >600M Years Ago
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Regulation & Development
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