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12–1 DNA
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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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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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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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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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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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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
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No radioactivity
inside bacterium
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
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Radioactivity
inside bacterium
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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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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The Components and Structure of DNA
There are four
kinds of bases in
in DNA:
• adenine
• guanine
• cytosine
• thymine
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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, and guanine and cytosine.
This principle is called base pairing.
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12–1
Avery and other scientists discovered that
a. DNA is found in a protein coat.
b. DNA stores and transmits genetic
information from one generation to the next.
c. transformation does not affect bacteria.
d. proteins transmit genetic information from
one generation to the next.
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12–1
The Hershey-Chase experiment was based on
the fact that
a. DNA has both sulfur and phosphorus in its
structure.
b. protein has both sulfur and phosphorus in
its structure.
c. both DNA and protein have no phosphorus
or sulfur in their structure.
d. DNA has only phosphorus, while protein
has only sulfur in its structure.
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12–1
DNA is a long molecule made of monomers
called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.
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12–1
Chargaff's rules state that the number of
guanine nucleotides must equal the number of
a. cytosine nucleotides.
b. adenine nucleotides.
c. thymine nucleotides.
d. thymine plus adenine nucleotides.
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12–1
In DNA, the following base pairs occur:
a. A with C, and G with T.
b. A with T, and C with G.
c. A with G, and C with T.
d. A with T, and C with T.
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12–2 Chromosomes
and DNA Replication
12-2 Chromosomes and DNA Replication
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DNA
and
Chromo
somes
DNA and Chromosomes
In prokaryotic cells, DNA is located in the
cytoplasm.
Most prokaryotes have a single DNA molecule
containing nearly all of the cell’s genetic
information.
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DNA
and
Chromo
somes
Chromosome
E. Coli Bacterium
Bases on the
Chromosomes
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DNA
and
Chromo
somes
Many eukaryotes have 1000 times the
amount of DNA as prokaryotes.
Eukaryotic DNA is located in the cell
nucleus inside chromosomes.
The number of chromosomes varies
widely from one species to the next.
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DNA
and
Chromo
somes
Chromosome Structure
Eukaryotic chromosomes contain DNA and
protein, tightly packed together to form
chromatin.
Chromatin consists of DNA tightly coiled around
proteins called histones.
DNA and histone molecules form nucleosomes.
Nucleosomes pack together, forming a thick
fiber.
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DNA
and
Chromo
somes
Eukaryotic Chromosome Structure
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
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DNA
Replica
tion
DNA Replication
Each strand of the DNA double helix has all
the information needed to reconstruct the
other half by the mechanism of base pairing.
In most prokaryotes, DNA replication begins
at a single point and continues in two
directions.
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DNA
Replica
tion
In eukaryotic chromosomes, DNA
replication occurs at hundreds of places.
Replication proceeds in both directions
until each chromosome is completely
copied.
The sites where separation and replication
occur are called replication forks.
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DNA
Replica
tion
Duplicating DNA
Before a cell divides, it duplicates its DNA in a
process called replication.
Replication ensures that each resulting cell will
have a complete set of DNA.
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DNA
Replica
tion
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 for the new
strand.
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DNA
Replica
tion
New Strand
Original strand
Nitrogen Bases
Growth
Growth
Replication Fork
Replication Fork
DNA Polymerase
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DNA
Replica
tionHow
Replication Occurs
DNA replication is carried out by enzymes that
“unzip” a molecule of DNA.
Hydrogen bonds between base pairs are
broken and the two strands of DNA unwind.
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DNA
Replica
tion
New Strand
Original strand
Nitrogen Bases
Growth
Growth
Replication Fork
Replication Fork
DNA Polymerase
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DNA
Replica
tion
The principal enzyme involved in DNA
replication is DNA polymerase.
DNA polymerase joins individual
nucleotides to produce a DNA molecule
and then “proofreads” each new DNA
strand.
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12–2
In prokaryotic cells, DNA is found in the
a. cytoplasm.
b. nucleus.
c. ribosome.
d. cell membrane.
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12–2
The first step in DNA replication is
a. producing two new strands.
b. separating the strands.
c. producing DNA polymerase.
d. correctly pairing bases.
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12–2
A DNA molecule separates, and the sequence
GCGAATTCG occurs in one strand. What is the
base sequence on the other strand?
a. GCGAATTCG
b. CGCTTAAGC
c. TATCCGGAT
d. GATGGCCAG
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12–2
In addition to carrying out the replication of DNA,
the enzyme DNA polymerase also functions to
a. unzip the DNA molecule.
b. regulate the time copying occurs in the cell
cycle.
c. “proofread” the new copies to minimize the
number of mistakes.
d. wrap the new strands onto histone proteins.
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12–2
The structure that may play a role in regulating
how genes are “read” to make a protein is the
a. coil.
b. histone.
c. nucleosome.
d. chromatin.
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12-3 RNA and Protein Synthe
12–3 RNA and Protein Synthesis
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and
Protein
Synthe
sis
Genes are coded DNA instructions that
control the production of proteins.
Genetic messages can be decoded by
copying part of the nucleotide sequence
from DNA into RNA.
RNA contains coded information for
making proteins.
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The
Structu
re of
RNA
The Structure of RNA
There are three main differences between RNA and DNA:
a. The sugar in RNA is ribose instead of
deoxyribose.
b. RNA is generally single-stranded.
c. RNA contains uracil in place of thymine.
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Types
of RNA
Types of RNA
There are three main types of RNA:
a. messenger RNA
b. ribosomal RNA
c. transfer RNA
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Types
of RNA
Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids
into proteins.
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Types
of RNA
Ribosome
Ribosomal RNA
Ribosomes are made up of proteins and
ribosomal RNA (rRNA).
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Protein
Synthe
sis
DNA
molecule
DNA strand
(template)
5
3
TRANSCRIPTION
mRNA
5
3
Codon
TRANSLATION
Protein
Amino acid
Transcr
iption
Transcription
DNA is copied in the form of
RNA
This first process is called
transcription.
The process begins at a section
of DNA called a promoter.
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Transcr
iption
RNA
RNA polymerase
DNA
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RNA
Editing
RNA Editing
Some DNA within a gene is not needed to
produce a protein. These areas are called
introns.
The DNA sequences that code for proteins are
called exons.
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RNA
Editing
The introns are
cut out of RNA
molecules.
Exon Intron
DNA
Pre-mRNA
The exons are the
spliced together
to form mRNA.
mRNA
Cap
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Tail
The
Genetic
Code
The Genetic Code
The genetic code is the “language” of mRNA
instructions.
The code is written using four “letters” (the
bases: A, U, C, and G).
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The
Genetic
Code
A codon consists of three consecutive
nucleotides on mRNA that specify a
particular amino acid.
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The
Genetic
Code
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Transla
tion
Translation
Translation is the decoding of an mRNA
message into a polypeptide chain (protein).
Translation takes place on ribosomes.
During translation, the cell uses information from
messenger RNA to produce proteins.
Nucleus
mRNA
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Transla
tion
The ribosome binds new tRNA molecules
and amino acids as it moves along the
Lysine
mRNA.Phenylalanine
tRNA
Methionine
Ribosome
mRNA
Start codon
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Transla
tion
Protein Synthesis
Lysine
tRNA
Translation direction
mRNA
Ribosome
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Transla
tion
The process continues until the ribosome
reaches a stop codon.
Polypeptide
Ribosome
tRNA
mRNA
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Genes
and
Protein
s
Codon
Codon Codon
DNA
Single strand of DNA
Codon Codon Codon
mRNA
mRNA
Alanine Arginine Leucine
Protein
Amino acids within
a polypeptide
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12–3
The role of a master plan in a building is similar
to the role of which molecule?
a. messenger RNA
b. DNA
c. transfer RNA
d. ribosomal RNA
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12–3
A base that is present in RNA but NOT in DNA is
a. thymine.
b. uracil.
c. cytosine.
d. adenine.
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12–3
The nucleic acid responsible for bringing
individual amino acids to the ribosome is
a. transfer RNA.
b. DNA.
c. messenger RNA.
d. ribosomal RNA.
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12–3
A region of a DNA molecule that indicates to an
enzyme where to bind to make RNA is the
a. intron.
b. exon.
c. promoter.
d. codon.
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12–3
A codon typically carries sufficient information to
specify a(an)
a. single base pair in RNA.
b. single amino acid.
c. entire protein.
d. single base pair in DNA.
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12–4 Mutations
12-4 Mutations
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124 Mutati
ons
Mutations are changes in the genetic material.
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Kinds of Mutations
Kinds of Mutations
Mutations that produce changes in a single
gene are known as gene mutations.
Mutations that produce changes in whole
chromosomes are known as chromosomal
mutations.
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Kinds of Mutations
Gene Mutations
Gene mutations involving a change in one or
a few nucleotides are known as point
mutations because they occur at a single
point in the DNA sequence.
Point mutations include substitutions,
insertions, and deletions.
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Kinds of Mutations
Substitutions
usually affect
no more than a
single amino
acid.
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Kinds of Mutations
The effects of insertions or deletions are
more dramatic.
The addition or deletion of a nucleotide
causes a shift in the grouping of codons.
Changes like these are called frameshift
mutations.
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Kinds of Mutations
In an insertion, an
extra base is
inserted into a
base sequence.
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Kinds of Mutations
In a deletion, the loss of a single base is
deleted and the reading frame is shifted.
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Kinds of Mutations
Chromosomal Mutations
Chromosomal mutations involve changes in the
number or structure of chromosomes.
Chromosomal mutations include deletions,
duplications, inversions, and translocations.
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Kinds of Mutations
Deletions involve the loss of all or part of a
chromosome.
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Kinds of Mutations
Duplications produce extra copies of parts of
a chromosome.
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Kinds of Mutations
Inversions reverse the direction of parts of
chromosomes.
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Kinds of Mutations
Translocations occurs when part of one
chromosome breaks off and attaches to another.
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Significance of Mutations
Significance of Mutations
Many mutations have little or no effect on gene
expression.
Some mutations are the cause of genetic
disorders.
Polyploidy is the condition in which an
organism has extra sets of chromosomes.
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12–4
A mutation in which all or part of a chromosome
is lost is called a(an)
a. duplication.
b. deletion.
c. inversion.
d. point mutation.
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12–4
A mutation that affects every amino acid
following an insertion or deletion is called a(an)
a. frameshift mutation.
b. point mutation.
c. chromosomal mutation.
d. inversion.
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12–4
A mutation in which a segment of a chromosome
is repeated is called a(an)
a. deletion.
b. inversion.
c. duplication.
d. point mutation.
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12–4
The type of point mutation that usually affects
only a single amino acid is called
a. a deletion.
b. a frameshift mutation.
c. an insertion.
d. a substitution.
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12–4
When two different chromosomes exchange
some of their material, the mutation is called
a(an)
a. inversion.
b. deletion.
c. substitution.
d. translocation.
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• 12-5 Gene Regulation
Fruit fly chromosome Mouse chromosomes
12-5 Gene Regulation
Fruit fly embryo
Mouse embryo
Adult fruit fly
Adult mouse
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Gene Regulation: An
Example
• Gene Regulation: An Example
a. E. coli provides an example of how gene
expression can be regulated.
b. An operon is a group of genes that operate
together.
c. In E. coli, these genes must be turned on so
the bacterium can use lactose as food.
d. Therefore, they are called the lac operon.
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Gene Regulation: An
Example
–How are lac genes turned off and on?
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Gene Regulation: An
Example
–The lac genes are turned off by repressors and
turned on by the presence of lactose.
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Gene Regulation: An
Example
–On one side of the operon's three genes are two
regulatory regions.
a. In the promoter (P) region, RNA polymerase
binds and then begins transcription.
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Gene Regulation: An
Example
a. The other region is the operator (O).
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Gene Regulation: An
Example
–When the lac repressor binds to the O region,
transcription is not possible.
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Gene Regulation: An
Example
• When lactose is added, sugar binds to the
repressor proteins.
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Gene Regulation: An
Example
• The repressor protein changes shape and falls off
the operator and transcription is made possible.
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Gene Regulation: An
Example
• Many genes are regulated by repressor
proteins.
• Some genes use proteins that speed
transcription.
• Sometimes regulation occurs at the level
of protein synthesis.
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Eukaryotic Gene Regulation
–How are most eukaryotic genes controlled?
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Eukaryotic Gene Regulation
• Eukaryotic Gene Regulation
–Operons are generally not found in
eukaryotes.
–Most eukaryotic genes are controlled
individually and have regulatory sequences that
are much more complex than those of the lac
operon.
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Eukaryotic Gene Regulation
• Many eukaryotic genes have a sequence called
the TATA box.
Upstream
enhancer
TATA
box
Introns
Promoter
sequences
Exons
Direction of transcription
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Eukaryotic Gene Regulation
• The TATA box seems to help position RNA
polymerase.
Upstream
enhancer
TATA
box
Introns
Promoter
sequences
Exons
Direction of transcription
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Eukaryotic Gene Regulation
• Eukaryotic promoters are usually found just before
the TATA box, and consist of short DNA
sequences.
Upstream
enhancer
TATA
box
Introns
Promoter
sequences
Exons
Direction of transcription
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Eukaryotic Gene Regulation
• Genes are regulated in a variety of ways by
enhancer sequences.
• Many proteins can bind to different enhancer
sequences.
• Some DNA-binding proteins enhance transcription
by:
a. opening up tightly packed chromatin
b. helping to attract RNA polymerase
c. blocking access to genes.
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Development and
Differentiation
• Development and Differentiation
a. As cells grow and divide, they undergo
differentiation, meaning they become
specialized in structure and function.
b. Hox genes control the differentiation of cells
and tissues in the embryo.
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Development and
Differentiation
• Careful control of expression in hox
genes is essential for normal
development.
• All hox genes are descended from the
genes of common ancestors.
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Development and
Differentiation
• Hox Genes
Fruit fly chromosome Mouse chromosomes
Fruit fly embryo
Mouse embryo
Adult fruit fly
Adult mouse
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12–5
–Which sequence shows the typical organization
of a single gene site on a DNA strand?
a. start codon, regulatory site, promoter, stop
codon
b. regulatory site, promoter, start codon, stop
codon
c. start codon, promoter, regulatory site, stop
codon
d. promoter, regulatory site, start codon, stop
codon
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12–5
– A group of genes that operates together is
a(an)
a. promoter.
b. operon.
c. operator.
d. intron.
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12–5
– Repressors function to
a. turn genes off.
b. produce lactose.
c. turn genes on.
d. slow cell division.
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12–5
–Which of the following is unique to the
regulation of eukaryotic genes?
a. promoter sequences
b. TATA box
c. different start codons
d. regulatory proteins
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12–5
–Organs and tissues that develop in various
parts of embryos are controlled by
a. regulation sites.
b. RNA polymerase.
c. hox genes.
d. DNA polymerase.
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