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Biology
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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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12–1 DNA
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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12–1 DNA
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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12–1 DNA
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.
This factor could transfer information from the
disease causing bacteria even though they were
dead.
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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.
What was not destroyed?
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12–1 DNA
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
What did scientists discover about the
relationship between genes and DNA?
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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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12–1 DNA
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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12–1 DNA
The Hershey-Chase Experiment
When a bacteriophage enters a bacterium, the
virus attaches to the surface of the cell and injects
its genetic information into it.
The viral genes produce many new
bacteriophages, which eventually destroy the
bacterium.
When the cell splits open, hundreds of new viruses
burst out.
Think “Aliens”
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12–1 DNA
The Hershey-Chase Experiment
If Hershey and Chase could determine which part
of the virus entered an infected cell, they would
learn whether genes were made of protein or DNA.
They grew viruses in cultures containing
radioactive isotopes of phosphorus-32 (32P) and
sulfur-35 (35S).
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12–1 DNA
The Hershey-Chase Experiment
If 35S was found in the bacteria, it would mean that
the viruses’ protein had been injected into the
bacteria. (Some protein contains sulfur)
Bacteriophage with
suffur-35 in protein coat
Phage infects
bacterium
No radioactivity
inside bacterium
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12–1 DNA
The Hershey-Chase Experiment
If 32P was found in the bacteria, then it was the DNA
that had been injected. (DNA contains Phosphorous)
Bacteriophage with
phosphorus-32 in DNA
Phage infects
bacterium
Radioactivity
inside bacterium
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12–1 DNA
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
What is the overall structure of the DNA
molecule?
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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 a five-carbon sugar called deoxyribose, a
phosphate group, and a 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
The backbone of a DNA chain is formed by sugar
and phosphate groups of each nucleotide.
The nucleotides can be joined together in any order.
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12–1 DNA
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.
HUMMMMMM……..?
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12–1 DNA
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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DNA
The Double12–1
Helix
The Components and Structure of DNA
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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12–1 DNA
The Components and Structure of
DNA
DNA Double Helix
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12–1 DNA
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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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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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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DNA is a long molecule made of monomers
called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.
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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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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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END OF SECTION
Biology
Biology
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12–2 Chromosomes and DNA
Replication
12-2 Chromosomes and DNA Replication
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DNA and Chromosomes
12–2 Chromosomes
and
DNA Replication
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 Chromosomes
12–2 Chromosomes
and
DNA Replication
Chromosome
E. Coli Bacterium
Bases on the
Chromosomes
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DNA and Chromosomes
12–2 Chromosomes
and
DNA Replication
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.
Fruit fly
Human
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DNA and Chromosomes
12–2 Chromosomes
and
DNA Replication
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 Chromosomes
12–2 Chromosomes
and
DNA Replication
Eukaryotic Chromosome Structure
Chromosome Nucleosome
Coils
Supercoils
DNA
doub
le
helix
Histones
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DNA Replication
12–2 Chromosomes
and
DNA Replication
What happens during DNA replication?
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DNA Replication
12–2 Chromosomes
and
DNA Replication
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 Replication
12–2 Chromosomes
and
DNA Replication
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 Replication
12–2 Chromosomes
and
DNA Replication
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 Replication
12–2 Chromosomes
and
DNA Replication
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 Replication
12–2 Chromosomes
and
DNA Replication
New
Original
Strand
strand
Nitrogen
Bases
Grow
Grow
th
th
Replication
Fork
Replication
Fork
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DNA
Polymeras
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DNA Replication
12–2 Chromosomes
and
DNA Replication
How 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 Replication
12–2 Chromosomes
and
DNA Replication
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.
DNA Replication video:
http://www.youtube.com/watch?v=teV62zrm2P0
Simplified:
http://www.youtube.com/watch?v=hfZ8o9D1tus&feat
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12–2
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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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END OF SECTION