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Chapter 12 Notes - DNA and RNA
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12–1 DNA
A. Griffith and Transformation
1. Griffith’s Experiments
2. Transformation
B. Avery and DNA
C. The Hershey-Chase Experiment
1. Bacteriophages
2. Radioactive Markers
D. The Components and Structure of
DNA
1. Chargaff’s Rules
2. X-Ray Evidence
3. The Double Helix
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Name_______________
Date _______ Period __
What is DNA?
Although the environment influences how an organism develops, the genetic
information that is held in the molecules of DNA ultimately determines an
organism’s _____________.
DNA achieves its control by determining the structure of ________________.
All actions, such as eating, running, and even thinking, depend on proteins called
enzymes.
Enzymes are critical for an organism’s function because they control the chemical
reactions needed for life.
Within the structure of DNA is the information for life—the complete instructions for
manufacturing all the _______________ for an organism.
How Replication
Occurs
 2.Many
scientists
have contributed to our current knowledge of DNA.
 ________________ studied material in nucleus and found it to be half protein and half DNA in 1868.
 In the 1900’s, Walter Sutton and Thomas Hunt Morgan showed that genes are the units of heredity and are
located on _____________________
Griffith’s Experiment
 In 1928, Frederick Griffith conducted an experiment in
which he was studying how pneumonia causing
bacteria made people sick.
 Griffith injected ______ with four different samples of
bacteria from the smooth and rough colonies.
 When injected separately, neither heat-killed, diseasecausing bacteria nor live, harmless bacteria killed the
mice.
 The two types injected together, however, caused fatal
pneumonia.
 Some factor from the ____ bacteria had “transformed”
the harmless bacteria into disease-causing ones.
 From this experiment, biologists inferred that genetic
information could be transformed from one bacterium
to another.
DNA or Proteins?
 But…. Griffith was unsure whether it was __________________________ that was being transformed.
 Almost 20 years later, (1944), Avery, MacLeod, and McCarty recreated Griffith’s experiment in order to
determine if the transforming material was DNA or proteins.
 They discovered that the nucleic acid _______ stores and transmits the genetic information from one
generation to the next.
 Avery, Macleod and McCarty published strong evidence that DNA was the transforming material, but not
enough to convince everyone.
 Many scientists need several different experiments to convince them of a discovery of this importance.
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DNA is the genetic material
In 1952, Alfred Hershey and Martha Chase performed an experiment using radioactively labeled viruses
(_____________________________) that infect bacteria.
These ____________ (phages) were made of only protein and DNA.
The bacteriophages, or viruses, attach to the outside of bacterium, inject its genetic material into bacterium,
take over its processes, and kill it while releasing new phages
The Hershey- Chase Experiment
To determine if the genetic material was DNA or protein, radioactive substances were used as markers.
Hershey and Chase labeled the virus _____________ with a radioactive isotope (pink neon label) and the
virus _______ with a different isotope (blue neon label).
By following the infection of bacterial cells by the labeled viruses, they demonstrated whether it was DNA or
protein that entered the cells and caused the bacteria to produce new viruses.
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The bacteriophages injected only DNA into the bacteria, not proteins.
From these results, Hershey and Chase concluded that the genetic material of the bacteriophage was ______.
Genes…
Scientists now knew that genes are made of _______.
They also knew:
o genes had to carry information from one generation to the next
o genes had to put that information to work by determining the heritable characteristics of organisms
o genes had to be easily copied, because all of a cell’s genetic information is replicated every time a
cell _____________
Scientists now wanted to know more about the molecule DNA.
The Components and Structure of DNA
DNA is a polymer (long chain) made of repeating subunits called ______________.
Nucleotides have three parts: a simple ________, a phosphate group, and a nitrogenous base.
The simple sugar in DNA, called deoxyribose, gives DNA its name—deoxyribonucleic acid.
The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms.
A nitrogenous _______ (nitrogen containing) is a carbon ring structure that contains one or more atoms of
nitrogen.
In DNA, there are four possible nitrogenous bases: ________ (A), guanine (G), cytosine (C), and thymine (T).
Thus, in DNA there are four possible nucleotides, each containing one of these four bases.
DNA Nucleotides
Adenine and Guanine are in a group known as the ______________ (they are larger).
Cytosine and ______________ are in a group called the pyrimidines (they are smaller).
Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the
deoxyribose sugar of an adjacent nucleotide.
The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases
stick out like the ___________ of a zipper.
The nucleotides can be joined together in any order, meaning that any sequence of bases is possible.
Chargaff’s Rule
In the 1950’s Erwin Chargaff analyzed the amounts of four compounds in DNA (________________).
Chargaff’s Rule: [A] = [T] and [G] = [C]
He found that the amount of adenine is always equal to the amount of thymine, and the amount of guanine is
always equal to the amount of cytosine.
X-ray Evidence
X-ray studies done in the 1950’s by Rosalind ____________ and Maurice Wilkins revealed the
basic spiral (coiled double helix) structure of DNA.
X-ray diffraction (crystallography) - x-rays pass through a crystal of a substance onto
photographic film; molecules of substance scatter the x-rays in characteristic patterns
o shows that the strands in DNA are __________ around each other like the coils of a
spring, a shape known as a ____________
o angle of the X suggests that there are ________ strands in the structure
o nitrogenous bases are near the center of the molecule
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The Double Helix
In 1953, Watson and Crick proposed that DNA is made of two chains of nucleotides (wound around each
other) held together by nitrogenous bases (they used the Franklin’s x-ray pattern).
Because DNA is composed of two strands twisted together, its shape is called _____________________.
They discovered that _______________ bonds could form between
certain nitrogenous bases and hold the two strands together.
Because of the size of each of the bases, only adenine and
thymine and guanine and cytosine could form bonds between
them.
This also, supported and explained _______________ rule.
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The Importance of Nucleotide Sequences
The sequence of nucleotides forms the ___________ genetic
information of an organism.
The closer the relationship is between two organisms, the ________
similar their DNA nucleotide sequences will be.
Scientists use nucleotide sequences to determine evolutionary
relationships among organisms, to determine whether ______ people
are related, and to identify bodies of crime victims.
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Prokaryotic Chromosome Structure
Most prokaryotes, such as this E. coli bacterium, have only a ______
circular chromosome.
This chromosome holds most of the organism’s DNA.
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Prokaryote vs. Eukaryote DNA
Eukaryotes have as much as _________ times the amount of DNA as prokaryotes.
Unlike prokaryotes that lack a nucleus, eukaryotic DNA is found in the ____________.
Eukaryotic DNA is organized into chromosomes.
The number of chromosomes can vary by organism.
E. coli Bacterium
Humans have ___ chromosomes
Fruit flies have 8 chromosomes
Giant Sequoia Trees have 22 chromosomes
DNA Length
Chromosome
E. coli (bacteria in human colon) contains 4,639,221 base pairs
Length = 1.6 mm; A typical bacterium is less than 1.6 μm in diameter
DNA must be ____________ into a space only one one-thousandth of its length
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Chromosome Structure of Eukaryotes
A chromosome is made up of a tangled mass of ____________ fiber.
Each chromatin fiber is a __________ wound super coil.
Each super coil is made up of coils.
A coil, in turn, is a chain, of beadlike structures called ________________.
Each nucleosome consists of _________ wound around proteins called histones.
The strand of DNA is a double ___________ made up of nucleotides.
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1. Chromosome
4. Nucleosome
6. DNA
double helix
3. Coils
2. Supercoils
5. Histones
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DNA Replication
Background
 During most of the cell cycle, DNA is unwound, so that the chromosomes are ______ visible.
 During mitosis, the tightly packed chromosomes form in order to move more efficiently.
 Before cell division, DNA must make a copy of itself during S phase of __________________.
 This process is called DNA Replication.
 This process ensures that each resulting cell will have a ________________ set of DNA molecules.
 It is important that the new copies are exactly like the original molecules.
Prokaryote vs. Eukaryote Replication
 During DNA replication, the DNA molecule separates into ________ strands.
 In most prokaryotes, replication begins at a single point in the chromosome and proceeds, often in two
directions, until the entire chromosome is replicated.
 In the larger eukaryotic chromosomes, DNA replication occurs at _____________ of places at the same time.
 Replication proceeds in both directions until each chromosome is completely copied.
 The sites where separation and replication occur are called replication _______________.
New strand
Original
strand
DNA Replication
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Nitrogenous
bases
Original
strand
Steps of DNA Replication
1. DNA Replication begins when the _______ strands separate as the hydrogen bonds that hold the base pairs
together breaks.
2. This allows to the two strands to _________ and unwind.
 Because each original strand can be used to make a new strand, the strands are said to be
complementary.
3. Each strand of the double helix of DNA serves as a ____________, or model, for the new strand.
4. The enzyme ________ polymerase helps free-floating nucleotides match up with their complementary bases
on each of the exposed, original strand.
 Adenine pairs always with thymine and cytosine always pairs with __________, following the rules of
base pairing.
 The addition of nucleotides occurs in ________ directions of the DNA molecules simultaneously.
5. Two new complementary strands are produced.
 Each molecule contains one original strand and one new strand.
 This is why DNA Replication is called _________-conservative
Practice:
Original Strand:
ATCGGCTAA
Complementary Strand: _________________
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