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Section 1: DNA: The Genetic Material
The discovery that DNA is the genetic code involved many
experiments.
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What I Know
W
What I Want to Find Out
L
What I Learned
Essential Questions
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Which experiments led to the discovery of DNA as the genetic material?
What is the basic structure of DNA?
What is the basic structure of eukaryotic chromosomes?
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DNA: The Genetic Material
Vocabulary
Review
New
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nucleic acid
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double helix
nucleosome
DNA: The Genetic Material
Discovery of the Genetic Material
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After the rediscovery of Mendel’s work, scientist began to look for the
molecule involved in inheritance.
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For many years, scientists struggled to determine if DNA or protein was the
source of genetic information.
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DNA: The Genetic Material
Discovery of the Genetic Material
Griffith
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First major experiment searching for the genetic material
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Involved transformation between two forms of S. pneumoniae
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Set the stage for the search to identify the transforming substance
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DNA: The Genetic Material
Discovery of the Genetic Material
Avery
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Identified the molecule that transformed the R strain of S. pneumoniae into
the S strain
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Concluded that when the S cells were killed, DNA was released
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R bacteria incorporated this DNA into their cells and changed into S cells
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DNA: The Genetic Material
Discovery of the Genetic Material
Hershey and Chase
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Used radioactive labeling to trace bacteriophage
DNA and protein.
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Concluded that the bacteriophage DNA was
injected into the cell and provided the genetic
information needed to produce new viruses.
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DNA: The Genetic Material
Summary of Hershey-Chase Results
Interactive Table
FPO
Add link to interactive table from page 328 (table 1) here.
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DNA: The Genetic Material
DNA Structure
Nucleotides
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Nucleotides are the subunits of nucleic acids, and consist of
• 5-carbon sugar
• Phosphate group
• Nitrogenous base
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DNA: The Genetic Material
DNA Structure
Chargaff
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Analyzed the amount of A, G, T,
and C in the DNA of various
species
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Chargaff’s rule: C = G and T = A
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DNA: The Genetic Material
DNA Structure
The structure question
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Search for the structure of DNA was lead by four scientists:
• Rosalind Franklin, British chemist
• Maurice Wilkins, British physicist
• Francis Crick, British physicist
• James Watson, American biologist
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DNA: The Genetic Material
DNA Structure
X-ray diffraction
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X-ray diffraction techniques indicated that DNA was a double helix, or
twisted ladder shape.
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The double helix shape was formed by two strands of nucleotides
twisted around each other.
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DNA: The Genetic Material
DNA Structure
Watson and Crick
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Using Franklin and Chargaff’s data, Watson and Crick measured the
width of the helix and the spacing of the bases.
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They built a model that conformed the Franklin and Chargaff’s data.
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DNA: The Genetic Material
DNA Structure
DNA structure
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DNA often is compared to a twisted ladder.
• Rails of the ladder are represented by the alternating deoxyribose
and phosphate.
• The pairs of bases (cytosine-guanine or thymine-adenine) form the
steps.
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Purine base always binds to a pyrimidine base
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DNA: The Genetic Material
DNA Structure
Orientation
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DNA molecules have specific orientations of the two strands
• On the top rail, the strand is said to be oriented 5’ to 3’.
• The strand on the bottom runs in the opposite direction and is
oriented 3’ to 5’.
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DNA: The Genetic Material
Structure of DNA
Animation
FPO
Add link to animation from page 331(Figure 8) here.
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DNA: The Genetic Material
Chromosome Structure
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In prokaryotes, DNA molecules are contained in the cytoplasm, and
consist mainly of a ring of DNA and associated proteins.
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In eukaryotes, DNA is organized into individual chromosomes.
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DNA: The Genetic Material
Chromosome Structure
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To fit into a cell, DNA coils around a group of beadlike proteins called
histones.
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DNA + histones form a nucleosome, which group together into
chromatin fibers, which supercoil to form a chromosome.
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DNA: The Genetic Material
Review
Essential Questions
•
•
•
Which experiments led to the discovery of DNA as the genetic material?
What is the basic structure of DNA?
What is the basic structure of eukaryotic chromosomes?
Vocabulary
•
•
double helix
nucleosome
Copyright © McGraw-Hill Education
DNA: The Genetic Material