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Bio10-C12.1 DNA The Genetic Material

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DNA: The Genetic Material
Teacher: Maher Zeidan
Section 1: DNA: The Genetic Material
The discovery that
DNA is the genetic
code involved many
experiments.
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?
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DNA: The Genetic Material
Vocabulary
Review
•
nucleic acid
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New
•
•
double helix
nucleosome
DNA: The Genetic Material
Discovery of the Genetic Material
• After the rediscovery of Mendel’s work,
scientist began to look for the molecule
involved in inheritance.
• 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
•
First major experiment searching for the genetic material
•
Involved transformation between two forms of S. pneumoniae
•
Set the stage for the search to identify the transforming substance
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DNA: The Genetic Material
Griffith's experiment
Discovery of the Genetic Material
Avery
•
Identified the molecule that transformed the R strain of S. pneumoniae into the
S strain
•
Concluded that when the S cells were killed, DNA was released
•
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
•
Used radioactive labeling to trace bacteriophage
DNA and protein.
•
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
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DNA: The Genetic Material
DNA Structure
Nucleotides
•
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
•
Analyzed the amount of A, G, T,
and C in the DNA of various
species
•
Chargaff’s rule: C = G and T = A
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DNA: The Genetic Material
DNA Structure
The structure question
•
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
•
X-ray diffraction techniques indicated that DNA was a double helix, or
twisted ladder shape.
•
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
•
Using Franklin and Chargaff’s data, Watson and Crick measured the
width of the helix and the spacing of the bases.
•
They built a model that conformed the Franklin and Chargaff’s data.
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DNA: The Genetic Material
DNA Structure
DNA structure
•
DNA often is compared to a
twisted ladder.
• Rails of the ladder are
represented by the
alternating deoxyribose and
phosphate.
• The pairs of bases (cytosineguanine or thymine-adenine)
form the steps.
•
Purine base always binds to a
pyrimidine base
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DNA: The Genetic Material
DNA Structure
Orientation
•
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
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DNA: The Genetic Material
Chromosome Structure
•
In prokaryotes, DNA molecules are contained in the cytoplasm, and consist
mainly of a ring of DNA and associated proteins.
•
In eukaryotes, DNA is organized into individual chromosomes.
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DNA: The Genetic Material
DNA in Prokaryotes & Eukaryotes
Chromosome Structure
•
To fit into a cell, DNA coils around a group of beadlike proteins called
histones.
•
DNA + histones form a nucleosome, which group together into chromatin
fibers, which supercoil to form a chromosome.
Copyright © McGraw-Hill Education
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
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