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Chapter12
DNA Study Relationships
13.1 Ecologists
12.1 Identifying the Substance of Genes
Key Questions:
-What clues did bacterial transformation yield
about the gene?
-What role did bacterial viruses play in
identifying genetic material?
-What is the role of DNA in heredity?
Vocabulary:
Transformation
bacteriophage
Warm-up
13.1 Ecologists Study Relationships
What is DNA?
A large molecule found in the nucleus of cells
that is responsible for heredity (passing of
genes from parent to offspring).
Gene: Sequence of DNA
that codes for a protein
and thus determines a
trait; factor that is passed
from parent to offspring
How do we know the function of DNA?
DNA was identified as the genetic material
responsible for heredity through a series of
experiments.
The
discovery of DNA
DNA as the Genetic Material
8.1 Identifying
Rosalind Franklin 1952
Watson and Crick 1953
Franklin
• Rosalind Franklin determined what
elements made up DNA (N & P)
• Watson and Crick used Franklin’s
data to describe the shape of DNA
as a double helix
Watson
Crick
Double Helix
12.1
IdentifyingDNA
the Substance
of Genes
8.1
Identifying
as the Genetic
Material
• What clues did bacterial transformation yield about the
gene?
DNA Structure was not determined until 1950
•-Scientists had to first understand the function of DNA
•It took many scientists observing and experimenting to
determine DNA’s structure
How
do we knowDNA
the function
DNA? Material
8.1 Identifying
as the of
Genetic
KEY CONCEPT
DNA was identified as the genetic material through a
series of experiments.
11
8.1
DNA as
the Geneticyield
Material
WhatIdentifying
clues did bacterial
transformation
about the gene?
Griffith (1924-41): finds “transforming material” (genetic
material)
• Griffith experimented with the bacteria that cause pneumonia.
• He used two forms: the S form (deadly/smooth colonies) and the R
form (not deadly/rough edged colonies).
Concluded: A “transforming material” passed from dead S
bacteria to live R bacteria, making them deadly and this
transforming factor had to be a gene.
Why?
But why did
they die?
11
8.1
DNA as
the Geneticyield
Material
WhatIdentifying
clues did bacterial
transformation
about the gene?
Griffith didn’t know what made up genes so…
• Avery wanted to determine: What was the molecular
cause for transformation?
• Avery isolated and purified Griffith’s transforming factor.
• Avery compared the chemical make-up of four samples
of Griffith’s transforming material to the chemical
make-up of DNA.
11
8.1
DNA as
the Geneticyield
Material
WhatIdentifying
clues did bacterial
transformation
about the gene?
Avery’s Data
Avery’s Conclusion:
– Chemical tests showed the chemical make-up of the
unknown transforming samples matched that of
DNA.
What
role did bacterial
viruses
in identifying
8.1 Identifying
DNA as
the play
Genetic
Material
genetic material?
Hershey and Chase
• Used Viruses that infect bacteria called…
Bacteriophages
– A bacteriophage is a kind of virus that infects bacteria
Hershey
and Chase
DNA is the
11
8.1 Identifying
DNA(1952)
as the“confirm
Genetic that
Material
genetic material”
• Hershey and Chase studied viruses that infect bacteria
(bacteriophages)
• They tagged the DNA
in the virus with radioactive
phosphorus.
• They tagged the proteins
in the virus with radioactive
Bacterial cell
sulfur.
• Exposed tagged viruses to
• Results - Tagged DNA
bacterial cells
was found inside the
bacteria; tagged proteins
were not!
Therefore the function of DNA was determined as the
genetic material responsible for heredity!
8.1
Genetic Material
WhatIdentifying
is the role ofDNA
DNAasinthe
heredity?
The DNA that makes up genes must be cable of…
• Storing Information: information for characteristics &
patterns of development
• Copying Information: a cell copies its DNA before it
divides
• Transmitting Information: genes are passed from one
generation to the next