DISCOVERY OF DNA
Chapter 12.1
Discovery of Genetic Material
• Scientists knew genetic information
was carried on the chromosomes
• They did not know where on the
chromosomes it was
• Two main parts of chromosomes are
DNA and proteins
Frederick Griffith- 1928
• First main discovery of DNA as genetic
material
• Working with two strains of
Streptococcus pneumoniae he
discovered that one strain could be
transformed by the other
• Smooth strain (S) and rough strain (R)
Frederick Griffith - 1928
• Experiment 1 - Smooth killed the host
(mouse)
• Experiment 2 -Rough did not kill
the mouse
• Experiment 3 – heated smooth did
not kill mouse
• Experiment 4- Mixture of heated
smooth and rough killed mouse
Frederick Griffith - 1928
Oswald Avery- 1944
• Avery and colleagues identified the
molecule that transformed the R strain
into the S strain - not widely accepted
• Conclusion: In Griffith’s experiment
when S cells were killed, they released
DNA and the R cells incorporated it
into their cells, changing the bacteria
into S cells.
Alfred Hershey and Martha Chase- 1952
• Provided evidence that DNA was the
transforming factor
• Used virus (bacteriophage) made
of DNA and protein
• Viruses have to inject DNA into
living material into a cell to
reproduce
Alfred Hershey and Martha Chase- 1952
• Radioactive labeled the virus
(bacteriophage) to see which part was
injected into the bacteria
• Experiment 1 – radioactive label on
the Protein coat of Virus.
• Experiment 2 – Radioactive label on
the DNA of Virus
Alfred Hershey and Martha Chase- 1952
NO protein
transferred
DNA is
transferred
Copy the Questions to your notes!
1. What conclusion did Frederick Griffith
make about bacteria?
That one strain can be
transformed by another
2.
What conclusion did Hershey and
chase make about DNA?
The genetic material is in the
DNA not the protein
STRUCTURE AND
FUNCTION OF DNA
Chapter 12.1
•Humans share 50% of their DNA with bananas.
•Cells can contain 6-9 feet of DNA. If all the DNA in your body
was put end to end, it would reach to the sun and back over 600
times.
•DNA in all humans is 99.9 percent identical. It is about one
tenth of one percent that makes us all unique, or about 3 million
nucleotides difference.
•In an average meal, you eat approximately 55,000,000 cells or
between 63,000 to 93,000 miles of DNA.
•It would take a person typing 60 words per minute, eight hours
a day, around 50 years to type the human genome.
What is DNA?
• P.A. Levene (1920’s)- Determined DNA is
made up of 2 chains of nucleotides
Nucleotides
• Each nucleotide has 3 parts.
Deoxyribose sugar
2. Phosphate group
3. Nitrogenous base (4 types)
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)
1.
Nucleotides
• Purines – Made
up of two rings
(A,G)
• Pyrimidines –
made up of
only one ring.
(T,C)
Erwin Chargaff- 1950
• Analyzed the amounts of nitrogenous
bases found in DNA
• Conclusion: the amount of adenine
nearly is the same as the amount of
thymine and the same for guanine and
cytosine.
• C=G T=A
Erwin Chargaff- 1950
• Adenine=Thymine
• Cytosine=Guanine
Franklin and Wilkins
• Via the use of
x-ray
diffraction,
Rosalind
Franklin and
Maurice
Wilkins’ took
this photo of
DNA.
Rosalind Franklin’s
Photo 51
Watson and Crick
• DNA is a double helix
structure. (Twisted
ladder)
• 2 complementary paired
strands of nucleotides
twisted around each
other. (rungs)
• Sugar and phosphate
backbone (sides of
ladder)
DNA Structure
• Cytosine (C) and
guanine (G) bases
pair to each other by
3 hydrogen bonds
• Thymine (T) and
adenine (A) base pair
to each other by
2 hydrogen bonds
Functions of DNA
• DNA directs the machinery of a cell to
make specific proteins, and, therefore,
DNA indirectly controls all of the
functioning of all living things.
Functions of DNA
• DNA stores hereditary information of
an individual
Functions of DNA
• DNA has the ability to mutate
(change). This allows for new
characteristics and abilities to appear
which may help an individual to
survive and reproduce (EVOLUTION).
Functions of DNA
• DNA can replicate it’s self (Make
copies)
Chromosomes and DNA
• DNA is organized into chromosomes
• DNA coils around proteins called
histones (form nucleosomes)
• Nucleosome supercoil to make up
DNA structure we know as a
chromosome
If all organisms are made of the same
4 nucleotides in their DNA, how are
they so different?
• Every organism has a different DNA
sequence, which provides different
information
• The more closely related two
organisms are, the more similar their
DNA nucleotide sequences will be.
Copy the questions to your notes!
The nitrogenous base Adenine (A)
T
always bonds with ____
2. The Nitrogenous base Cytosine (C)
G
always bonds with ____
3. Who discovered the structure of
DNA? Watson and Crick
4. DNA coils around proteins called
Histones
_____________
1.