Today:
Notes Quiz 12-1
Lecture on History
Race to the Double Helix
DNA
DNA
HISTORY
HISTORY!
Homework up till Winter Break!
Wednesday: Read/notes Chapter 12 Section 1
Thursday: Twist of Fate Article w/ Questions p. 49-52
Friday/Weekend: Twist of Fate Article w/ Questions p.
53-56
Monday: Twist of Fate Article w/ Questions p. 57-58
Tuesday: DNA Coloring
Next Friday: DNA History Test!
How did scientists determine
which molecule carries genetic
information from parent to
offspring and gives us our traits?
PROTEIN VS DNA
Griffith’s Contribution
1928: Griffith discovered that one bacteria
can transfer it’s genetic information to
another bacteria. Transformation!
How did he do it…by killing a lot of mice
But…we still didn’t know what molecule
controlled the genetic information.
FYI: You will do this in lab second semester…transformation, not mouse
killing.
What
does
bacteria
really
look like
when it
is grown
in a lab?
When he killed
the “bad”
bacteria, a few
survived and
passed those
“survivor” traits
to the “good”
bacteria along
with the rest of
it’s genetic
information.
Avery’s Contribution
1944: Avery repeated Griffith’s experiment
but he destroyed all proteins first.
Transformation still occurred proving that the
“transforming” material was DNA.
How did he do it…by killing more mice
Hershey & Chase’s
Contribution
1952: Tagged a bacteriophage (virus that
invades bacteria) with radioactive markers
on the protein molecules and the DNA.
Observed that when the virus injects it’s
genetic information into the bacteria, that
molecule is actually DNA and not a protein.
How did he do it…not by killing mice
Now that multiple experiments
have proven DNA to be the
genetic molecule, the race was
on to discover DNA’s structure
and function.
Franklin’s Contribution
1952: Franklin uses x-ray diffraction
technology to gain clues to DNA structure.
Helical? Double Helix? Triple Helix?
How did she do it…by personally absorbing
many x-rays
Chargaff’s Contribution
1952: Chargaff studies the % of each
nucleotide in a DNA sequence for multiple
organisms. Discovers that
% adenine = % thymine
% cytosine = % guanine
How did he do it…extracting DNA from a
large variety of organisms.
Watson & Crick’s
Contribution
1952: Built a three dimensional model of
DNA showing the double helical structure.
Published their findings in Nature magazine
sharing with the world the structure of DNA.
How did they do it…by applying the
experimental results from many scientists
and applying this to model building.
Side Note…Maurice
Wilkins
Franklin worked with Maurice Wilkins who
was also a leading x-ray diffraction scientist.
Wilkins helped Watson & Crick interpret
Franklin’s images so they could build their
double helical model.
Scientist
Picture
Location
Year
Contribution
Griffith
England
1923
Genetic information can be
transferred from one bacteria to
another
Avery
New York,
US
1944
DNA is the genetic material
transferred in Griffith’s experiment.
HersheyChase
New York,
US
1952
Used bacteriophage to prove DNA
is the molecule containing genetic
information.
Chargaff
New York,
US
1950
%A = %T; %G = %C
Franklin
England
1952
X-Ray images suggest double
helix.
WatsonCrick
England
1952
Built model proving DNA’s double
helical structure.
Wilkins
England
1952
Helped Watson and Crick interpret
Franklin’s images.