Download DNA History Notes

BELL RINGER 9-17-15
1.
How is diffusion different from an ion pump?
a.
b.
c.
d.
2.
Most animal cell membranes have proteins that pump ________
ions out of the cell and potassium ions into the cell.
a.
b.
c.
d.
3.
Diffusion takes place due to osmotic pressure
Diffusion requires the cell to use energy for the transfer of molecules
Diffusion does not transfer all of the ions across the cell membrane
Diffusion transfers molecules from an area of high to low concentration
Calcium
Carbon
Magnesium
Sodium
Living cells use _______________ as their main source of energy.
a.
b.
c.
d.
Carbohydrates
Cellulose
Lipids
Proteins
AGENDA
Standard
 Notes – A History Lesson
 Timeline
 Closing – Crossword Puzzle

STANDARD

SB2. Students will analyze how biological traits
are passed on to successive generations.
Distinguish between DNA and RNA.
 Explain the role of DNA in storing and transmitting
cellular information

DISCOVERING DNA

3 major experiments that led to the conclusion
that DNA is the genetic material in cells:
Griffith’s Discovery of Transformation
 Avery’s Experiments with Nucleic Acids
 Hershey-Chase Experiment

GRIFFITH’S DISCOVERY OF
TRANSFORMATION
When: 1928
 Who: Frederick Griffith
 What:

He was working with two related strains of bacteria
 One strain, S, causes pneumonia and is covered by a
capsule made of polysaccharides.
 The other strain, R, has no capsule and doesn’t cause
pneumonia.
 What caused the pneumonia? The bacteria or the
capsule?

HOW
Griffith used mice to
test the bacteria.
 S bacteria caused
pneumonia.
 And, R bacteria is
completely harmless.

HOW




He decided to use heat to kill the bacteria (the capsule
remained).
When the mice were injected with the heat killed S strain
they did not get sick and die.
When they were injected with heat killed S strain and live R
strain they got sick and died, and live S strain was withdrawn
from the dead mice
Conclusion: transformation – a change in the genotype that is
caused when cells take up foreign material.

Huh? The R strain that was not lethal took up foreign material from
the S strain and transformed into the lethal S strain
WHAT CAN WE LEARN FROM GRIFFITH’S
EXPERIMENTS?
Genetic material can be transferred between
cells.
 Still, no one knew that this genetic material was
DNA. (That’ll come later.)

AVERY’S EXPERIMENTS WITH NUCLEIC
ACIDS
When: 1940s
 Who: Oswald Avery
 What:


He wanted to figure
out if the transforming
agent in Griffith’s
experiment was
protein, RNA, or,
DNA.
HOW



In trying to determine if
the transforming agent
was DNA, RNA, or
protein Avery used
enzymes to destroy each
of these molecules in
heat-killed S bacteria.
S bacteria that were
missing protein and
RNA were able to
transform R cells into S
cells.
S bacteria without DNA
did not transform R
cells.
WHAT CAN WE LEARN FROM AVERY’S
EXPERIMENTS?
DNA is responsible for transformation in
bacteria.
 No idea what it looks like though!

HERSHEY-CHASE EXPERIMENT
When: 1952
 Who: Alfred Hershey and Martha Chase
 What:


Wanted to determine how DNA affected other cells.
HOW
Studied bacteriophages (viruses that infect
bacterial cells and cause the cells to produce
viruses)
 They knew that protein has sulfur but not
phosphorous and DNA has phosphorous but not
sulfur.
 http://highered.mcgrawhill.com/olc/dl/120076/bio21.swf

WHAT CAN WE LEARN FROM THE
HERSHEY-CHASE EXPERIMENT?

DNA is the hereditary material.
DISCOVERING DNA’S STRUCTURE
How did Watson and Crick figure out that DNA
has a double helical structure?
 They used information from experiments by
Chargraff, Wilkins, and Franklin.

CHARGRAFF’S OBSERVATIONS
When: 1950
 Who: Erwin Chargraff
 What:


For each organism he studied:
Amount of A=T
 Amount of G=C

FRANKLIN AND WILKINS – PHOTOGRAPHS
OF DNA
When: 1952
 Who: Rosalind Franklin and Maurice Wilkins
 What:

Developed high-quality x-ray diffraction
images of DNA
 The images suggested that a DNA molecule
resembled a tightly coiled helix made of two
chains of nucleotides.

WATSON & CRICK
When: 1953
 Who: James Watson and Francis Crick
 What:

Set out to physically build a 3D model of
DNA
 Took into account Chargraff’s data and
Franklin’s x-ray diffraction studies
 Also used their knowledge of chemical
bonding

HOW
Used paper models of the bases to figure out the
base pairs of pyrimidines with purines.
 Made a 3D model of a DNA double helix using
tin, wire, and other materials.

TIMELINE
Use the pictures, dates, and names provided to
create an accurate timeline.
 Be sure to include a summary of the experiments
and conclusions

Griffith
Avery
Chargraff
Franklin