Starter for 10 ....
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Starter for 10 .... • What type of experiment would you design to determine that DNA is the source of all genetic information? Hint ..... • What do you know about how DNA was discovered?
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Starter for 10. What type of experiment would you design to determine that DNA is the source of all genetic information? Hint ..... What do you know about how DNA was discovered?. Higher Human Biology Unit 1 – Human Cells DNA. Learning Outcomes. Content - PowerPoint PPT Presentation
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Starter for 10 ....
• What type of experiment would you design to determine that DNA is the source of all genetic information?
Hint .....• What do you know about how DNA was
discovered?
Higher Human Biology Unit 1 – Human Cells
DNA
Learning OutcomesContent• Identify the key scientists and the journey of
discovering DNA
Process• Computer research
Benefit• Process of how science works!
GregorMendel
Wilkins&
Franklin
FrederickGriffith
AntonieVan
Leeuwenhoek
OsmondAvery
Watson &
Crick
The DNA puzzle .....
Hershey &
Chase
Chargaff
???
1. Long Search:
The search for the secret of life dates back nearly a century prior to Watson and Crick’s ground breaking discovery in 1953
1865
1909 1911 195019441929
Gregor Mendel: Introduces the concept of heredity
1865 1909 1911 1929 1944 1950
The Early Efforts
Wilhelm Johannsen: Coins the term “Gene”
1865
1909 1911 1929 1944 1950
The Early Efforts
Thomas Hunt Morgan: Discovers that genes are responsible for inheritance
1865
1909 1911 1929 1944 1950
The Early Efforts
Phoebus Levene: Discovers that DNA is made up of nucleotides, phosphates, sugars and 4 bases
1865
1909 1911 1929 1944 1950
The Early Efforts
Oswald Avery: Shows that DNA can transform the property of cells
1865
1909 1911 1929 1944 1950
The Early Efforts
However, this idea was not universally accepted
Erwin Chargaff: Shows that: A + G = T + C = 50%
1865
1909 1911 1929 1944 1950
The Early Efforts
Chargaff’s Rule is an important equation in the discovery of the structure of DNA
Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation• Frederick Griffiths was a
bacteriologist studying pneumonia
• He discovered two types of bacteria:– Smooth colonies– Rough colonies
CONCLUSION:
The smooth colonies must carry
the disease!
Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation
• When heat was applied to the deadly smooth type…
• And injected into a mouse…
• The mouse lived!
• Griffith injected the heat-killed type and the non-deadly rough type of bacteria.
• The bacteria “transformed” itself from the heated non-deadly type to the deadly type.
Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation
Griffith’s Experiment did not prove that DNA was responsible for transformation
How would you design an experiment to prove that DNA
was responsible for transformation?
Avery, McCarty, and MacLeodRepeated Griffith’s Experiment
Oswald AveryOswald Avery Maclyn McCartyMaclyn McCarty Colin MacLeodColin MacLeod
Avery, McCarty, and MacLeodAdded the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth
Type
CarbohydratesCarbohydrates LipidLipidss
ProteinProteinss
RNARNA DNADNA
To the Heat-Killed Smooth Type, To the Heat-Killed Smooth Type, added enzymes that added enzymes that
destroyed…destroyed…
S-Type S-Type Carbohydrates Carbohydrates
DestroyedDestroyed
S-Type S-Type Lipids Lipids
DestroyeDestroyedd
S-Type S-Type Proteins Proteins DestroyeDestroye
dd
S-Type S-Type RNA RNA
DestroyeDestroyedd
S-Type S-Type DNA DNA
DestroyeDestroyedd
Conclusion:Conclusion:
DNA was the DNA was the transforming factor!transforming factor!
The Hershey-Chase Experiment
Alfred Hershey & Martha Chase worked with a
bacteriophage:
A virus that invades bacteria.
It consists of a DNA core and a
protein coat DNADNA
Protein coatProtein coat
Protein coats of bacteriophages labeled with Protein coats of bacteriophages labeled with Sulfur-35Sulfur-35
DNA of bacteriophages labeled with Phosphorus-32DNA of bacteriophages labeled with Phosphorus-32
BacteriumBacterium
BacteriumBacterium
PhagePhage
PhagePhage1.1. Hershey and Chase Hershey and Chase
mixed the mixed the radioactively-radioactively-labeled viruses labeled viruses with the bacteriawith the bacteria
The viruses infect The viruses infect the bacterial cells.the bacterial cells.
Protein coats of bacteriophages labeled with Protein coats of bacteriophages labeled with Sulfur-35Sulfur-35
DNA of bacteriophages labeled with Phosphorus-DNA of bacteriophages labeled with Phosphorus-3232
2.2. Separated the Separated the viruses from the viruses from the bacteria by bacteria by agitating the virus-agitating the virus-bacteria mixture in bacteria mixture in a blendera blender
Protein coats of bacteriophages labeled with Protein coats of bacteriophages labeled with Sulfur-35Sulfur-35
DNA of bacteriophages labeled with Phosphorus-DNA of bacteriophages labeled with Phosphorus-3232
3.3. Centrifuged the mixture so Centrifuged the mixture so that the bacteria would form a that the bacteria would form a pellet at the bottom of the test pellet at the bottom of the test tubetube
4.4. Measured the radioactivity in Measured the radioactivity in the pellet and in the liquidthe pellet and in the liquid
The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion:
DNA carries the genetic code!
However, there were still important details to
uncover…
The Race to Discover DNA’s Structure
The Race to Discover DNA’s Structure
Linus Linus PaulingPauling 1940s1940s
Discovered the Discovered the alpha-helical alpha-helical structure of proteins.structure of proteins.
The Race to Discover DNA’s Structure
19501950
Chargaff’s Rule: Chargaff’s Rule: Equal amounts of Equal amounts of AAdenine and denine and TThymine, and equal hymine, and equal amounts of amounts of GGuanine uanine and and CCytosineytosine
Erwin Erwin ChargaffChargaff
Why do you think Why do you think the bases match up the bases match up
this way?this way?
Purine + Purine = Too widePurine + Purine = Too wide
Pyrimidine + Pyrimidine = Too Pyrimidine + Pyrimidine = Too NarrowNarrow
Purine + Pyrimidine = Perfect Fit from X-ray Purine + Pyrimidine = Perfect Fit from X-ray datadata
The Race to Discover DNA’s Structure
Maurice Maurice WilkinsWilkins
Rosalind Rosalind FranklinFranklin
X-Ray diffraction image of X-Ray diffraction image of DNA taken by Franklin in DNA taken by Franklin in
19511951
The Race to Discover DNA’s Structure
James WatsonJames Watson Francis CrickFrancis Crick
19531953
Compiled data Compiled data from previous from previous scientists to scientists to build a double-build a double-helical model of helical model of DNADNA
The Race to Discover DNA’s Structure was Over
• DNA is made up of:– Four nucleotides: Adenine, Thymine,
Guanine and Cytosine– These follow the rules of base-pairing:
• Adenine bonds with Thymine• Guanine bonds with Cytosine
– A sugar-phosphate backbone
• DNA is arranged in an double-helix
• Research a scientist and their breakthrough experiment
• Ready to present!
• 2 stars and a wish!
