The Discovery of DNA

1
The Discovery of DNA

• Chance Greengrass
• Bio 446 Lab Methods in Molecular Biology
• Dr. Adema

2
DNA History

• DNA is made of nucleic acids
• Friedrich Miescher (1844-1895)
• The 1st researcher to isolate and identify
  nucleic acid
• Used neutrophils from pus
• Used a procedure that caused precipitation
• Called it nuclein
• Could not figure out its function
• This discovery played an important role in the
  identification of nucleic acids and their role in
  inheritance

3
DNA History

• Chemical composition of nucleic acids
• Albrecht Kossel (1853-1927)
• Described nucleotides A, T, C, G, and U
• Worked under Felix Hoppe-Seyler
• Both expanded upon the work of Miescher
• Found the substance contained phosphorus, but was
  high in acidity
• Unlike any cellular substance that had been
  discovered at that time
• Contained protein and non-protein components
• Non-protein was nucleic acid

4
DNA Theory

• How do inherited traits get passed?
• Nikolai Koltsov (1872-1940)
• Proposed one of the first theories about how
  genetic inheritance works
• giant hereditary molecule...
• ...two mirror strands that would replicate in a
  semiconservative fashion using each strand as a
  template.
• Years prior to Watson and Cricks work
• Work was hindered due to Soviet NKVD

5
Nucleic Acids Carriers of Genetic Info

• Avery-Macleod-McCarty experiment
• Used S. pneumoniae
• S R strains
• S smooth (leathal)
• R rough ( non-leathal)
• Heat killed S
• Non-leathal
• Heat killed S R
• Leathal
• What caused the lethality to be passed from S to
  R?

6
Avery-Macleod-McCarty Experiment
7
Expanding on DNA Knowledge

• Nucleic acids coming together
• Erin Chargaff (1905-2002)
• Developed two rules of DNA
• His work greatly influenced Watson and Crick
• Disproved the tetranucleotide hypothesis
• Helped show that DNA was the genetic material and
  not protein

8
Chargaffs Rules

• Rule 1
• In DNA the number of guanine (G) equals the
  number of cytosine (C), and the number of adenine
  (A) equals the number of thymine (T)
• i.e. in humans A30.9 T29.4 G19.9 and
  C19.8
• Rule 2
• The composition of DNA varies from one species to
  another in the amounts of A, G, T, and C
• This helped to show that DNA, and not protein,
  was better suited to be genetic material

9
Genetic Theories

• Triple Stranded DNA
• 3 oligonucleotides form a triple helix
• Used Hoogsteen or reversed Hoogsteen H-bonds
• Linus Pauling
• Theorized that the phosphates were on the inside
  and that the nucleotides were on the outside
• RNA was one of the original theories
• Not as stable as DNA so DNA was able to maintain
  a longer length
• DNA could handle repair better since it does not
  have uracil
• In RNA sometimes a C can become a U leads to
  errors
• No U in DNA
• DNA is more secure based off of its structure

10
DNA Comparison

• Triple-Stranded

• Double Helix

11
DNA Structure

• Rosalind Franklin (1920-1958)
• An X-ray crystallographer
• Work led to the discovery of DNA double helix
• Not give credit for
• Photo 51
• X-ray diffraction image of DNA
• Showed structure of DNA
• Disproved many other theories
• IMMENSELY influenced Watson and Cricks work

12
Photo 51
13
DNAs True Structure

• Watson Crick
• Published, Molecular Structure of Nucleic Acids
  A Structure for Deoxyribose Nucleic Acid in 1953
• First article to ever describe the double helix
  structure of DNA
• Used the work of Miescher, Kossel, Koltsov,
  Chargaff, and Franklin
• Franklins work was the final piece
• Won Nobel Prize for Medicine in 1962

14
Double Helix

• Double Helical structure for DNA
• Allows safe storage
• Is a strong molecule to store and protect the
  genetic codes within
• Is easy to access and copy
• We use these properties of DNA to study and
  manipulate molecular biology
• Has allowed many advancements in multiple fields
• How we are able to do our work in lab

15
References

• https//en.wikipedia.org/wiki/Molecular_Structure_
  of_Nucleic_Acids_A_Structure_for_Deoxyribose_Nucl
  eic_Acid
• https//www.quora.com/Why-was-DNA-chosen-to-be-the
  -genetic-material-instead-of-RNA
• https//en.wikipedia.org/wiki/Linus_Pauling
• https//en.wikipedia.org/wiki/Nikolai_Koltsov
• https//en.wikipedia.org/wiki/Albrecht_Kossel
• https//en.wikipedia.org/wiki/Friedrich_Miescher
• https//en.wikipedia.org/wiki/Triple-stranded_DNA
• https//en.wikipedia.org/wiki/Chargaff27s_rules
• https//en.wikipedia.org/wiki/Erwin_Chargaff
• https//en.wikipedia.org/wiki/Photo_51
• https//en.wikipedia.org/wiki/Rosalind_Franklin
• http//www.nature.com/nature/journal/v171/n4356/ab
  s/171737a0.html
• Watson, J. D., and F. Crick H. C. "Molecular
  Structure of Nucleic Acids A Structure for
  Deoxyribose Nucleic Acid." Nature 171.4356
  (1953) 737-38. Web.
• http//www.yourgenome.org/stories/revealing-dna-as
  -the-molecule-of-life
• https//en.wikipedia.org/wiki/AveryMacLeodMcCart
  y_experiment