The Discovery of the Structure of DNA

1
Chapter 16

• Lecture 2
• The Discovery of the Structure of DNA

2
Discovery of DNA Structure

• Structure was Published in 1953
• James Watson
• American biologist
• Francis Crick
• British Physicist
• Unsung Hero
• Rosalind Franklin
• Took the x-ray crystallography pictures of the
  DNA
• Without the pictures the structure would never
  have been determined!
• Book that caused a paradigm shift in the way
  biologists thought about life and probably paved
  the way for this discovery
• What is Life? by Erwin Schrödinger
• Controversial Book
• The Double Helix
• Published in the 1960s
• Watsons memoirs regarding the discovery
• Politically incorrect- it upset many people
• I have never seen Francis Crick in a modest
  mood.

3
Chargaffs Rule

• Chargaffs Rule was an important piece of data to
  help determine the structure of DNA
• The amount of adenine equals the amount of
  thymine
• The amount of guanine equals the amount of
  cytosine
• These ratios are true in a wide variety of
  organisms

4
Rosalind Franklins X-ray photos

• By sending x-rays through a crystallized form of
  DNA a diffraction pattern is created.
• From this diffraction pattern a scientist can
  infer the structure of the crystal.
• This is not an easy task (getting the photos is
  hard and interpreting the photos is tricky)
• Rosalind Franklin took the photos, Watson and
  Crick interpreted them

5
Nitrogenous Bases

• Nitrogenous bases
• Pyrimidines
• Thymine
• Cytosine
• Purines
• Adenine
• Guanine
• Pairing
• A-T
• C-G
• Hydrogen bonding holds them together

6
DNA Structure

• Double Helix
• Sugar-Phosphate backbone
• Deoxyribose sugar
• Linked 5 carbon to 3 carbon
• Anti-parallel
• Run in opposite directions