Discovery of DNA Structure

Introduction

• Early 20th century: Physicists and chemists unlocked atomic secrets.
• Mystery of inheritance: Traits passed from generation to generation, but how?

The Challenge

• Need for a biological molecule to store and transmit genetic information.
• Must explain:
  • Stability of life (traits passed faithfully)
  • Mutability of life (change for evolution)

Watson and Crick's Collaboration

• Key Figures:
  • James Watson:
    • 23-year-old American, passionate about science.
    • Unique style (crew cut, gym shoes).
  • Francis Crick:
    • Englishman and physicist, returned to science post-WWII.
    • Eager to make up for lost time, interested in biology.
  • Both shared a love for science and the goal of solving the gene structure.

Historical Context

• Gene theory dates back to Gregor Mendel's work in the 1860s.
• Genes located in cell nuclei, associated with chromosomes (DNA and proteins).
• Debate: Are genes made of DNA or protein?
  • Protein seemed more complex and interesting.
  • DNA perceived as simple (sugar, phosphate, bases).

Avery's Experiment

• Oswald Avery demonstrated DNA carries genetic information, challenging existing views.
• Watson and Crick considered Avery’s work significant.

X-ray Crystallography

• Essential technique for solving molecular structures.
• Challenges:
  • Difficult to interpret diffraction patterns.
  • Primitive equipment in the 1950s.
• Cavendish Laboratory's director opposed working on DNA due to competition with King's College.

Competition and Collaboration

• Key Players:
  • Morris Wilkins:
    • Led DNA research at King's College.
  • Rosalind Franklin:
    • Talented crystallographer, wanted to lead her project.
    • Encountered challenges due to gender biases in science.
• Watson and Crick monitored King's College's progress while working underground.
• Linus Pauling:
  • Renowned chemist proposing a triple helix model, increasing competition.

Breakthroughs in Understanding DNA

• Watson analyzed Franklin's presentation and proposed models.
• Franklin’s Photo 51 revealed a helical structure, crucial for their understanding.
• Crick's insights on DNA symmetry led to crucial discoveries about backbones.

Development of the Double Helix Model

• Watson started building models, experimenting with base pairing.
• Chargaff’s rules: A=T and G=C ratios led to pairing insights.
• February 28, 1953: Model fit measurements and explained replication and mutation.
  • Genetic information stored in base sequences.
  • Mutations occur with sequence changes.

Impact and Recognition

• Discovery explained stability and mutability of life.
• Published in Nature, gaining worldwide recognition.
• Nobel Prize awarded nine years later, marking a significant scientific achievement.

Conclusion

• The double helix discovery opened new avenues for biological research, providing insights into life's mysteries.