Understanding the Genetic Basis of Inheritance

Early 20th Century Scientific Context

• Physicists and chemists were making significant discoveries about atomic structures.
• The mystery of biological inheritance remained unsolved.
• Scientists were searching for a biological molecule that could explain trait inheritance and evolution.

The Quest for the Genetic Molecule

• In 1951, James Watson and Francis Crick embarked on solving the structure of DNA.
• They met at the Cavendish Laboratory, Cambridge, with complementary backgrounds and a shared passion for science.

Key Scientists

• James Watson: A young American biologist determined to solve DNA's structure.
• Francis Crick: An English physicist who transitioned to biology post-WWII to make up for lost time.
• Morris Wilkins and Rosalind Franklin: Researchers at King's College working on DNA through X-ray crystallography.
• Linus Pauling: A renowned chemist in California, seen as a competitor in the race to solve DNA.

DNA Structure Investigation

Historical Background

• Gregor Mendel's pea plant experiments in the 1860s laid foundations for understanding genetic inheritance.
• By the 1920s, genes were linked to chromosomes composed of proteins and DNA.

The DNA vs. Protein Debate

• Initially, proteins were considered the likely genetic material due to their diversity and functions.
• Oswald Avery's experiments suggested that DNA carried genetic information, influencing Watson and Crick’s focus on DNA.

X-ray Crystallography

• Technique crucial for determining molecular structures, albeit challenging due to equipment limitations.
• King's College, London, led by Wilkins and Franklin, was using this method on DNA.

Key Discoveries and Developments

Watson and Crick's Approach

• Inspired by Franklin's X-ray diffraction data, Watson and Crick attempted to model DNA.
• Their first model was incorrect due to misremembered data but was part of their learning process.

The Role of Competition

• Watson, Crick, and others were motivated by the looming competition from Linus Pauling.
• Franklin's photo 51 and Crick's insights into DNA's symmetry were pivotal.

Final Discovery: The Double Helix

• The model revealed the structure as a double helix with sugar-phosphate backbones and paired bases inward.
• Complementary base pairing explained gene replication and mutation:
  • Adenine (A) pairs with Thymine (T).
  • Guanine (G) pairs with Cytosine (C).

Impact and Legacy

• The structure of DNA was published in 'Nature' and quickly recognized for its profound implications.
• The discovery explained both the stability and evolutionary adaptability of life.
• Watson, Crick, and Wilkins received the Nobel Prize nine years later.
• The model opened new pathways for biological research, decoding the mysteries of life.