Molecular Biology Lecture

Introduction

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Making the Link: Function and Gene

• Connection Steps
  • Mutants and Biochemistry: Connecting function to gene using mutants.
  • Biochemistry of Genetics:
    • Biochemistry involves purifying things in a test tube.
    • Genetics involves heredity.
  • Objective: Purify heredity in a test tube.

Purifying Heredity: The Transforming Principle

• Defining the Transforming Principle:
  • Transforming principle as a substance responsible for transferring heredity.
  • Key work in 1928 by F. Griffiths on pneumococcus.

Griffiths' Experiment

• Purpose: Griffiths aimed to create a vaccine for pneumococcus after the 1918 Spanish influenza epidemic.
• Bacteria Types:
  • Smooth, Virulent Bacteria: Smooth glistening coat, virulent, mouse dies.
  • Rough, Non-virulent Bacteria: Rough coat, non-virulent, mouse lives.
• Key Experiment:
  • Injects smooth virulent: Mouse dies.
  • Injects rough non-virulent: Mouse lives.
  • Heat-killed smooth virulent: Mouse lives.
  • Combined live rough and dead smooth: Mouse dies; live smooth virulent bacteria found in blood.
• Implication: Dead bacteria transformed live non-virulent bacteria into virulent.

Avery, McCarty, and MacLeod's Work

• Continuation of Griffiths' Work
  • Avoided using mice; used bacterial plating techniques.
  • Discovered that the transforming substance was DNA.

Hershey and Chase Experiment (1952)

• Study: Viruses infecting bacteria (bacteriophages).
• Components of Virus: Protein coat, DNA inside.
• Experiment Method:
  • Tagged protein with Sulfur-35, DNA with Phosphorus-32.
  • Blender experiment to separate virus from bacteria.
  • Found P-32 inside bacteria; confirmed DNA as genetic material.

Structure of DNA: Discovery by Watson and Crick

• Background: Influenced by Rosalind Franklin's x-ray diffraction.
• Model Proposal (1953): Double helix structure.
  • Strands run anti-parallel (5' to 3')
  • Base pairing: Purines (A, G) pair with Pyrimidines (T, C).
  • Hydrogen bonds: A-T (2 bonds), C-G (3 bonds).
• Significance: DNA replication, heredity, and mutation.

Confirmation of Semi-Conservative Replication: Meselson-Stahl Experiment (1957-1958)

• Method: Grew E. coli in Nitrogen-15 medium, then switched to Nitrogen-14.
• Discovery: DNA replication resulted in hybrid DNA with intermediate density.

Conclusion

• Bridging Genetics and Biochemistry: Establishes the foundation for molecular biology.
• Next Class: Further exploration of molecular biology connections.