π¬
The Lac Operon System
Historical Context: 1950s-60s pre-digital era research
Classical Wet Chemistry Techniques
π§« Bacterial
Cultures
βοΈ Growth
Media
π¬ Enzyme
Assays
π Chemical
Analysis
β’ Genes organized in clusters called "operons"
β’ Bacteria respond intelligently to nutrients
β’ Foundation of gene regulation
ποΈ
Gene Regulation Mechanism
Revolutionary Find: Repressor proteins act as molecular switches
The Molecular Switch
π BLOCKED
Repressor ON
β‘
β’ Discovered negative gene control
β’ Repressor binds to DNA, blocks production
β’ Lactose inactivates repressor
π‘
Messenger RNA Discovery
Central Dogma: Proved mRNA carries genetic information
Information Flow in All Living Cells
β’ mRNA = molecular messenger
β’ Bridges DNA and protein synthesis
β’ Universal biological principle
π
Negative Gene Regulation
Paradigm Shift: Genes can be actively "turned off"
β’ Cells actively control gene expression
β’ Responsive to environmental conditions
β’ Revolutionary biological concept
1
Bacterial Cultures
Grew E. coli in different sugar solutions, measured growth rates
2
Enzyme Assays
Chemical tests to measure Ξ²-galactosidase production over time
3
Induction Experiments
Added/removed lactose, tracked cellular responses chemically
4
Genetic Complementation
Mixed bacterial strains, analyzed resulting enzyme patterns
5
Quantitative Analysis
Mathematical models of growth phases and reaction kinetics
6
Protein Purification
Isolated repressor proteins (only ~10 molecules per cell!)
βοΈ "Wet Chemistry" Innovation
Pre-Digital Era Genius: All discoveries made using traditional lab techniques - no DNA sequencing, PCR, or computers!
π§« Continuous Cultures
Invented "bactogène" device for steady-state bacterial growth
π Chemical Kinetics
Applied reaction rate analysis to biological systems
π¬ PaJaMa Experiment
Famous 1957 bacterial mating study using simple techniques