BIOL 142 Lecture Notes - Lecture 21: Operon, Cyclic Adenosine Monophosphate, Replica Plating
Biology 142- Lecture 21- Gene Regulation
Gene Regulation
• Our current understanding of gene regulation started out with a simple observation:
lactose metabolism
• The hypothesis developed by Jacques Monod and Francis Jacob infers that gene
regulation governs lactose metabolism
o Their study looked at 3 different groups with 3 different growth treatments
Treatment
Glucose
Glucose/Lactose
Lactose
Result
No
β-galactosidase
No
β-galactosidase
High production
of
β-galactosidase
o Conclusion of the study: the presence of lactose required to induce
galactosidase production
o Glucose inhibits galactosidase production
o They accomplished this without modern DNA technology, instead they used:
▪ The generation and study of metabolic mutants
▪ Bacterial conjugation and analysis
▪ Logic and deduction
▪ They used replica plating to reveal different classes of metabolic mutants
• Three classes of metabolic mutants emerged:
• lacZ-: cannot cleave indicator molecule even if lactose is present
as an inducer
• lacY-: cells cannot accumulate lactose
• lacI-: cells cleave indicator molecule even if lactose is absent as an
inducer
PaJaMo Experiment
• Using bacterial conjugation to map the lac operon
• Transferring functional lac genes to mutants via conjugation and observing resulting
change
• The order and time needed for each gene to be expressed reveals the relative position
of the lac operon
lac operon
• Operon: group of coordinately regulated genes transcribed as one mRNA sequence
• Promoter: site where RNA polymerase binds and transcription is initiated
