BIOL 142 Lecture Notes - Lecture 15: Cyclic Adenosine Monophosphate, Replica Plating, Bacterial Conjugation
Tuesday, April 17, 2018
BIOL 142
•B-galactosidase is synthesized when lactose is present but glucose isn’t."
•Presence of lactose is required to induce galactosidase production"
•Glucose inhibits galactosidase production"
•Replica plating reveals different classes of metabolic mutants"
•3 classes of mutants emerged:"
•lacZ- : cannot cleave indicator molecule even if lactose is present as an inducer"
•lacY- : Cannot accumulate lactose"
•lacI- : 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 each gene to be expressed reveals the relative
position on the operon."
•Operon - group of coordinately regulated genes transcribed as one mRNA"
•Promoter - site where RNA polymerase binds and transcription is initiated"
•Operator - site where repressive element binds"
•The lacI gene is always expressed (always produced)"
•The lac operon falls under the influence of both positive and negative gene
regulation"
•Negative regulation:"
•Lactose absent, repressor present - repressor binds to DNA and stop the
polymerase from moving forward, transcription is blocked"
•Lactose present, repressor present - lactose binds to the repressor and releases it
from the operator, transcription occurs"
•No repressor present, lactose present or absent - the RNA polymerase has a weak
affinity for the promoter and transcribes inefficiently on its own - the system also
requires positive regulation to work efficiently"
•Positive regulation:"
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