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Lecture 14

Biology 1002B Lecture Notes - Lecture 14: Lac Repressor, Operon, Allolactose

Course Code
BIOL 1002B
Patrick Mc Donald

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Biology 1202 B
Lecture Cycle 7 (Lecture 14)
Regulation of Gene Expression
Material Covered – Lac and trp Operons, Eukaryotic Regulation,
What Determines Cell Function in a Eukaryote?
All cells have the same complement of DNA
- Yet cells of dierent type are vastly dierent
Dierence are not a result of dierent DNA
- Dierent expression of the same set of genes
- Dierences are a result of gene expression (primarily transcrip"on) – further regulatory
mechanisms beyond transcrip"on
Regula"on is more complex in eukaryotes an
Prokaryotic Gene Regulation
Tend to be single celled and rela"vely simple
- Short genera"on "mes – no complex development
React and adapt to changes in environment
- Manufacture the simple products needed for (brief) survival and reproduc"on
Depending on what is available they turn on/o various biochemical pathways
Linked transcrip"on/transla"on of “operons.
The Operon
Operon – Cluster of genes and the DNA sequences involved in their regula"on
- E. Coli Lac Operon – Lactose metabolism which converts lactose to glucose/galactose.
Glucose is preferred sugar – turned on when glucose not available but lactose is.
Operon named a5er operator discovery
- Short sequence which controls genes next to it
Repressor binds operator
- Controls lacZ, lacY, and lacA transcrip"on
- Transcribed as single mRNA – translated together – individual proteins

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Operon: Lactose Absent
Lac repressor binds operator most of the "me
- Nega"ve Control
- Bound repressor prevents polymerase from binding promoter
- Repressor occasionally comes o operator – basal level of lac operon transcrip"on
Lac Operon: Lactose Present, Glucose Absent
Inducible operon (allolactose is inducer)
- Short lived mRNA (3 mins) – control
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