8 terms

11. Difference between repressible and inducible operons and how positive gene regulation can control expression levels.

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operon
unit of genetic function found in bacteria

consists of promoter, operator, and a cluster of genes whos products function in a common pathway

can upregulate or down regulate operon expression
promoter
specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.
RNA polymerase
binds to promoters in bacteria and transcribes the coding regions of the genes?
operator
Regulatory proteins bind here to control expression of the operon.
Repressible Operon
protein that inhibits gene transcription
-In prokaryotes, this protein binds to the DNA in or near the promoter.

when bound to operator, no production of tryptophan

-too much tryptophan present, bounds to repressible operon, which then binds to operator
Inducible Operon
a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on

lactose absent, repressor active, operon off (blocks RNA polymerase from binding to operator)

lactose present, repressor inactive, operon on (RNA polymerase binds to operator)
Positive Gene Regulation
regulatory protein interacts directly with the genome to switch transcription on
What happens when glucose and lactose are present
It prefers glucose; the enzymes for glucose breakdown in glycolysis are continually present.

Only when lactose is present and glucose is in short supply (cAMP level high, Activate CAP) does E. Coli use lactose and only then does it synthesize enzymes necessary for lactose breakdown (lac mRNA synthesized)
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