Operons

Genes regulated in…

response to life cycles and environmental conditions

Genes need the ability to

turn off and on again

Housekeeping genes

required for basic cellular function are conitnously expressed and continously transcribed and translated

Operon

a functionla cluster of genes found mostly in bacteria and archeaea that share a single promoter and are transcribed into a single mRNA strand

What do operons do

allows cells to turn related genes on or off

What do operons consist of

an operator, a promoter and a cluster of genes

What do operons also contain and what it do

They contain regulatory DNA sequences, is a non coding reigon of that controls timing, location and level of expression of genes, they also control transcriotion

example of a regulatory DNA sequence

a promoter

Operators in operons

the segment of DNA located between the promotor and structural genes that acts as an on/off switch for gene transcrotion

Repressors

repressor protein binds to the operator to block RNA polymerase from moving forward with transcription

Activators

proteins that bind to the operator to allow transcrition to continure

Regulatory proteins

come from regulatory genes, can be turned on or off by specifc molecules, examples are activator and proteins

E. coli

bacteria that mainly metabolizes glucose, but if there is none, it will use lactose

lac operon

genes that must be expressesd to metabolize and use lactose

what genes do lac operon have

lacZ, lacY and lacA

promoter in lac operon

RNA polymerase binding site

Operator in lac operon

negative regulator site bound by the lac repressor site

CAP

catobolite activator protien that binds to CAP site in lac operon, allowing RNA polymerase to transcipt

When lactose is absent…

Lac repressor binds to the operator, preveint the RNA polymerase from transcripting

WHen lactose is there and glucose is absent

Allolactose (rearraged lactse) binds to the lac repressor, making it let go of the operator allowing RNA polymerase to transcripit

Inducer

small molecule that triggers expression of a gene/operon

When there is low glucose…

cAMP is procued (cyclic AMP) and attaches to CAP, allowieing it to bind to DNA. CAP in turn helps RNA polymerase bind to promoter resulting high levels of transcription

When there is high glucose…

no cAMP made so CAP can’t bind to DNA, transcription occurs only at a level

cAMP (cyclic AMP)

is a regulatory protein that acts as a “hunger signal” when glucose levels are low

Trypothan

amino acid that e coli needs, trp operon allows the production of this

Corepressor

molecule that helps turn off the expression of genes by binding to reprssor, when tyrpthatn levels are high, trypothan acts as a corepressot stoop the expression to trp operon genes

wehn trypothan levels are low

trp repressor becaomes inactive and, aloowing for expression fo trp operon genes