The lac operon

what is the lac operon

group of genes involved in lactose metabolism

what does E. coli prefer instead of lactose

glucose

what are the two conditions for lac operon to be expressed

lactose is available

glucose is not available

what are the two regulatory proteins involved

lac repressor (acts as a lactose sensor)

catabolite activator protein (CAP) (acts as a glucose sensor)

3 genes in lac operon

lac Z, lac Y, lac A

what does lac Z do

encodes enzyme B-galactosidase, responsible for splitting lactose into readily usable glucose and galactose monosaccharides

what does lac Y do

encodes a membrane protein called lactose permease which is a transmembrane "pump" that allows the cell to import lactose

what does lac A do

encodes an enzyme known as a transacetylase that attaches a particular chemical group to target molecules. unknown if it actually as any role in lactose breakdown

what is the operator in the lac operon

negative regulatory site bound by the lac repressor protein

what does the operator overlap with

promoter

what is the CAP binding site

positive regulatory site bound by the catabolite activator protein

what does the lac repressor do

represses (inhibits) the transcription of the lac operon

what does the lac repressor bind to

operator

when does the lac repressor bind

when lactose is not available, lac repressor binds to the operator

how does transcription behave when lactose is not present

the lac repressor binds, RNAP cannot move forward (downstream)

how does transcription behave when lactose is present

some lactose transforms into allolactose which binds to the repressor, changing its shape and releasing from the DNA. RNAP can move forward

what is allolactose (2)

isomer of lactose

inducer

inducer

a molecule that causes the expression of a gene to be turned on

what kind of operon is the lac operon

inducible as it is usually. turned off but can be turned on with allolactose present

what does the CAP do

drive high levels of transcription

what does CAP need to bind to DNA

cAMP molecule

when are cAMP molecules produced

in low glucose situations

what is cAMP

cyclic AMP, which is a hunger message produced by E. Coli when glucose is low

glucose is present, lactose not present

repressor is binded, CAP not binded, transcription of operon does not occur

glucose present, lactose present

repressor not binded, CAP not binded, transcription of operon is low

glucose not present, lactose not present

repressor binded, cap binded, transcription of operon is none

glucose not present, lactose present

repressor not binded, cap binded, transcription of operon is high