BSCI 331: Exam 3 - Lac Operon

Lac operon

bacterial gene system controlling lactose metabolism

Lac repressor

protein that binds operator and blocks transcription in absence of lactose

CAP binding site (catabolite activator protein)

activator that binds to DNA with cAMP when GLUCOSE is ABSENT OR LOW when LACTOSE IS PRESENT

Glucose

• initiates metabolic pathway to create ATP and used until maximum till it runs out

• does not synthesize or make genes

Lactose

initiates transcription only when glucose is not present

if GLUCOSE is PRESENT

• won’t make or synthesize genes

• CAP not bound and activated

if LACTOSE is PRESENT

• able to make genes/transcription

• may be able to make genes only if glucose is not present

• binds to Lac repressor which causes conformational change → prevents binding to/from DNA to proceed transcription

• activates CAP when binded to cAMP → becomes “glucose starved” and allows RNA polymerase to move forward and turn operon on

if GLUCOSE is ABSENT

• lactose will be able to proceed with transcription and bind to repressor to cause conformational change and release it from DNA

• CAP gets activated by cAMP to send signal

• Operon will be turned on to move RNA polymerase

if LACTOSE is ABSENT

operon off because Lac repressor is bounded and CAP not bounded siince glucose is present