Are genes always being transcribed and translated?

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The lac operon.

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Presentation transcript:

Are genes always being transcribed and translated?

Gene Expression Gene expression for all genes falls into one of two categories. 1. constitutive expression – 1. known as housekeeping genes 2. induced expression –

lac Operon lac - lactose operon – promotergene 1gene 2gene 3 operator

lac Operon Bacterial cells mainly use glucose as a source of energy. The lac operon is only turned (on or off?) when glucose is absent, but lactose is present.

lac Operon Operon codes for three enzymes   -galactosidase (lacZ gene) 2. permease (lacY gene) 3. transacetylase (lacA gene)

lac Operon The lacI gene codes for a separate repressor protein.

lac Operon repressor protein (lacI gene) binds to the prevents RNA polymerase from When do you want the repressor to bind / not bind to the operon?

When lactose is absent:

When lactose is present:

lac Operon effector molecule – inducer –

lac Operon Animation lac Operon Animation