Lactose digestion in E. coli begins with its hydrolysis by the enzyme galactosidase. The gene encoding galactosidase, lacZ, is part of a coordinately regulated operon containing other genes required for lactose utilization.

Which of the following figures correctly depicts the interactions at the lac operon when lactose is NOT being utilized? (The legend above defines the shapes of the molecules illustrated in the options.)

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{ RNA polymerase Repressor protein Lactose a. b. Promoter C. Promoter d. Promoter Promoter lacz ➖➖➖➖➖➖➖➖➖➖➖➖➖-+--- Structural Genes Operator lacZ --+-‒‒‒‒‒-†‒‒‒‒‒‒ Operator Operator lacy Operator lacz lacY lacA lacA Structural Genes lacA lacy ----+-------+---- Structural Genes lacz lack lack Structural Genes a. b. Promoter C. Promoter d. Promoter Promoter lacz ➖➖➖➖➖➖➖➖➖➖➖➖➖-+--- Structural Genes Operator Operator lacy +++ Structural Genes Operator lacZ Operator lacy lacA lacz lacA lacy ----+-----+--- Structural Genes lacz lack lack lacA Structural Genes a. C. d. Promoter Promoter Promoter Promoter lacz ‒‒‒‒†‒‒‒‒‒--†➖➖➖➖+ Structural Genes Operator Operator lacZ -+-+-+- Structural Genes Operator lacy Operator lacz lacA lacy lacA lacy --------------- lacA Structural Genes lacA lacz + lack fact Structural Genes a. Promoter b. Promoter d. Promoter Promoter lacz ‒‒‒‒†‒‒‒‒‒--†➖➖➖➖+ Structural Genes Operator Operator Operator lacZ lacy -+-+-+---- Structural Genes Operator lacy lacA lacz lacA lacy ----------------- lacA Structural Genes lack + lack fla Structural Genes lacA { RNA polymerase Repressor protein Lactose a. b. Promoter C. Promoter d. Promoter Promoter lacz ➖➖➖➖➖➖➖➖➖➖➖➖➖-+--- Structural Genes Operator lacZ --+-‒‒‒‒‒-†‒‒‒‒‒‒ Operator Operator lacy Operator lacz lacY lacA lacA Structural Genes lacA lacy ----+-------+---- Structural Genes lacz lack lack Structural Genes a. b. Promoter C. Promoter d. Promoter Promoter lacz ➖➖➖➖➖➖➖➖➖➖➖➖➖-+--- Structural Genes Operator Operator lacy +++ Structural Genes Operator lacZ Operator lacy lacA lacz lacA lacy ----+-----+--- Structural Genes lacz lack lack lacA Structural Genes a. C. d. Promoter Promoter Promoter Promoter lacz ‒‒‒‒†‒‒‒‒‒--†➖➖➖➖+ Structural Genes Operator Operator lacZ -+-+-+- Structural Genes Operator lacy Operator lacz lacA lacy lacA lacy --------------- lacA Structural Genes lacA lacz + lack fact Structural Genes a. Promoter b. Promoter d. Promoter Promoter lacz ‒‒‒‒†‒‒‒‒‒--†➖➖➖➖+ Structural Genes Operator Operator Operator lacZ lacy -+-+-+---- Structural Genes Operator lacy lacA lacz lacA lacy ----------------- lacA Structural Genes lack + lack fla Structural Genes lacA