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HW ans key_Ch 17 - Ch 17 HW ans key MCQ 1 2 3 4 5 6 7 A B D...

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Ch. 17 HW ans key MCQ: 1) A 2) B 3) D 4) D 5) C 6) C 7) B True/ False: 1) F 2) T 3) F 4) T 5) F 6) F 7) T SQ: 1) The lac operon consists of 3 structural genes; lac Z encodes β-galactosidase, lac Y encodes permease and lac A encodes transacetylase. All 3 are transcribed as a single unit, resulting in a polycistronic mRNA. β-galactosidase cleaves lactose into galactose and glucose and also converts lactose to allolactose. Permease is necessary for the passage of lactose through E.coli cell membrane. All 3 genes have an overlapping promoter and operator region. Upstream of the lac operon is the lacI gene, which encodes the repressor. The repressor binds at the operator region and inhibits transcription by preventing RNA polymerase from binding to the promoter region. When small amount of lactose is present, β-galactosidase converts some of it to allolactose, which binds to the lac repressor. This binding alters the shape of the repressor and reduces its affinity for the operator. If the repressor does not bind to the operator, RNA polymerase can bind to the promoter and initiate synthesis.
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