Mutant A: Lacl has a mutation in its DNA binding site such that it cannot bind t
ID: 90063 • Letter: M
Question
Mutant A: Lacl has a mutation in its DNA binding site such that it cannot bind the operator Mutant B: Mutation affects the protein that produces CAMP such that CAMP is produced at a high level all the time. Indicate the expression levels of beta-galactosidase in Mutant A and Mutant B Indicate with +, ++, or - only. +: Expression occurs (low level) ++: Expression occurs (high level) -: No expression almost no expression FYI: Wild type cells in the case of "neither glucose nor lactose" still produce a small amount of beta- galactosidase because Lacl is not always bound to the operator. Although Lacl stays bound to the operator most of the time, sometimes it falls off and allows transcription to take place for a short amount of time.Explanation / Answer
lacI gene (regulatory gene for lac operon) produces a protein that blocks RNAP from binding to the promoter of the operon. because of muatation in lacl gene it can not bind to lac operon and thus may not block RNAP to bind to promoter and allow the production of beta galactosidase. the lac operon allows for the effective digestion of lactose when glucose is not available
Mutation A produces -galactosidase thus cleaves lactose, a disaccharide, into glucose and galactose
mutation B The lac repressor always expressed unless co-inducer binds to it. In other words, it transcribed only in the presence of small molecule co-inducer. In the presence of glucose, the catabolite activator protein (CAP), required for production of the enzymes. Binding of RNA polymerase to the promoter is aided by the cAMP-bound catabolite activator protein. thus high level of cAMP enhances the effect of binding of RNA polymerase to the promoter thus allowing RNAP to transcribe the lac genes and thereby leading to higher levels of the encoded proteins. thus cleaves lactose, a disaccharide, into glucose and galactose.
Condition in cell
Lactose
Glucose only
Glucose and lactose
Neither glucose or lactose
Wild type
++
-
-
+
Mutation A
-
++
+
-
Mutation B
-
++
-
-
Condition in cell
Lactose
Glucose only
Glucose and lactose
Neither glucose or lactose
Wild type
++
-
-
+
Mutation A
-
++
+
-
Mutation B
-
++
-
-
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