Question

Match the protein listed below with the gene that encodes it or with the DNA sequence within the lac operon where it binds: lac repressor (encoded by...) [Choose] lac repressor (where it binds...) [Choose ] B-galactosidase [Choose] Lactose permease [Choose] Galactoside transacetylase [Choose] CAP [Choose] lacz lacy lacl Operator CAP site lacA

Answer 1

Name of the protein	Where it binds to
Lac repressor is encoded by	lacI The lac operon is comprised of a group of genes under a single promoter that codes for 3 different enzymes. The lacI gene encodes the lac repressor. When lactose absent the lac repressor binds tightly to the operator and inhibits transcription by RNA polymerase. When lactose is present, the lac repressor is unable to bind DNA and as a result transcription proceeds.
Lac repressor binds to	The operator It is a segment of DNA where the repressor binds. When lactose is present the lac repressor cannot bind to the operator, but the repressor can bind to the operator in the absence of lactose and can inhibit transcription.
Beta-galactosidase	This enzyme is encoded by lacZ gene. The β-galactosidase enzyme helps in the cleavage of lactose to glucose and galactose
Lactose permease	lacY The lactose permease protein is encoded by lacY gene. Lactose permease is membrane protein that helps in the cellular transport of lactose inside the cell.
Galactoside transacetylase	lac A The enzyme switches the conversion of lactose into its active form allolactose.
CAP	CAP site Catabolite activator protein (CAP) binds to cAMP and activates transcription of the genes encoded by the lac operon with the aid of RNA polymerase. When glucose is present the cAMP is low and CAP will not be able to bind to cAMP, therefore, no lac mRNA will be formed. Alternatively when glucose is absent there is plenty amount of lac mRNA as the level of cAMP is high and it will be able to bind to the CAP .