Lac Operon

Question 1

Promoter

Answer 1

Site where enzyme RNA polymerase attaches and moves along DNA to transcribe the genes.

Question 2

Operator

Answer 2

Where lac repressor protein attaches via a complementary shaped binding site.

Question 3

Beta Galactosidase

Answer 3

Digests lactose into galactose and glucose.

Question 4

Lactose Permease

Answer 4

Makes bacterial cell more permeable to lactose.

Question 5

When lactose is absent

Answer 5

Genes switched off. Lac repressor binds to operator, which blocks active site of promoter. RNA polymerase unable to bind to promoter, so genes not transcribed into mRNA and enzymes not synthesised.

Question 6

When lactose present

Answer 6

Genes switched on. Lac repressor binds to lactose changing its shape so can’t bind to operator. RNA polymerase can bind to promoter. Genes are transcribed into mRNA and the two enzymes are synthesised so can break lactose down.

Question 7

Advantages

Answer 7

Saves energy. Amino acids saved for vital proteins. No waste of space from unnecessary proteins.