Prokaryotic gene expression

Question 1

what is the lac operon

Answer 1

genes in bacteria that produce b-galactosidase which is needed for the breakdown of lactose in glucose and galactose

Question 2

when does transcription of the b-galactosidase gene occur

Answer 2

when lactose is present the gene for b-galactosidase is turned on

Question 3

what happens when lactose is NOT present in the bacteria’s environment

Answer 3

repressor molecule binds to the operator gene
enzyme RNA polymerase cannot bind to the DNA (promotor region) gene is switched off
Transcription cannot occur so mRNA isn’t synthesised
b-galactosidase is not made by translation on ribosomes

Question 4

what happens when lactose IS present in the bacteria’s environment

Answer 4

lactose binds to the repressor molecule
repressor molecule cannot bind to the operator gene
enzyme RNA polymerase can bind to the DNA (promotor region) gene is switched on
transcription of mRNA occurs
mRNA is translated into b-galactosidase
b-galactosidase breaks down lactose into glucose and galactose

Question 5

how do you know if the gene that produces b-galactosidase is switched on

Answer 5

chemical ONPG is broken down by b-galactosidase
if ONPG is broken down then galactose and ONP will be produced
colour change will occur

                                                   b-galactosidase
                                    ONPG    -----------------------    galactose  +   ONP
                                  colourless)                                                    (yellow)