6.1 gene expression in prokaryotes

Question 1

what is the regulation of gene expression in prokaryotes known as?

Answer 1

the regulation of gene expression in prokaryotes is known as the lac operon

Question 2

what does the bacterium E.coli normally metabolise?

Answer 2

the bacterium E.coli normally metabolises glucose

Question 3

in the absence of glucose, what is respired by the cell?

Answer 3

in the absence of glucose, lactose is respired by the cell

Question 4

what is lactose broken down into?

Answer 4

lactose is broken down into glucose and galactose

Question 5

why is lactose broken down into glucose and galactose?

Answer 5

lactose is broken down into glucose and galactose so it can be used in respiration

Question 6

when can lactose only be metabolised?

Answer 6

lactose can only be metabolised when the enzymes β-galactosidase and β-galactoside permease are made

Question 7

when are the enzymes β-galactosidase and β-galactoside permease made?

Answer 7

the enzymes β-galactosidase and β-galactoside permease are only made when lactose is present

Question 8

what is another name for the enzyme β-galactosidase?

Answer 8

another name for β-galactosidase is lactase

Question 9

what is another name for β-galactoside permease?

Answer 9

another name for β-galactoside permease is lactase permease

Question 10

what is the role of β-galactoside?

Answer 10

the role of β-galactoside is to hydrolyse lactose to glucose and galactose

Question 11

what is the role of β-galactoside permease?

Answer 11

the role of β-galactoside permease is to allow lactose to enter the bacterial cell

Question 12

where are the genes that code for these enzymes found?

Answer 12

the genes that code for these enzymes are found on a stretch of DNA known as the lac operon

Question 13

what is an operon?

Answer 13

an operon is a group of genes that function as a single transcriptional unit

Question 14

what genes does the lac operon consist of?

Answer 14

the lac operon consists of structural genes and regulatory genes

Question 15

what do the structural genes code for?

Answer 15

the structural genes codes for the desired protein (enzymes)

Question 16

what does the regulatory gene code for?

Answer 16

the regulatory gene codes for a repressor molecule which switches off/deactivates or promotes a gene

Question 17

what can the repressor molecule bind to?

Answer 17

the repressor molecule can bind to the operator region and to lactose

Question 18

which region does RNA polymerase bind to?

Answer 18

RNA polymerase binds to the promoter region to begin transcription

Question 19

what happens in the absence of lactose?

Answer 19

in the absence of lactose:

1) the lac repressor protein binds to the operator preventing RNA polymerase from binding to the promoter region
2) the repressor protein prevents the gene LacZ and LacY from being transcribed (expressed)
3) the enzymes for lactose metabolism are not made

Question 20

what does the gene LacZ transribe?

Answer 20

the gene LacZ transcribes β-galactoside

Question 21

what does the gene LacY transcribe?

Answer 21

the gene LacY transcribes β-galactoside permease

Question 22

what happens in the presence of lactose?

Answer 22

in the presence of lactose:

1) lactose binds to the lac repressor protein and alters the shape of the protein
2) the change in the shape of the lac repressor protein prevents it from binding to the operator region causing it to unbind
3) RNA polymerase can then bind to the promoter region and begin transcribing the structural genes into mRNA
4) the mRNA sequence is then translated into the two enzymes needed to break lactose down