Regulation of Gene Expression

Question 1

What is a Gene?

Answer 1

A segment of DNA which codes for a single polypeptide (protein)

Question 2

What is a Polycistrionic mRNA?

Answer 2

A single mRNA molecule that codes for several gene products in bacteria

Question 3

What is an Operator?

Answer 3

A specific region of the DNA near the promoter of a gene, required for the transcriptional control of that promoter

Question 4

What is an Operon?

Answer 4

A number of adjacent genes transcribed as a polycistrionic mRNA

Expression may be subject to common control mechanism

Question 5

What is an Operon?

Answer 5

A number of adjacent genes transcribed as a polycistrionic mRNA

Expression may be subject to common control mechanism

Question 6

What controls the amount of mRNA synthesis?

Answer 6

Repressor proteins synthesised from a regulator gene

Question 7

What is the function of the Lactose Operon?

Answer 7

Breakdown of disaccharide lactose into the monosaccharides galactose and glucose

Question 8

What enzyme does the Lactose Operon use to break down lactose?

Answer 8

β-Galactosidase

Question 9

Which bond does β-Galactosidase cleave?

Answer 9

1-4 bond

Question 10

Which genes make up the Lac Operon?

Answer 10

• LacZ
• LacY
• LacA

Question 11

What does the LacI gene produce?

Answer 11

Repressor

Always produced & not part of the Lac Operon

Question 12

What does the LacI gene produce?

Answer 12

Repressor

Always produced & not part of the Lac Operon

Question 13

What does the LacZ gene produce?

Answer 13

β-Galactosidase

Question 14

What does the LacY gene produce?

Answer 14

Permease

Question 15

What does the LacA gene produce?

Answer 15

Transacetylase

Question 16

What is the function of Permease?

Answer 16

Brings lactose products into the cell

Question 17

What is the function of Transacetylase?

Answer 17

Function not known

Question 18

What happens to the lac operon when there is NO inducer (lactose) present?

Answer 18

• Repressor binds to operator, preventing passage of RNA polymerase.
• No transcription

Question 19

What happens to the lac operon when the inducer (lactose) IS present?

Answer 19

• Inducer binds to repressor and prevents it from binding to operator
• Transcription takes place

Question 20

How does the repressor bind to the operator for transcription of the Arg Operon?

Answer 20

Requires a co-repressor (argenine) present

RNA polymerase transcribes Arg Operon while arginine concentrations are low

Question 21

How does the release of the co-repressor (arginine) affect the Arg Operon?

Answer 21

Blocks transcription of Arg Operon when arginine concentrations are high

Question 22

How are Inducible operons affected by their gene products?

Answer 22

Switched ON

Question 23

How are Repressible operons affected by their gene products?

Answer 23

Switched OFF

Question 24

What type of transcription control mechanism are Induction & Repression?

Answer 24

Negative control

Question 25

How does Positive Control initiate transcription at the promoter?

Answer 25

An activator protein is required to activate RNA polymerase instead of repressor protein

Question 26

What operon uses Positive Control to transcribe its genes?

Answer 26

Maltose Operon

Question 27

Why is an activator protein required in Positive Control for transcription?

Answer 27

RNA polymerase is unable to recognise the target promoter without it

Question 28

How does a Transcriptional Activator work?

Answer 28

Bends DNA in order to aid the RNA polymerase in recognising the -10 and -35 recognition points on DNA