L11: Regulation of prokaryote gene expression

Question 1

What is the primary mechanism of gene expression regulation in bacteria?

Answer 1

Transcriptional control

Question 2

What are housekeeping genes and why are they important?

Answer 2

Genes required for basic cellular maintenance

Question 3

2 types of transcriptional control & describe them

Answer 3

Positive regulation: Activator protein binds to DNA & activates transcription

Negative regulation: Repressor protein binds to DNA & prevents transcription

Question 4

How does the lac operon respond to the presence of lactose?

Answer 4

It induces transcription by inactivating the repressor protein

Question 5

What is the function of the lac repressor protein?

Answer 5

To prevent transcription of the lac operon

Question 6

What is the significance of the CAP-cAMP complex in the regulation of the lac operon?

Answer 6

It enhances transcription by binding to the promoter region.

Question 7

Function of promotor in the lac operon structure

Answer 7

Binds RNA polymerase & initiates transcription

Question 8

Function of operator in the lac operon structure

Answer 8

Binds lac repressor protein and blocks transcription

Question 9

Structural genes of the lac operon

Answer 9

lacZ, lacY, lacA

Question 10

Function of lac operon proteins

Answer 10

lacZ: breaks down lactose into glucose+galactose AND produces allolactose

lacY: transport lactose into cell

lacA: Encode protein that allow bacteria to use lactose as an energy source

Question 11

Function of lacL gene

Answer 11

Produces lac repressor protein which binds the operator & blocks transcription

Question 12

Inducer compound of the lac operon

Answer 12

Allolactose

Question 13

2 features of the lac repressor protein

Answer 13

1) DNA-binding domain that binds to the operator sequence (lacO)

2) Domain that binds the inducer, allolactose

Question 14

What is allolactose?

Answer 14

Produced by breakdown of lactose by lacZ

Question 15

What role does allolactose play in the regulation of the lac operon?

Answer 15

It binds to the repressor, preventing it from binding to the operator

Question 16

Describe the absence of lactose in lac operon

Answer 16

Lac operon expressed at VERY LOW LEVELS
- when lactose is absent, there is no allolacose in the cell
- lac repressor protein binds to operator (lacO), preventing transcription

Question 17

Describe the presence of lacose in lac operon

Answer 17

Transcription of lac operon is induced
1) b-galactosidase produce allolactose and this binds to lac represspr

2) Formation of allolactose-lac repressor complex alters DNA-binding domain of lac repressor & prevent it binding the operator

Question 18

Describe lacl- mutation

Answer 18

Mutant lac repressor protein can NOT bind to opertor so lac operon constitutively expressed (always ON)

Question 19

Describe lacO^c mutation

Answer 19

Operator sequence mutated, lac repressor protein can NOT bind, so lac operon constitutively expressed

Question 20

Describe lacl^s mutation

Answer 20

Mutant repressor protein cannot bind to allolactose so it always binds to operator, operon always OFF

Question 21

What role does allolactose play in the regulation of the lac operon?

Answer 21

It binds to the repressor, preventing it from binding to the operator

Question 22

What is the arabinose operon and how is it regulated?

Answer 22

It degrades arabinose, where araC forms a DNA loop preventing transcription without arabinose

Question 23

What is the impact of having no arabinose on the expression of the ara operon?

Answer 23

There is no expression of the ara operon

Question 24

What type of mRNA is produced from the lac operon, and what does this imply about its translation?

Answer 24

Polycistronic mRNA, implying coordinated translation of multiple proteins

Question 25

How does the presence of glucose influence the expression of the lac operon?

Answer 25

Glucose decreases the transcription of the lac operon

Question 26

What is the significance of the polycistronic mRNA produced by the lac operon?

Answer 26

It allows for the simultaneous synthesis of multiple proteins

Question 27

How does the araC protein regulate the arabinose operon?

Answer 27

it forms a DNA loop to inhibit transcription without arabinose

Question 28

What is the structure of the lac operon, including its regulatory regions?

Answer 28

Promoter, operator, and CAP binding site

Question 29

How do mutations in the lac operon provide insights into its function?

Answer 29

They reveal the regulatory roles of individual components through altered gene expression

Question 30

What vectors is lac promotor used in?

Answer 30

Plasmid expression vectors

Question 31

Which 3 enzymes does the arabinose operon produce?

Answer 31

araB, araA & araD which break down arabinose

Question 32

Describe the DNA loop model when there is NO ARABINOSE

Answer 32

araC protein binds to aral & araO2 which form a DNA loop to stop RNA pol & CAP-cAMP - preventing expression of the ara operon

Question 33

Describe the DNA loop model when ARABINOSE IS PRESENT

Answer 33

Arabinose binds to araC, breaking DNA loop and RNA pol can transcribe again - A 2nd araC-arabinose complex binds to aral & increases RNA pol affinity to promotor Para - CAP-cAMP binds the CAP binding site & RNA pol binds to promotor to initiate transcription