Transcriptional Regulation - Prokaryotes

Question 1

Why is transcriptional regulation the most common form of regulation?

Answer 1

It is the most efficient

Question 2

What is the major mechanism of transcriptional regulation?

Answer 2

Regulation of the recruitment of RNA polymerase, either by repressing or promoting binding to the promotor

Question 3

What proteins physically block RNA polymerase from binding to stop transcription?

Answer 3

Repressor proteins

Question 4

How do prokaryotes regulate networks of genes?

Answer 4

Operons

Question 5

What are operons?

Answer 5

Clusters of genes transcribed as a single transcript

Question 6

Why do operons allow for regulation of networks of genes?

Answer 6

Since they all work together, transcribing them into a single mRNA mean they are also all regulated together at the same time

Question 7

Where is the lux operon found?

Answer 7

Vibrio fischeri, bioluminescent bacteria

Question 8

What does the lux operon produce? How many genes are there?

Answer 8

5 proteins are expressed. Two make up luciferase, the fluorescent protein, and the other three are fatty acid reductases

Question 9

How is the lux operon regulated?

Answer 9

By an activator: LuxR

Question 10

What regulates whether the lux operon activator binds?

Answer 10

The amount of autoinducer around

Question 11

What are autoinducers?

Answer 11

Small molecules secreted by bacteria that tell other bacterial cells how many there are around

Question 12

Why are autoinducers required for the lux operon?

Answer 12

LuxR can’t bind to DNA unless it is bound to an autoinducer

Question 13

When does the lux operon get expressed?

Answer 13

When there is a lot of autoinducer around at high cell density

Question 14

How much of the lux operon is being transcribed at low cell density?

Answer 14

Transcription is off. There is little autoinducer around, so LuxR can’t bind to DNA to activate transcription

Question 15

How much of the lux operon is being transcribed at high cell density?

Answer 15

Transcription is on. There is a lot of autoinducer, so LuxR can bind to DNA and activate transcription

Question 16

Where is the Lac operon found?

Answer 16

E. coli

Question 17

What is the Lac operon used for?

Answer 17

Lactose metabolism

Question 18

How is the Lac operon regulated?

Answer 18

With both an activator and a repressor

Question 19

What are the 4 genes in the Lac operon?

Answer 19

LacZ, LacI, LacA and LacY

Question 20

What is the function of the LacZ gene?

Answer 20

Encodes for beta-galactosidase, the enzyme that cleaves lactose into glucose and galactose

Question 21

What is the function of the LacI gene?

Answer 21

Encodes for the repressor

Question 22

What is the function of the LacY gene?

Answer 22

Encodes for lactose permease, the transport protein that lets lactose into the cell

Question 23

What is the function of the LacA gene?

Answer 23

Encodes a transacetylase and is involved in side reactions from beta-galactosidase

Question 24

Which of the 4 Lac operon genes is independently expressed?

Answer 24

LacI - the repressor

Question 25

What is the activator of the Lac operon?

Answer 25

CAP

Question 26

Where does the Lac operon activator bind? What does it do?

Answer 26

Binds to the CAP site in the regulatory region of the operon. It helps RNA polymerase bind but their binding sites don't overlap

Question 27

Where does the Lac operon repressor bind? What does it do?

Answer 27

Binds to the operator. It overlaps with the binding site of RNA polymerase and physically blocks it from binding

Question 28

What is the basal state of a promotor?

Answer 28

The level of expression when the gene is not being regulated in any way

Question 29

Is the basal state of a gene the same for every gene?

Answer 29

No, it changes depending on the strength of the promotor

Question 30

What is the basal state of the Lac operon?

Answer 30

Low transcription

Question 31

What is the level of transcription when only the repressor is bound to the Lac operon?

Answer 31

Off

Question 32

What is the level of transcription when only the activator is bound to the Lac operon?

Answer 32

High

Question 33

What is the level of transcription when both the repressor and the activator is bound to the Lac operon?

Answer 33

Off. The repressor is physically blocking RNA polymerase, so it wins out

Question 34

What molecule regulates the activity of the Lac operon repressor?

Answer 34

Lactose

Question 35

What molecule regulates the activity of the Lac operon activator?

Answer 35

Indirect regulation by glucose, which is inversely proportional to the levels of cAMP

Question 36

Is the Lac operon repressor active or inactive when lactose levels are high?

Answer 36

Inactive

Question 37

Is the Lac operon repressor active or inactive when lactose levels are low?

Answer 37

Active

Question 38

Is the Lac operon activator active or inactive when glucose levels are high?

Answer 38

Inactive

Question 39

Is the Lac operon activator active or inactive when glucose levels are low?

Answer 39

Active

Question 40

How does glucose regulate the activity of the Lac operon activator?

Answer 40

It is indirect through cAMP. cAMP binds directly to the activator

Question 41

How much cAMP is present when glucose levels are high?

Answer 41

Low

Question 42

How much cAMP is present when glucose levels are low?

Answer 42

High