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Principles of Molecular Biology > Transcriptional Regulation - Prokaryotes > Flashcards

Transcriptional Regulation - Prokaryotes Flashcards

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1
Q

Why is transcriptional regulation the most common form of regulation?

A

It is the most efficient

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2
Q

What is the major mechanism of transcriptional regulation?

A

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

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3
Q

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

A

Repressor proteins

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4
Q

How do prokaryotes regulate networks of genes?

A

Operons

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5
Q

What are operons?

A

Clusters of genes transcribed as a single transcript

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6
Q

Why do operons allow for regulation of networks of genes?

A

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

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7
Q

Where is the lux operon found?

A

Vibrio fischeri, bioluminescent bacteria

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8
Q

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

A

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

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9
Q

How is the lux operon regulated?

A

By an activator: LuxR

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10
Q

What regulates whether the lux operon activator binds?

A

The amount of autoinducer around

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11
Q

What are autoinducers?

A

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

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12
Q

Why are autoinducers required for the lux operon?

A

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

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13
Q

When does the lux operon get expressed?

A

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

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14
Q

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

A

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

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15
Q

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

A

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

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16
Q

Where is the Lac operon found?

A

E. coli

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17
Q

What is the Lac operon used for?

A

Lactose metabolism

18
Q

How is the Lac operon regulated?

A

With both an activator and a repressor

19
Q

What are the 4 genes in the Lac operon?

A

LacZ, LacI, LacA and LacY

20
Q

What is the function of the LacZ gene?

A

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

21
Q

What is the function of the LacI gene?

A

Encodes for the repressor

22
Q

What is the function of the LacY gene?

A

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

23
Q

What is the function of the LacA gene?

A

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

24
Q

Which of the 4 Lac operon genes is independently expressed?

A

LacI - the repressor

25
Q

What is the activator of the Lac operon?

A

CAP

26
Q

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

A

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

27
Q

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

A

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

28
Q

What is the basal state of a promotor?

A

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

29
Q

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

A

No, it changes depending on the strength of the promotor

30
Q

What is the basal state of the Lac operon?

A

Low transcription

31
Q

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

A

Off

32
Q

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

A

High

33
Q

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

A

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

34
Q

What molecule regulates the activity of the Lac operon repressor?

A

Lactose

35
Q

What molecule regulates the activity of the Lac operon activator?

A

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

36
Q

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

A

Inactive

37
Q

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

A

Active

38
Q

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

A

Inactive

39
Q

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

A

Active

40
Q

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

A

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

41
Q

How much cAMP is present when glucose levels are high?

A

Low

42
Q

How much cAMP is present when glucose levels are low?

A

High

Principles of Molecular Biology (17 decks)

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