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Cellular Composition > Control of Gene Expression in Prokaryotes > Flashcards

Control of Gene Expression in Prokaryotes Flashcards

1
Q

Are genes always on or off unless controlled?

A

On

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2
Q

What dictates levels of gene expression?

A

Strength of a promoter

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3
Q

What do repressors bind to?

A

Operators

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4
Q

What does the operator overlap with?

A

RNA polymerase binding sites

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5
Q

Where do activators bind?

A

To sites that do not overlap with RNA binding sites

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6
Q

How do activators help increase gene expression?

A

They help RNA polymerase to bind to the promoter

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7
Q

In the prescence of both glucose and lactose which sugar will a prokaryotic cell use first?

A

Glucose

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8
Q

What is an operon?

A

A unit of genomic DNA that contains a cluster of genes under the control of a single promoter which act together as part of a unified pathway

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9
Q

Give an example of how an activator might work

A
  • in the prescence of a ligand the activator is turned on
  • this makes protein-protein interactions with RNA polymerase which helps binding
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10
Q

Give an example of how a repressor may work

A
  • if ligand is absent the repressor can bind to the operator
  • this means RNA polymerase cannot bind
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11
Q

What negative control mechanism is used by lac operon?

A

Lac repressor

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12
Q

Which positive control mechanism is the lac operon controlled by?

A

CAP-cAMP complex

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13
Q

Which enzyme does lac z code for?

A

β-galactosidase

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14
Q

What does β-galactosidase do?

A

Cleaves lactose into glucose and galactose

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15
Q

What enzyme does lac y code for?

A

β-galactoside permease

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16
Q

What does β-galactoside permease do?

A

It is a membrane bound protein which pumps lactose into the cell

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17
Q

What enzyme does lac A code for?

A

β-galactoside transacetylase

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18
Q

What does β-galactoside transacetylase do?

A
  • Transfers an acetyl group from acetyl-CoA to β-galactosides
  • Activates lac z
19
Q

What is the structure of the lac repressor?

A

Tetramer

20
Q

What is allolactose?

A

A product of metabolism of lactose

21
Q

What occurs to the lac repressor in the prescence of allolactose?

A
  • allolactose binds to the lack repressor
  • Binding of allolactose prevents the lac repressor from binding to the operator
  • RNA polymerase is allowed to bind and transcribe the operon
22
Q

What chemical does CAP sense?

A

cAMP

23
Q

What kind of molecule is CAP?

A

A protein

24
Q

What happens to cAMP levels in the prescence of glucose?

A

They reduce

25
Q

What happens in the cell when glucose levels reduce?

A
  • Adenylate cyclase is activated
  • cAMP levels rise
26
Q

What kind of promoter is the lac promoter?

A

A weak promoter

27
Q

How is the lac operon activated by CAP?

A
  • When glucose levels fall, cAMP levels rise (due to activation of adenylate cyclase)
  • cAMP binds to CAP
  • CAP can then bind to the operon and recruit RNA polymerase
  • produces strong gene expression
28
Q

What is the dormant state of a bacterium infected with a virus called?

A

Lysogenic growth

29
Q

What does the Cro repressor turn off?

A

Expression of the lambda repressor

30
Q

Which operator does the lambda repressor have the highest affinity to?

A

OR1

31
Q

Which operator does the cro repressor have the highest affinity for?

A

OR3

32
Q

What does the lambda repressor turn off?

A

Expression of all phage genes, including the gene for the Cro repressor

33
Q

Which operator does the lambda repressor first bind to?

A

OR1

34
Q

Which operator is nearest to the promoter for the lambda repressor gene?

A

OR3

35
Q

Which operator is nearest to the promoter for the Cro repressor gene?

A

OR1

36
Q

What happens when the lambda repressor binds to OR1?

A

Due to the proximity of OR1 to the promoter for the Cro repressor, it blocks cro expression

37
Q

What kind of binding occurs between lambda repressor molecules on operators?

A

Cooperative binding

38
Q

What occurs when lambda repressor binds to OR2?

A
  • It produces enchanced lambda repressor expression by enhancing RNA polymerase binding
  • Now acts as a lambda activator
39
Q

What occurs when lambda repressor binds to OR3?

A

It blocks lambda repressor expression by blocking binidng of RNA polymerase

40
Q

How does the lambda repressor maintain good levels of expression?

A

It alternates between binding to OR2 and OR3

41
Q

What prompts breakdown of the lambda repressor?

A

The cell entering a stressful situtation e.g. DNA damage

42
Q

What happens when the cell enters a stressful situation?

A
  • The cell produces lots of proteases
  • The lambda repressor is broken down by proteolysis
  • Cro represor is no longer blocked
43
Q

What happens when the cro repressor binds to OR3?

A
  • Blocks lambda repressor expression
  • Allows for the expression of the remaining 50 phages genes
  • Lytic growth occurs

Cellular Composition (15 decks)

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