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Biology > Control of Prokaryotic Gene Expression - Operons > Flashcards

Control of Prokaryotic Gene Expression - Operons Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Define: Operon

A

Cluster of genes with related functions; consisting of an operator, a common promoter and 2 or more structural genes, controlled as a single unit to produce a single polycistronic mRNA

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2
Q

Negative control

A

Suggests that regulatory gene of operon encodes for a REPRESSOR

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3
Q

Positive control

A

Suggests that regulatory gene encodes for an ACTIVATOR

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4
Q

Inducible system

A
  • Suggests that default state of operon is OFF, but can be turned on in the presence of an INDUCER
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5
Q

Repressible system

A
  • Suggests that default state of operon is ON, but can be turned off in the presence of a CO-REPRESSOR
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6
Q

Negative inducible control

A
  • repressor normally bound to operator, preventing binding of RNA polymerase to promoter; no transcription of structural genes
  • presence of inducer inactivates repressor by altering tertiary structure and making it unable to bind to operator; transcription of structural genes
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7
Q

Negative repressible control

A
  • repressor unable to bind to operator in normal conformation, allowing RNA polymerase to bind to operator; transcription of structural genes
  • presence of co-repressor activates repressor by altering tertiary structure and making it able to bind to operator; no transcription of structural genes
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8
Q

Positive inducible control

A
  • activator unable to bind to operator in normal conformation, preventing binding of RNA polymerase to promoter; no transcription of structural genes
  • presence of inducer activates activator by altering tertiary structure and making it able to bind to operator; transcription of structural genes
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9
Q

Positive repressible control

A
  • activator normally bound to operator, allowing RNA polymerase to bind to promoter; transcription of structural genes
  • presence of co-repressor inactivates activator by altering tertiary structure and making it unable to bind to operator; no transcription of structural genes
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10
Q

What kind of operon is the lac operon?

A

Negative inducible operon

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11
Q

Type of mechanism lac operon is associated with

A

Catabolism

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12
Q

Structural genes in lac operon

A
  • lac Z
  • lac Y
  • lac A
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13
Q

What does lac Z encode for?

A

β-galactosidase

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14
Q

What does lac Y encode for?

A

Permease

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15
Q

What does lac A encode for?

A

Transacetylase

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16
Q

Function of β-galactosidase

A
  1. Hydrolyse lactose into glucose and galactose

2. Isomerise lactose into allolactose (inducer)

17
Q

Function of Permease

A

Allows efficient uptake of lactose into E. coli cells by active transport

18
Q

Function of Transacetylase

A

Transfer acetyl groups from acetyl CoA to β-galactosides to prevent build-up of toxic products formed by β-galactosidase

19
Q

Promoter of structural genes of lac operon

A

Lac P

20
Q

Operator of lac operon

A

Lac O

21
Q

Regulatory gene of lac operon

A

Lac I

22
Q

What does lac I encode for?

A

Active lac repressor

23
Q

(-ve) Regulation of lac operon - absence of lactose

A
  • regulatory gene, lac I, constitutively transcribed to produce lac repressor
  • active lac repressor binds to operator, preventing RNA polymerase from binding to promoter, lac P; no transcription of structural genes and lac operon is OFF
24
Q

(-ve) Regulation of lac operon - presence of lactose

A
  • some lactose molecules enter E. coli cells aided by permease, before being converted to allolactose, an inducer, by β-galactosidase
  • allocatose binds to repressor, inactivating it by altering tertiary structure and making it unable to bind to operator
  • RNA polymerase binds to promoter; transcription of structural genes and lac operon is ON
25
Q

(+ve) Regulation of lac operon - presence of lactose and glucose

A
  • metabolise glucose preferentially; glucose imported cell, inactivating permease and preventing uptake of lactose
  • genes involved in metabolising other sugars are repressed through catabolite repression
  • glucose inhibits adenylyl cyclase and thus reduces conversion of ATP into cyclic adenine monophosphate (cAMP); fewer cAMP-CAP complexes formed
  • inactive CAP unable to bind to CAP binding site; decreased binding efficiency of RNA polymerase and thus reduced transcription of structural genes
26
Q

(+ve) Regulation of lac operon - presence of lactose, absence of glucose

A
  • no inhibition of adenylyl cyclase by glucose and thus conversion of ATP into cyclic adenine monophosphate (cAMP); cAMP-CAP complexes formed
  • active CAP binds to CAP binding site; increased binding efficiency of RNA polymerase and thus increased transcription of structural genes
27
Q

Regulatory mechanism ensuring lac operon is OFF in presence of glucose

A
  1. Low affinity of RNA polymerase for promoter

2. Glucose-sensitive regulatory mechanism; CAP and CAP binding site

28
Q

What kind of operon is the trp operon?

A

Negative repressible operon

29
Q

Type of mechanism trp operon is associated with

A

Anabolism

30
Q

Structural genes in trp operon

A
  • trp E
  • trp D
  • trp C
  • trp B
  • trp A
31
Q

Regulatory gene of trp operon

A

Trp R

32
Q

What does trp R encode for?

A

Inactive trp repressor

33
Q

Regulation of trp operon - high levels of tryptophan

A
  • tryptophan, co-repressor, binds to inactive trp repressor, activating it by altering tertiary structure
  • trp repressor binds to operator, preventing RNA polymerase from binding to promoter; no transcription of structural genes
34
Q

Regulation of trp operon - low levels of tryptophan

A
  • inactive trp repressor unable to bind to operator, RNA polymerase binds to promoter; transcription of structural genes

Biology (14 decks)

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