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APS 138: Molecular and cell biology > Lecture 8: Regulation of Prokaryotic Gene Expression 1 > Flashcards

Lecture 8: Regulation of Prokaryotic Gene Expression 1 Flashcards

1
Q

Transcription leads to

A

-mRNA degradation
or
-translation –> protein processing & degradation

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2
Q

Prokaryotic genes are often organised in

A

functional operons

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3
Q

prokaryotic cell function operon description:

A 
Promoter region
-5' end 
-RNA polymerase attaches
-operator 
Functional genes
-Gene A,B&C 
-3' end
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4
Q

Prokaryotes:

A

bacteria / archaea

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5
Q

Transcription direction:

A

5’ —> 3’

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6
Q

Gene operons are often controlled by

A

activators or repressors

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7
Q

Activators and gene operon:

A

POSITIVE REGULATION

  • Activator protein binds to promoter region on operon. Stimulates movement of RNA polymerase. Genes are transcribed.
  • Activator kicks back of RNA polymerase. Choppy to the left
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8
Q

Activators and gene operon: if activator gene is not in sufficient quantity or is faulty

A
  • if faulty is degraded

- RNA polymerase is not stimulated & transcriptional induction of operon is prevented

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9
Q

Repressors and gene operon:

A
  • NEGATIVE REGULATION
  • If the repressor protein is not in sufficient quantity then the operon is expressed.
  • as promoter binding site is free & RNA polymerase pathway is not blocked.
  • choppy to the right
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10
Q

Repressors and gene operon: in sufficient quantity

A

If the repressor gene is in sufficient quantity then it binds to the binding site on promoter and block the route of polymerase RNA

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11
Q

Lac Operon what type is it

A

negative regulation; using repressor.

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12
Q

Lac operon as example:

NO LACTOSE PRESENT IN GROWTH MEDIUM

A

-repressor binds to promoter binding site and RNA polymerase pathway is blocked - transcription does not occur

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13
Q

Lac operon as example: LACTOSE PRESENT IN GROWTH MEDIUM

A

Lactose binds to repressor and this causes it to change shape, meaning it can no longer bind to site on operator region. RNA polymerase pathway is clear so genes are transcribed

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14
Q

Lac operon 3 genes:
Lac Z
Lac Y
Lac A

A

Lac Z = Beta-galactosidase
Lac Y = permeate
Lac A = transacetylase

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15
Q

what does beta-galactosidase do?

A
  • mediates hydrolysis of lactose
  • Lactose –LacZ–> H2O + D-galactose + D-Glucose
  • ..so induced production of LacZ reduces lactose concentration which represses induction of the Lac operon
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16
Q

The Lac operon is under

A

negative feedback regulation

17
Q

Lac operons negative feedback loop:

A
  • -> Lactose inhibits LacI repressor
  • -> Lac operon is expressed
  • -> b-galactosidase activity reduces lactose levels
  • -> Lac I repressor becomes active
  • -> Lac operon expression is blocked
  • -> Lactose levels increase
  • -> –> –>
18
Q

Trp operon in E.coli uses a

A

repressor

- negative regulation

19
Q

example Trp operon:

A
  • Repressor gene trp codes for an inactive repressor protein trpR
  • meaning RNA polymerase pathway is not blocked transcription occurs.
  • Genes transcribed produce tryptophan synthesis protein complex –> tryptophan
  • tryptophan binds to inactive repressor protein trpR, changes shape of repressor molecule
  • repressor binds to promoter region and blocks RNA polymerase pathway. –> no transcription
20
Q

trp operon is under

A

Negative feedback regulation

21
Q

negative feedback loop for trp

A

1) the trpR repressor is inactive
2) the trp operon is expressed
3) Tryptophan biosynthesis increases
4) Tryptophan binds to trpR repressor
5) Trp operon expression is blocked
6) Tryptophan biosynthesis decreases
AND REPEAT.. the trpR repressor is inactive…etc

22
Q

Example: Quorum sensing in bacteria

- at low cell density:

A

1 bacterial cell, few auto-inducer compound (often homoserine lactone).

-causes individual behaviours

23
Q

Example: Quorum sensing in bacteria

High cell density:

A

Many bacterial cells & auto-inducer compound (often homoserine lactone)

Causes group behaviours such as:

  • Virulence
  • Microfilm formation
  • Luminescence
24
Q

Quorum sensing occurs in:

A

Aliivibrio fischeri

25
Q

Aliivibrio fischeri produce what at high cell density but not at low cell density

26
Q

Bioluminescence is controlled by the

A

LuxCDABEG operon

27
Q

example animal for quorum sensing:

A

Euprymna Scolopes (the Hawaiian bobtail squid) due to Alivibrio Fischeri

28
Q

Example quorum sensing at low A. fischeri density

A
  • LuxR & LuxI are constantly transcribed
  • Homoserine lactone is secreted
  • Homoserine lactone levels do not build up
  • No binding of LuxR to Lux box (operon)
  • No transcription of lux operon
29
Q

Example quorum sensing at high A. fischeri density

A
  • LuxR & LuxI are constantly transcribed
  • Homoserine lactone is not sufficiently secreted
  • Homoserine lactone levels build up in cell, some from the environment
  • Binding of LuxR to lux box as homoserine has corrected shape of LuxR so they are now compatible
  • Transcription of Lux operon
  • LUMINESCENCE

APS 138: Molecular and cell biology (15 decks)

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