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70 genetics > L13 - regulation of prokaryote gene expression > Flashcards

L13 - regulation of prokaryote gene expression Flashcards

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1
Q

define constitutive expression and give examples

A

genes transcribed continuously
genes for routine tasks eg RNA pol, tRNA
(housekeeping genes)

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2
Q

what is meant by regulated expression

A

genes whose products are only needed in response to changes in environment and so their expression is regulated

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3
Q

what is meant by -ve control of transcription

A

involves repressor protein

inhibits transcription

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4
Q

at what stage are most prokaryotic genes regulated?

A

transcriptional regulation

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5
Q

what is meant by +ve control of transcription

A

involves activator protein

promotes transcription

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6
Q

what part of gene do activators/ repressors bind to

A

regulatory sequence

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7
Q

define operon

A

clusters of genes involved in same functions undergoing coordinated Tscription controlled by one shared regulatory region

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8
Q

are operons found in eukaryotes

A

no

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9
Q

what is the lac operon responsible for

A

producing 3 polypeptides needed to use lactose as an energy source

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10
Q

describe structure of lac operon left to right

A

laci promoter – laci– regulatory/promoter region (CAP binding site, promoter sequence, operator lacO) –lacZ – lacY – lacA

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11
Q

what is found in the regulatory/promoter region of the lac operon

A

CAP binding site
promoter
operator

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12
Q

what is laci

A

region that codes for repressor protein

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13
Q

what does lacZ encode and what is its function

A

B galactosidase

breaks lactose into glucose+galactose

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14
Q

what does lacY encode and what is its function

A

lactose permease

involved in lactose uptake

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15
Q

what does lacA encode

A

transacetylase

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16
Q

is laci expressed constitutively or regulated?

A

constitutively

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17
Q

what part of the lac operon does RNA pol bind to

A

promoter

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18
Q

what binds to the CAP binding site

A

CAP-cAMP

19
Q

what binds to lacO (operator)

A

lac repressor protein

20
Q

is laci part of the lac operon? why / why not

A

no

it has its own promoter

21
Q

describe structure of lac repressor protein

A

contains

  • DNA binding domain (that binds to lacO)
  • allosteric domain (that binds the inducer, allolactose)
22
Q

what binds to the DNA binding domain of the lac repressor protein

A

lacO

23
Q

what binds to the allosteric domain of the lac repressor protein

A

the inducer - allolactose

24
Q

what is allolactose?

A

produced in breakdown of lactose

binds to repressor protein

25
Q

what happens in absence of lactose

A
  1. no lactose = no allolactose
  2. lac repressor protein binds to lacO (operator)
  3. transcription prevented
26
Q

what happens in presence of lactose

A
  1. residual B galactosidase produces allolactose from lactose
  2. allolactose binds to allosteric domain of lac repressor protein and changes its shape
  3. repressor protein cant now cant bind to lacO
  4. transcription takes place
27
Q

why is +ve regulation of the lac operon needed

A

the inducer repressor complex isnt sufficient for lactose metabolism

28
Q

describe +ve regulation of the lac operon

A
  1. in absence of glucose cAMP is produced which binds to CAP
  2. CAP-cAMP binds to promoter region (CAP binding region)
  3. stimulates transcription
29
Q

what is CAP

A

catabolite activator protein

30
Q

will expression of the lac operon occur in the presence of glucose?

A

yes but not much , as when glucose is present there is no cAMP so no +ve regulation of the lac operon

31
Q

describe the laci- mutation

A

produces mutant lac repressor protein that cant bind to operator

32
Q

what happens as a result of a laci- mutation

A
  • lac operon constitutively expressed

- B galactosidase always present

33
Q

describe lacO- mutation

A

mutated operator sequence that repressor protein cant bind to

34
Q

what happens as a result of a lacOc mutation

A

lac operon constitutively expressed

B galactosidase always present

35
Q

describe laci ^s mutation

A

mutant repressor protein which allolactose cant bind to

36
Q

what happens as a result of a laci ^s mutation

A

transcription always repressed

37
Q

what is arabinose

A

pentose sugar from plant cell walls released when plant ingested so can be used as C source for E.coli in gut

38
Q

function of araB araA araD

A

breakdown arabinose until it can enter glycolysis

39
Q

function of araC

A

gene for araC protein

40
Q

is araC transcribed constitutively or regulated

A

constitutively

41
Q

what happens in the absence of arabinose

A
  1. araC protein binds to araI and araO2 forming a loop 2. loop prevents RNA pol and CAP-cAMP binding to para
  2. transcription inhibited
42
Q

what happens in the presence of arabinose

A
  1. arabinose binds to araC protein breaking its connection between araI and araO2
  2. loop opens up to straight line
  3. second araC - arabinose complex binds to araI which interacts with DNA pol increasing its affinity for para
  4. promotes transcription
43
Q

describe +ve regulation of arabinose operon

A

CAP -cAMP bind to CAP binding site (when glucose absent) which further increases RNA pol affinity for para

44
Q

how much does arabinose expression increase in the presence of arabinose

A

300x in 3 sec

70 genetics (19 decks)

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