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genetics > chapter 12 part 2 > Flashcards

chapter 12 part 2 Flashcards

1
Q

where does allolactose bind to the lac repressor

A

allosteric domain

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2
Q

the formation of the inducer-repressor complex alters what?

A

DNA-binding domain of the repressor and prevents it binding the operator

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3
Q

when allolactose binds to the repressor, what is removed

A

negative control (repression)

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4
Q

2 requirements for lac activity

A
  1. lactose present
  2. glucose absent
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5
Q

will glucose or lactose be used first?

A

glucose

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6
Q

positive control mechanism with glucose and lactose

A

catabolite repression

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7
Q

what do high levels of glucose inhibit?

A

adenylate cyclase (AC)

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8
Q

what does AC convert ATP to

A

cAMP

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9
Q

cAMP binds to what?

A

catabolic repressor protein (CAP)

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10
Q

what does the Crp-cAMP complex bind to

A

lac promoter

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11
Q

what happens when the Crp-cAMP complex binds to the promoter

A
  • strengthens RNA pol interaction
  • physically distorts CAP binding region to expose major grooves
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12
Q

what does bending the DNA at the lac promoter do?

A

exposes major grooves and allows RNA polymerase to bind efficiently

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13
Q

I-

A

unable to bind to operator

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14
Q

Is

A

super repression - unable to bind inducer

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15
Q

Z-

A

no functional B-galactosidase

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16
Q

Y-

A

no functional permease

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17
Q

A-

A

no transacetylase

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18
Q

Oc

A

fail to bind repressor protein - continuous transcription

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19
Q

P-

A

fails to bind RNA polymerase

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20
Q

complementation analysis is carried out in _________ _________ produced by conjugation between F’ (lac) and F- bacteria

A

partial diploids

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21
Q

constitutive mutants

A

certain mutations where genes are transcribed continuously whether or not lactose is available

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22
Q

lac- cells

A

unresponsive to the presence of lactose

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23
Q

genetic mapping of constitutive mutants localizes them to the _____ and ______ regions

A

lacO and lacI

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24
Q

lać operator mutations are exclusively _______-acting

A

cis

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25
Q

cis-acting

A

influence transcription of genes on same chromosome

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26
Q

what is cis-acting typical of

A

DNA sequence mutations that don’t code for proteins
- DNA binding sites

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27
Q

lacI produces a regulatory protein that is ________-acting

A

trans

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28
Q

trans-acting

A

capable of diffusing and interacting with both operators in a partial diploid

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29
Q

what is trans-acting typical of

A

protein mutations

30
Q

non-inducible operon

A

Z and Y genes aren’t expressed, even in presence of lactose

31
Q

what does the non-inducible operon mutation cause

A

allosteric domain to be altered so that allolactose can’t bind to it

32
Q

super-repressor mutation

A

non-inducible - allosteric domain altered so allolactose can’t bind to it

33
Q

what does the operator overlap with

A

the promoter

34
Q

the repressor bending physically interferes with what?

A

RNA polymerase binding

35
Q

what does the tetrameric repressor bind to?

A

O1 and O3

36
Q

what does binding of the tetrameric repressor to O1 and O3 induce

A

DNA loop formation that brings O1 and O3 close togehter

37
Q

the loop structure includes part of the promoter and blocks what?

A

access by RNA polymerase

38
Q

Oc mutations

A

disrupt the two-fold symmetry of the O1 segment
- DNA loop can’t form, RNA pol can bind to promoter

39
Q

is the tryptophan operon involved in anabolic or catabolic pathways

A

anabolic

40
Q

feedback inhibition

A

activity of the end product blocks transcription of the operon

41
Q

the tryptophan operon is ___________ and _________

A

repressible and attenuated

42
Q

attenutation

A

can fine-tune transcription to match the immediate needs of the cell

43
Q

what does the trp operon contain

A
  • five structural genes
  • regulatory region with promoter (trpP) and operator (trpO)
  • leader region (trpL)
  • attenuator region
44
Q

5 structural genes of trp operon

A

E, D, C, B, A

45
Q

the sixth gene outside the trp operon encodes what?

A

trpR protein - repressor protein that is activated when bound to trp

46
Q

tryptophan acts as a _________ by binding to the trp repressor and activating it

A

co-repressor

47
Q

what happens when trp is absent

A

repressor protein can’t bind to operator allow for transcription of operon

48
Q

when does the trp operator turn on

A

when there is no tryptophan present - makes trp

49
Q

what happens when trp is present

A

activated repressor binds to trp O and prevents transcription of the operon
- turns off production of trp

50
Q

true or false: trpR- cells are produce trp constitutively

A

false - trpR- strains have higher rates of operon transcription in the presence of trp than trpR+ strains, but not 100%

51
Q

what is attenuation controlled by

A

162-bp trpL region

52
Q

what does the trpL region contain

A

4 repeat DNA sequences
- mRNA produced contains complementary repeats and start/stop codons for a 14 amino acid polypeptide

53
Q

what can the four repeat sequences form

A

different stem-loop structures

54
Q

among the codons for the short polypeptide of trpL are 2 what?

A

back-to back codons for tryptophan
- sensors for availability of trp in cell

55
Q

what are the sensors for the availability of trp in the cell

A

2 back-to-back codons

56
Q

what 2 stem-loop structures are central to attenuation?

A

3-4 and 2-3
- 1-2 plays minor role

57
Q

3-4 stem loop of mRNA

A
  • termination stem loop - halts RNA polymerase progress along leader region of DNA
58
Q

what is region 4 followed by

A

poly-uracil sequence that function similarly to intrinsic termination of transcription by bacteria

59
Q

what may the 3-4 stem loop be preceded by?

A

1-2 stem loop

60
Q

2-3 stem loop of mRNA

A

antitermination stem loop - forms when region 1 is not available for pairing and thus prevents region 3 from interacting with region 4
- allows RNA polymerase to continue through leader sequence

61
Q

transcription along regions 1 and 2 allows for what to form?

A

1-2 stem loop, and slight pause in transcription

62
Q

what does the slight pause that comes from transcription of regions 1 and 2 allow?

A

ribosome binds to start codon in trpL (translation begins)

63
Q

with adequate supply of trp, codons 10 and 11 are easily translated which leads to what?

A

ribosome moves to the stop codon, partially obscuring regions 1 and 2

64
Q

what happens as a result of the ribosome moving to the stop codon

A

allows regions 3 and 4 to pair, which causes termination of transcription by attenuation

65
Q

without an adequate supply of trp, where does translation stall

A

codons 10 and 11

66
Q

what happens when the ribosome stalls at codons 10 and 11

A

ribosome obscures region 1 and allows regions 2 and 3 to pair

67
Q

what happens when regions 2 and 3 pair

A

creates anti termination conformation, allowing for continued transcription of genes needed for production of trp

68
Q

mutating of one codon 10 and 11 results in what

A

alters attenuator responsiveness to trp

69
Q

mutating both codon 10 and 11 results in what

A

abolishes attenuator’s ability to sense trp

70
Q

mutation of regions 3 and 4 results in what

A

prevents stable binding between them

71
Q

attenuation also represses transcription where?

A

in several amino acid operon systems such as E. coli and Salmonella

genetics (47 decks)

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