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genetics > chapter 12 part 2 > Flashcards

chapter 12 part 2 Flashcards

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Biology 101 flashcards
1
Q

what are the two requirements for activity?

A

lactose must be present, glucose must be absent

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2
Q

what happens when glucose is high?

A

very little transcription of lac operon

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3
Q

what happens when glucose is low?

A

transcription is enhances. lots of transcription

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4
Q

what happens when glucose is absent?

A

catabolite repression (positive control mechanism)
-glucose will be used first even if lactose is present

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5
Q

what do high levels of glucose inhibit?

A

adenylate cyclase (AC)

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6
Q

what does AC convert to?

A

cAMP

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7
Q

what does cAMP bind to?

A

catabolic repressor protein (crp)
-this creates the Crp-cAMP complex which binds to the Lac Promoter

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8
Q

what is crp also known as?

A

CAP

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9
Q

what is crp transcribed from?

A

the crp gene

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10
Q

what happens with +lactose/-glucose relating to CAP and cAMP?

A

CAP-cAMP bidning to the Lac promoter strengthens RNA polymerases interaction with the Lac promoter
-CAP-cAMP binding physically distorts the CAP binding region located immediately upstream the Lac Promoter
-bending of the DNA exposes the major grooves in the Lac promoter allowing RNA pol to bind efficiently
-leads to high levels of transcription in lac operon

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11
Q

I-

A

repressor is unable to bind to operator

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12
Q

Z-

A

no function beta galactosidase

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13
Q

I^s

A

so called super repressor. unable to bind the inducer (allolactose), blocking transcription

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14
Q

Y-

A

no functional permease

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15
Q

A-

A

no transacetylase

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16
Q

O^c

A

fails to bind repressor protein, resulting in continuous (constitutive) transcription

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17
Q

P-

A

fails to bind RNA polymerase or does so weakly

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18
Q

what is complementation analysis carried out in?

A

partial diploids produced by conjugation between F’ (lac) & F- bacteria

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19
Q

what is the F’ copy of the operon unable to produce and what about the other copy?

A

a functional permease (lacY-) & the other copy is unable to prouduce functional beta-galactosidase (Lacz-)
-in combination, the mutations carried by each copy of the operon complement because the wild-type allele of each gene is dominant to the mutant allele

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20
Q

what are constitutive mutants

A

where genes are transcribed continuously whether or not lactose is available

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21
Q

what do other mutants (besides constitutive) do?

A

cause cells to be unresponsive to the presence of lactose, & therefore lac-

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22
Q

are lac operon mutations cis or trans

A

cis-acting- they influence transcription of genes only on the same chromosome

23
Q

is the lac+ that produces a regulatory protein cis or trans acting?

A

trans-acting
-is capable of diffusing & interacting with both operators in a partial diploid

24
Q

non-inducible operon

A

the Z & Y genes are not expressed, even in the presence of lactose
-causes the allosteric domain to be alterd so that allolactose cannot bind to it; the I^s (for the super-repressor) mutation is dominant to the
-cells are unresponsive to the presence of lactose

25
Q

what do O^c mutations do?

A

disrupt the two-fold symmetry of the O1 segment
-the DNA loop cannot form, & RNA polymerase can bind the promoter & initiate transcription

26
Q

operator & repressor interactions

A

the operator overlaps w the promoter, allowing repressor binding to physically interfere with RNA polymerase binding
-tetrameric reporessor bind to O1 & O3 & induced DNA loop formation that bring O1 & O3 close together

27
Q

what does the loop structure include?

A

part of the promoter & blocks access by RNA polymerase

28
Q

the tryptophan operon is ____________ and ____________ andd it is responsible for what?

A

is repressible & attenuated
-the production of tryptophan

does not exactly say the work blanks in the slide

29
Q

is tryptophan operon catabolic or anabolic?

A

anabolic - operate through activity of end product to block transcription of the operon - feedback inhibition
-repressible operons

30
Q

what do repressible operons have as a second regulatory capability?

A

attenuation- which can find-tune transcription to match the immediate needs of the cell

31
Q

what does tryptophan act as?

A

a co-repressor by binding the trp repressor & activating it

32
Q

what happens when trp is absent

A

the repressor cant bind to operator, allowing for transcription of the operon
-turning ON the production of tryptophan

33
Q

how many structural genes does the trp operon contain?

A

5

34
Q

what are the protein products of the five structural genes in the trp operon?

A

trpE, trpD, trpC, trpB, & trpA

35
Q

what does the regulatory region of trp contain?

A

a promoter (trpP), operator (trpO), leader region (trpL) that contains the attenuator region

36
Q

what contains the attenuator region?

A

leader region (trpL)

37
Q

what does the sixth region (outside the operon) encode for?

A

the trpR protein, a repressor protein that is activated when bound to trp

38
Q

when the is trpR region activated?

A

when bound to trp

39
Q

what happens when trp is present?

A

activated repressor binds to trpO & prevents transcription of the operon
-turning OFF the production of tryptophan

40
Q

what is the second mechanism for controlling trp operon expression?

A

attenuation- controlled by the 162 bp trpL region

41
Q

how many dna repeat sequences trpL region contain?

A

4

42
Q

what can the four repear sequences of trpL region form?

A

different stem loop structures (1,2,3,4)

43
Q

what are the back to back codons among the codons for the short polypeptide called?

A

“sensors” for the availability of trp in the cell

44
Q

what are the two stem-loop structures that are central to attenuation?

A

3-4 stem loop
2-3 stem loop

45
Q

about the 3-4 stem loop

A

termination stem loop
halts RNA polymerase progress along the DNA within the leader regions

46
Q

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

A

formation of a 1-2 stem loop, which can induced a pause in attenuation

47
Q

about the 2-3 stem loop of mRNA

A

antitermination stem loop
-forms when region 1 is not available for pairing & thus prevents region 3 from interacting with region 4

-this allows RNA pol to continue to though the leader sequence & into the structural genes

48
Q

what happens when there is tryptophan in abundance

A

transcription across regions 1 & 2 allows for the 1-2 stem loop to form & a slight pause in transcription is just long enough for a ribosome to bind to the start codon trpL (translation begins)

49
Q

what does transcription across regions 1 & 2 allow for?

A

the 1-2 stem loop to form & a slight pause in transcription & a ribosome binds to that start codon in trpL

50
Q

about codons 10 & 11

A

they are trp codons
-have an adequate supply of trp
-easily translated
-ribosome moves to the stop codon, partially obscuring regions 1 & 2
-allows only regions 3 & 4 to pair- causing termination of transcription attenuation

51
Q

what happens without an adequate supply of trp

A

translation stalls at codons 10 & 11
-ribosome obscured region 1, allowing regions 2 & 3 to pair
-creates antitermination conformation, allowing for continued transcription of genes needed for production of trp

52
Q

what allows for continued transcription of genes needed for production of trp?

A

antitermination conformation

53
Q

what else does attenuation repress

A

transcription in several amino acid operon systems in bactera
ex: e. coli & salmonella

54
Q

what can reduce the efficiency of the attenuation mechanism

A

if codons 10 and 11 (the sensors) are mutated to produce different amino acids
if there are mutations of regions 3 & 4, which prevents stable binding between them

genetics (37 decks)

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