chapter 12 part 2 Flashcards by Kaylyn Rhoads

where does allolactose bind to the lac repressor

allosteric domain

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the formation of the inducer-repressor complex alters what?

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

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when allolactose binds to the repressor, what is removed

negative control (repression)

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2 requirements for lac activity

lactose present
glucose absent

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will glucose or lactose be used first?

glucose

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positive control mechanism with glucose and lactose

catabolite repression

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what do high levels of glucose inhibit?

adenylate cyclase (AC)

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what does AC convert ATP to

cAMP

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cAMP binds to what?

catabolic repressor protein (CAP)

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what does the Crp-cAMP complex bind to

lac promoter

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

strengthens RNA pol interaction
physically distorts CAP binding region to expose major grooves

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what does bending the DNA at the lac promoter do?

exposes major grooves and allows RNA polymerase to bind efficiently

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I-

unable to bind to operator

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super repression - unable to bind inducer

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Z-

no functional B-galactosidase

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Y-

no functional permease

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A-

no transacetylase

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fail to bind repressor protein - continuous transcription

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P-

fails to bind RNA polymerase

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

partial diploids

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constitutive mutants

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

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lac- cells

unresponsive to the presence of lactose

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

lacO and lacI

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lać operator mutations are exclusively _______-acting

cis

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cis-acting

influence transcription of genes on same chromosome

what is cis-acting typical of

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

lacI produces a regulatory protein that is ________-acting

trans

trans-acting

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

what is trans-acting typical of

protein mutations

non-inducible operon

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

what does the non-inducible operon mutation cause

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

super-repressor mutation

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

what does the operator overlap with

the promoter

the repressor bending physically interferes with what?

RNA polymerase binding

what does the tetrameric repressor bind to?

O1 and O3

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

DNA loop formation that brings O1 and O3 close togehter

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

access by RNA polymerase

Oc mutations

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

is the tryptophan operon involved in anabolic or catabolic pathways

anabolic

feedback inhibition

activity of the end product blocks transcription of the operon

the tryptophan operon is ___________ and _________

repressible and attenuated

attenutation

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

what does the trp operon contain

- five structural genes - regulatory region with promoter (trpP) and operator (trpO) - leader region (trpL) - attenuator region

5 structural genes of trp operon

E, D, C, B, A

the sixth gene outside the trp operon encodes what?

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

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

co-repressor

what happens when trp is absent

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

when does the trp operator turn on

when there is no tryptophan present - makes trp

what happens when trp is present

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

true or false: trpR- cells are produce trp constitutively

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

what is attenuation controlled by

162-bp trpL region

what does the trpL region contain

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

what can the four repeat sequences form

different stem-loop structures

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

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

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

2 back-to-back codons

what 2 stem-loop structures are central to attenuation?

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

3-4 stem loop of mRNA

- termination stem loop - halts RNA polymerase progress along leader region of DNA

what is region 4 followed by

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

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

1-2 stem loop

2-3 stem loop of mRNA

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

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

1-2 stem loop, and slight pause in transcription

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

ribosome binds to start codon in trpL (translation begins)

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

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

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

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

without an adequate supply of trp, where does translation stall

codons 10 and 11

what happens when the ribosome stalls at codons 10 and 11

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

what happens when regions 2 and 3 pair

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

mutating of one codon 10 and 11 results in what

alters attenuator responsiveness to trp

mutating both codon 10 and 11 results in what

abolishes attenuator's ability to sense trp

mutation of regions 3 and 4 results in what

prevents stable binding between them

attenuation also represses transcription where?

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

chapter 12 part 2 Flashcards

(71 cards)