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GN 421 > Basic Transcription Part 2 > Flashcards

Basic Transcription Part 2 Flashcards

1
Q

operon

A
  • group of contiguous, coordinately controlled genes
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2
Q

inducible gene expression

A
  • certain genes expressed under certain environmental conditions
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3
Q

cells will go on which first

A
  • glucose

- then lactose use lac operon

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4
Q

one strategy to regulate gene expression

A
  • group functionally related genes together
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5
Q

Beta-galactosidase

A
  • used to break down lactose into glucose and galactose
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6
Q

all 3 genes transcribed together from

A
  • 1 promoter to produce

- 1 mRNA = polycistronic mesage

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7
Q

each gene has its own

A
  • ribosome binding site
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8
Q

lacY

A
  • permease

- transports lactose into the cell

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9
Q

LacA

A
  • transacetylase
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10
Q

lac operaton under negative control

A
  • by the lac I repressor
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11
Q

lac I repressor

A
  • tetramer of 4 identical polypeptides
  • binds to operator next to promoter
  • binds to operator and prevents RNA polymerase from binding to promoter and transcribing
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12
Q

repressor is an allosteric protein

A
  • binding of one molecule changes shape of remote site

- allows interaction with a 2nd molecule

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13
Q

inducer

A
  • binds repressor
  • causes change in confirmation and dissociation from the operon.
  • is lactose or allolactose
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14
Q

discovery of lac operon

A
  • certain cryptic mutants expressed B-galactosidase, but could not metabolize lactose
  • add radioactive galactoside to wild type and mutant bacteria
  • only induced wild type took it up
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15
Q

jacob and monod suggest

A
  • substance induced with b-gal to get galactosidase into cells
  • mutants defective in this gene
  • that gene was permease
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16
Q

constitutive mutants

A
  • produced all 3 gene products all the time without induction
  • also not capable of being repressed
17
Q

idea of a repressor

A
  • created merodiploids
18
Q

merodiploids

A
  • partial diploid bacteria
  • had both wild-type (inducible) and constitute alleles
  • wild-type dominant
  • could turn off genes from constitutive and inducible parent
  • wild type produces something that keeps lac genes off unless they are induced
19
Q

predicted the existence of 2 key control elements

A
  • repressor

- operator

20
Q

deletion mutants

A
  • also revealed promoter needed for expression of all 3 lac genes
21
Q

existence of a repressor suggested

A
  • a DNA sequence that binds the repressor

- operator

22
Q

4 types of mutations

A
  • (I^-) - recessive
  • (O^c) - cis-dominant
  • (I^s) - dominant in cis and trans
  • (I^d) - uninducible
23
Q

recessive mutation in the repression (I^-)

A
  • I- mutations make a repressor that cannot recognize the operator
  • mutations that eliminate the function of the repressor are recessive
  • if combined with wild type will make inducible and repressible again
24
Q

operator constitutive mutation (O^c)

A
  • mutations in 1 of operators cause it to be active (unresponsive to repressor)
  • other operator still repressible
  • cis-dominant mutation
25
Q

I^s mutations

A
  • mutation in lac repressor
  • some subunits can bind allolactose some cannot (make unresponsive to inducer)
  • will poison system so neither lac operon will be inducible
  • dominant in both cis and trans
26
Q

I^d

A
  • defect product can form defective tetramers with wild type repressor
  • won’t bind operator
  • no way to repress operon
  • whole tetramer inactive
  • dominant negative (dominant in cis and trans)
27
Q

repressor-operator binding

A
  • add more repressor in presence of inducer - poor binding
  • add more repressor in absence of inducer get increased binding till it levels off
  • repressor binds to operator nicely in absence of inducer
28
Q

O^c lac operator binding to repressor

A
  • binds with lower affinity

- O^c lac operator requires more repressor for binding

29
Q

what activates lac operon

A
  • activation needed only in absence of glucose
30
Q

glucose present

A
  • repression keeps lac operon off
31
Q

as glucose level drops

A
  • cAMP level increases
32
Q

Catabolite activation

A
  • cAMP can activate lac operon even when some glucose is present
33
Q

catabolite activator protein (CAP)

A
  • binds to cyclic AMP
34
Q

map near lac promoter

A
  • at an activator site
  • just upstream of promoter instead of downstream like activator
  • called CAP binding site
  • alpha-CTD of pol binds
35
Q

cAMP and CAP effect on DNA

A
  • cause the DNA to bend

- stabilizes the interaction

36
Q

DNA bending leads to

A
  • induced fit

GN 421 (36 decks)

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