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mcrb 265 > regulation of gene expression > Flashcards

regulation of gene expression Flashcards

1
Q

microbe response

A

microbes respond immediately to enviro changes

  • chemotaxis: movement towards fuel or light source
  • facultative aerobe: switch from O2 to alternate e-acceptor
  • temperature change - increase or decrease in unsaturated FA in membrane
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2
Q

how pathogens signal pathogenesis

A

express virulence factors to establish infection

- express genes to establish symbiont-host relationship

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3
Q

gene expression in prokaryotes

A

start @ promotor
stop @ terminator
RNA polymerase creates single mRNA transcript form stuff in the middle

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4
Q

polycistronic mRNA

A

one transcript encodes multiple polypeptides; ORF separated by stop codons + intercistronic regions of varying length

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5
Q

what are polycistronic genes

A

high gene density on DNA. some genes read forward, others in reverse. tighlty regulated

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6
Q

RNa polymerase, promoter + sigma factor recognition sites

A

need RNA pol+ sigma factor together to read off rna.

diff sigma factors interact w rna pol to get diff sequence from same/similar mrna strand

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7
Q

what is probnow box?

A

10 nucleotides form start. from -10 to -35 sigma + holoenzyme start trasncribing from

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8
Q

process of transcription

A

RNA pol + sigma factor come together at promoter region.
- sigma recognizes promotoer + initiation site
- trxn starts, sigma released. RNA chain grows to termination
- chain stops
- release polymerase and RNA
= once RNApol moves down, another guy can hop on at same time

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9
Q

transcription termination

A

DNA contains inverted repeats
- complementary base-pair stem-loop inhibits continuation of trxn.
physical interference with movement of RNA pol

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10
Q

coupled trxn and translation

A

both in cytoplasm. as RNa strand formed, ribosomes hop on and synthesize protein.

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11
Q

polysome:

A

translation of single mRNA by several ribosomes

= rapid turn on/off. exponential synthesis

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12
Q

4 ways of regulating activtiy

A
  1. constitutive expression - no control
  2. metabolic or posttranslational control of enzyme activity
  3. regulation of enzyme synthesis at translation
  4. regulation of enzyme synthesis at transcription
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13
Q

regulation of enzymes

A

posttranslational
- direct control of enzyme activtiy
- rapid
allosteric regulation

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14
Q

regulation of transcription

  • operon
  • structural genes
  • operator
  • promoter
  • regulator
A

operon: genetic element that controls synthesis of several proteins in prokaryotes

structural genes that encode polypeptides

operator: starts/halts txn by binding protien factors
p: bind RNapol for txn

R: encodes single protein (green circle) which binds to operator to control gene expression

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15
Q

negative transcriptional regulation

A

block mRNA synthesis

  • enzyme overly abundant
  • activity no longer necessary or detrimental to cell
  • involves “repressor protein” to bind DNA and block RNApol
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16
Q

positive transcriptional regulation

A

stimulate mRNA synthesis

  • more enzyme needed in cell
  • activator protein bind to DNA and promote transcription
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17
Q

what are constitutive genes?

A

housekeeping

- no regulation

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18
Q

repressible genes

A

expression stopped when product not needed

- level of enzyme decreases in presence of repressor and co-repressor

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19
Q

inducible genes

A

expressed only when need arises
b-galactosidase induced when glucose is gone, lactose is present
- catalyze lactose hydrolysis to galactose and glucose
- level of enzyme rises in presence of repressor and inducer

20
Q

negative control - enzyme reduction ex: arginine added to e.coli on media.

A

enzyme for argninine shut down to conserve energy. arginie corepressor to prevent own synthesis.

21
Q

what is corepressor

A

repressor cannot bind operator alone. corepressor needed to bind to repressor to bind to operator. once bound no more synthesis

22
Q

negaative control: enzyme induction

A

e.coli growing on substrate other than lactose.

lactose added = enzymes induced + transcribed.
- de novo enzyme synthesis

23
Q

how lactose presence = enzyme induction

A

repressor bound at operator of lac operon.

lactose = inducer: binds to repressor causing its removal, txn allowed

24
Q

positive control

A
  • activator protein promotes binding of RNA polymerase promoter
  • non-continuous operons involved
  • inducer molecule required for activator to bind DNA
  • maltose is inducer
25
Q

catabolite repression

A

expression of genes to metabolize non-preferred sugar are repressed due to lack of catabolite (cyclic AMP). want to use preferred substrate first. non-preferred second.

26
Q

what is diauxic growth?

A

glucose metabolized first

  • gene expression for lactose metabolism turns on B-galactosidase
  • lag during switch in gene expression and de novo enzyme synthesis. biphasic growth curve.
27
Q

transcription of lac operon onlly occurs when?

A

glucose levels are low AND lactose is present

28
Q

Catabolite activator protein + lac operon?

A

CAP - bind to site upstream ofpromoter in lac operon to stimulate transcription (+regulator)
CAP bound to catabolite, cAMP, to be active.

glucose transport inhibits cAMP synthesis and lactose transport
catabolite repression lifted by adding caMP to media

29
Q

lac operon under both positive and negative control

A

CAP binds to cAMP = cap-cAMP dimer.
bind to lac operon increases binding of RNA polymrase at promoter
- txn of lac genes begins
-lactose required as inducer to remove repressor protein bound at operator (negative control of lac operon)

30
Q

summary of lac operon regulation

A
  1. Lactose, no glucose. repressor inactive, CAP–cAMP stimulates txn
  2. galactose + glucose. allolactose take off repressor. cAMP levels too low to activate CAP no trxn
  3. no lactose, no glucose. both activator and repressor are active. no trxn
  4. glucose, no lactose. no caMP and repressor block txn
31
Q

CAP as global regulator

A

regulates several operons under control of different catabolites

  • arabinose, galactose, maltose, + other carbon sources.
  • each operon under control of negative regulators too.
  • some features differ for each operon, binding by CAP-cAMP is same
32
Q

what is regulon

A

multiple operons responding to common regulatory protein - CAP operon. all the stuff that CAP moderates

33
Q

good things about global regulation

A

multiple operons allow bacteria to quickly adjust to changing enviro

34
Q

what happens when alternate sigma factors are produced?

A

sigma factor = nutrient deprivation, creates spore.

global effects
= cell differentiation
= tolerance to abrupt temp changes
= increase in osmolarity

35
Q

e. coli regulons

A

O2 both +/-, [caMP], temp, -NH3
oxygen radical
damaged DNA

36
Q

two-component regulatory systems and phosphorelay

A

two component signals link external events to regulation of gene expression
- transfer of phosphoryl group from one protein to another

37
Q

signal transduction

  • sensory kinase
  • response regulator
A

sK: respond to enviro signal “effector molecules”. become phosphorylated

RR: phosphorylated by sensor kinase. becomes activator of gene expression. dephosphorylated by phosphatase enzyme

38
Q

OmpF/OmpC porin proteins

A

f - wider diameter than c= more nutrients through.
C protects against bile salts
f - used when osmotic pressure is low.
c when osmotic pressure is high

39
Q

regulation by two component signal transduction, envZ for OmpF repression

A

EnvZ - sensor kinase - sense increase in osmolarity. autophosphorylates and passes phosphoryl group to OmpR, the response regulator
- ompR-P can bind to DNA to repress ompF and activate ompC expression

40
Q

quorum sensing

A

regulation in response to cell density. regulated by autoinducer.
-> diffusible signaling, molecule in membrane: acetyl homoserine lactone (AHL)
found in g- bacteria, species specific, and synthesized in cell and diffused out.

triggers cascade - binds to regulator (enhancer) quorum binds to operator to recruit polymerase. lux increases. shift from none to lots of transcription when there are a certain number of cells

41
Q

lux operon

A

cells glow due to luciferase enzyme.
= bioluminescent bacteria.
encodes AHL synthase.
luxR(activator) binds AHL (inducer) and positively regulates expression of lux genes = bioluminescence

42
Q

best studied bacterium for bioluminescence

A

vibrio fischeri. luminescence takes place only at hgih cell density when quorum sensing genes are induced.

43
Q

bacterial communications

A

cross-talk, “eavesdrop”, sensing, signaling molecules.
= stop cross talk may be antimicrobial drug source? no signal that enough cells to trigger infection = no onset of infection

44
Q

antisense RNA

A

transcribed from opposite DNA strand of mRNA.
- base pair with mRNA to prevent translation,(+) control or degrate RNA.

regulate synthesis from synthesized RNA

45
Q

translational control: riboswitches

A

g(-) bacteria
= regulate translation of mRNA
- absence of ligand, mRNA forms stem-loop and access to binding sequences (shine-dalgarno). in presence of ligand, diff interaction = diff stem-loop no access to ORF (shine-dalgarno)

mcrb 265 (14 decks)

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