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MAKING DECISION :!?: :confused: :question: (REGULATION OF TRANSCRIPTIONā¦
MAKING DECISION :!?: :confused: :question:
REGULATION OF TRANSCRIPTION INITIATION :glass_of_milk:
GENES
INDUCIBLE GENES
genes that code for inducible enzyme
needed only in certain environment
beta-galactosidase
sporulation enzymes
CONSTITUTIVE GENES
expressed continuously by the cells
housekeeping genes
EX: LACTOSE OPERON (LAC OPERON)
Promoter
lacO - operator
lacZ - encode beta-galactosidase
lacY - encode lactose permease
transfer lactose inside bacterial cell
lacA - encodes galactoside transcetylase
PREDICT EXPRESSION OF BETA-GALACTOSIDASE
beta-galactosidase - break down lactose into galactose + glucose
regions that control expressions
LacO - negative control
promoter
beta-galactosidase gene
expressed highly : only lactose / no glucose
expressed a little bit : lactose +glucose
NEGATIVE CONTROL
REPRESSOR ACTIVITY
Lac repressor
tetramaer form and bind to operator
form a loop -> bend DNA
prevent RNA polymerase from binding to promoter
encoded by LacI
not part of the operon
LacI sit upstream of the Lac operon
expressed by a different promoter, but is always expressed
beta-galactosidase side reaction
adjust the bond of lactose: from 1-5 Carbon to 1-6 C
isomerize allolactose
allolactose concentration - lower than lactose
allolactose - act as inducer - bind to repressor + take repressor away from operator
how was lac operon induced in the first place
beta-galactosidase is expressed at a low level
allolactose exist in high sugar/ lactose present environment but at very low level
CATABOLITE REPRESSION
regulation of transcriptions by both repressors and activators
diauxic growth
biphasic growth pattern
prefer to use one carbon source aka glucose over another aka lacotse when both are available
lag occur
after glucose is exhausted
bacterial growth resume when second source is used
catabolite repression play a role in this pattern of growth
OCCUPANCY STATE OF LAC OPERON
no lactose/ no glucose
repressor on operator
no transcription of beta-galactosidase
no lactose/ with glucose
repressor on operator
no expression of beta-galactosidase
with lactose/ no glucose
repressor is removed from operator thanks to allolactose
cAMP bend the DNA sequence
maximize the transcription of beta-galactosidase
with lactose/ glucose
low amount of beta-galactosidase is produced
glucose has to be used first
SIMILAR OPERONS
POSITIVE CONTROL
overview
response to concentration glucose
allows preferential use of glucose
regulated by CAP - catabolite activator protein
CAP helps recruit RNA polymerase
CAP
cyclic AMP receptor protein/ catabolite activator protein
two forms
active form - when cAMP is bound
inactive form - when it is free of cAMP
CAP-cAMP binds to the upstream site where RNA polymerase binds / enhance RNA polymerase to bind
CAP is modulated by cAMP
if no lactose - it doesn't matter whether glucose is present or absent
cAMP
cAMP - 3',5'-cyclic adenosine monophosphate
levels depends on
phosphoenolpyruvate (PE-P)
glucose present - PE-P transfers a phosphoryl group to glucose
last step of glycolysis PEP :arrow_right: pyruvate
little glucose - PE-P transfer phosphoric group to adenyl cyclase
adenyl cyclase is phosphorylated & synthesize cAMP
sugar phosphotransferase system
adenyl cyclase - only active when there's little glucose
HOW THEY MAKE DECISIONS
SENSING THE ENVIRONMENT
QUORUM SENSING
TWO COMPONENT SIGNAL TRANSDUCTION
ALTERATION OF DNA SEQUENCES
TRANSCRIPTION INITIATION
CONTROL OF mRNA STABILITY
TRANSLATIONAL CONTROL
SENSING THE ENVIRONMENT
REGULATORY SYSTEMS / later exam
IMPORTANCE
set of proteins govern pathway
sensor kinase
cell membrane protein w/ extracellular receptor - environmental signal
activate itself by phosphorylation on a
His
residue
response-regulator protein
present in cytoplasm
transfer phosphate from sensor to Asp residue
DNA binding protein
activator - enhance transcription
repressor - inhibits transcription unless needed
found in all three domains of life
PORIN PROTEINS
examples
OmpR
regulate transcription of porin proteins
OmpC
high osmoslarity
smaller porin protein
lower permeability
lower levels of diffusion
dominant when E.coli is in high osmolarity intestinal tract
a loop is formed :arrow_right: OmpF not expressed
OmpR bind to C1 C2 C3 :arrow_right: OmpC expressed
OmpF
low osmolarity
larger porin protein
dominant in dilute environment
more diffusion
affinity of binding F >>> C
depending on osmolarity
porin protein located in the outer membrane
response regulator protein
phosphorylated - has high binding affinity to F1 & C1
not phosphorylated
the upstream regulatory regions of OmpF & OmpC determines their expression
Env Z
sensor kinase
high osmolarity - autophosphorylates more OmpR
low osmolarity - dephosphorylate OmpR
located in inner membrane
gram (-) bacteria have porin to
transfer molecules into periplasmic space
get nutrients
QUORUM SENSING
DIFFERENCE IN BACTERIA
Gram -
vibrio fischeri
AHL
diffuse freely across the cell envelope
reach high concentration inside cell only if many cells are nearby
bind to activator protein LuxR
encoded by LuxI
trigger lux gene transcription
called autoinducer molecule - acyl homoserine lactone
Gram +
Staphylococcus aureux
secrete small peptide - damage host cells/ alter immune system
AIP
autoinducing peptide
control small peptide secretion
activate several proteins that lead to production of virulence proteins
Lux OPERON
DESCRIPTION
fond in vibrio discheri/ allivibrio fisheri
bacteria live freely
or in symbiosis with Hawaiian bobtail squic
cells emit light (luciferase) when present in the light organ of the squid
Lux gene make luciferase, luciferase catalyze this reaction, making light
flavin mononucleotide + O2 + aldehyde ->
GENE REGULATION
lux I - autoinducer
luxC - activates acyl group with AMP
luxD - diverts fatty acids to bioluminescence process
lux A: alpha subunit of luciferase
luxB: beta subunit of luciferase
lux E: reduces the acyl group of AMP to form aldehyde
lux G: reduces FMN during the luciferase reaction
luxR: encodes autoinducer- transcription factor
SYMBIOTIC RELATIONSHIP
bacteria communicate with their neighbors
squid provide food and shelter for bacteria
bacteria produce luminescence - reflect moonlight - camouflage squid
bacteria colonize the light organ at night - squid hunt at night
squid pump the bacteria outside during day
PREDICT THE PRODUCTION OF THE LIGHT (refer to the clicker in class)
