Lecture 15 and 16 Flashcards
Information is the result of…
Processing, manipulating and organising data
How to change prokaryotic gene expression?
Change the RNA polymerase sigma factor
What does changing the RNA polymerases sigma factor do?
Directs polymerase to different promoters
What does normal sigma factor do?
sigma-70 binds to RNA polymerase and recognizes sequence in promoter to initate transcription
What happens when sigma factor 70 is heated?
heat shock disables it
What happens when heat shock disables sigma factor 70?
rpoH gene product, sigma 32, binds to sequence in promoter of heat shock gene and starts transcription
What is negative control of prokaryotic gene expression?
Repressor protein(s) bind to DNA and inhibit transcription
What is positive control of prokaryotic gene expression?
Activator protein(s) bind to DNA and enhance transcription
What genes have a level of encoded protein that vaires?
Regulated genes
What genes are switched off until required?
Inducible genes
What genes are switched on until not required?
Repressible genes
What genes encode a constant amount of protein?
Constitutive genes
How were lactose utilization genes identified?
Complementation analysis of mutants
Who isolated Lac- mutants unable to utilize lactose?
Jacob, Monod et al.
What three genes were identified as lactose utilization genes?
LacZ, lacY, lacA
What experimental evidence was there for a repressor protein for the lac genes?
Isolated mutant in lacI gene which synthesised lac permease in absence of lactose–> lacI is repressor
How is enzyme synthesis of lac genes triggered?
Inducer causes B-galactosidase synthesis
How does the inducer work
It binds to repressor so repressor cannot bind DNA
What type of effect is the inducer having on the repressor?
Allosteric effect
What is an operon?
two or more genes co-ordinately regulated by a single promoter and terminator
What is an operator?
A section of DNA that binds to regulator protein in an operon
List the sites in order.
Regulator gene (lacI)
Promoter
Operator
LacZ
What does lacZ code for?
B-galactosidase
What does lacY code for?
Permease
What does lacA code for?
Transacetylase
How does lacI work as a regulator gene?
It codes for repressor protein which binds to operator, lactose binds and inactivates it
When glucose is scarce and lactose is present, what levels are high?
cAMP
cAMP binds to what to make what?
Inactive CAP
Active CAP
What type of control increases lac gene transcription using CRP bound to regulatory region?
Positive control
What happens if there are changes in the operator?
Repressor cannot bind, lac enzymes synthesised constitutively
What is a trans effect?
Genes are regulated even when two DNA segments are not physically adjacent
What is a cis-acting element?
A DNA segment that must be adjacent to the genes it regulates
What do trans acting elements do?
Diffuse through cytoplasm, act as target DNA sites on any DNA moleule
What can cis acting elements do?
Only influence expression of adjacent genes on the same DNA molecule
Do eukaryotes have operons?
no
What affects expression in eukaryotes?
Chromatin
What are 4 regulatory protein types in eukaryotes?
Activators
Coactivators
Basal transcription factors
Repressors
What do activators do?
Bind to genes at enhancer sites, determine which genes are switched on and increase speed
What are coactivators?
Adaptor molecule that integrate signals from activators
What do basal transcription factors do?
Position RNA polymerase at the start of the protein-coding region of a gene
What do repressors bind to in eukaryotes?
Silencer sites on genes
