Lecture 8 Flashcards
Constitutive gene expression
is always expressed
Inducible gene expression
can be turned on/off
Metabolic regulation
controlling types, amount, and activity of cellular proteins
goal: efficient use of available resources
- allows you to compete in the environment
Gene regulation
increase/decrease amount of protein
- slower response
Post-translation regulation
increase/decrease activity of protein
- faster response
example: protein degradation
Reporter genes
code for proteins that are easy to detect and measure
example: green fluorescent protein (GFP)
- 1 way of studying gene expression
DNA sequencing
isolate mRNA from cells, transform mRNA to DNA, and determine identity & number DNA sequences
- 1 way of studying gene expression
Regulatory proteins
proteins that bind to DNA
Homodimeric structure (two identical structures)
Bind in major groove of DNA
Interact with specific DNA sequences
Regulatory proteins function
start/stop transcription
negative control: block RNA polymerase, prevent transcription
positive control: bind RNA polymerase, activate transcription
Negative control
repression of mRNA synthesis
- control DNA region = operator
- located after promoter
Positive control
activation of mRNA synthesis
- control DNA region = activator-binding site
- located before promoter
Enzyme repression (negative control)
repressor (DNA binding protein) + corepressor (binds/activates repressor)
biosynthetic (anabolic) enzymes
Enzyme induction
repressor + inducer
degradative (catabolic) enzymes
ex. lac operon
maltose catabolism
maltose breakdown
- mal operon
- maltose activator protein once bound to inducer pushes RNA polymerase
Signal molecules compromise of
internal and external signals
Internal signals
small molecules
enter the cell, directly affect transcription
External signals
large molecules
do not enter the cell, require signal transduction
Quorum sensing
- internal signal molecules
- autoinducers
- population density
autoinducers
- signal molecules (species-specific)
- diffuse freely across cytoplasmic membrane (concentration outside cell = concentration inside cell)
- activate transcription of genes
- produced by bacteria
- can leave cell into environment
Two-component regulatory system
Sensor kinase protein
- Located in cytoplasmic membrane
Response regulatory protein
- located in the cell (cytoplasm)
Sensor kinase
- detects signal
- autophosphorylates
- transfer phosphates
Response regulator
- accepts phosphate
- binds to DNA
- represses transcription
Porin regulation
environmental signal: osmotic pressure
sensor kinase: EnvZ
response regulator: OmpR
activator/repressor
genes regulated through ompF (wide) and ompC (skinny)
Attenuation
- transcription
secondary structures: - form 1– regions 3 + 4 bind
– stem-loop ahead of RNA polymerase
– transcription blocked - form 2– regions 2 + 3 bind
– stem-loop behind RNA polymerase
– transcription proceeds
Tryptophan synthesis
form 1– fast translation
- high amount of Trp
- transcription blocked (trp genes)
form 2– slow translation
- low amount Trp
- transcription proceeds (trp genes)
Riboswitches
prevention of translation
signal metabolite binds directly to mRNA
based on alternative secondary structures of mRNA
secondary structures:
-form 1– regions 1+2 bind
(Shine-Dalgarno unbound & translation proceeds)
-form 2– regions 2+3 bind
(Shine-Dalgarno bound & translation blocked)
Antisense RNA
prevention of translation
- small RNA (sRNA) binds to synthesized mRNA
- double-stranded mRNA = no translation
