C5 Flashcards
What system use by bacteria to control the production of virulence factor
Two complement regulatory system
2 complement system allow to regulate metabolism in response to environmental factors such as
- Temperature changes
- Changes in pH & oxygen availability
- Changes in nutrient availability
2 complement system involved mechanism of
- Cell receive signal from environment
- Transmit it to specific target to be regulated
Define signal transduction
External signal not transmit directly to regulatory protein but detect by sensor that transmit it to regulatory machinery
Parts of signal transduction
- Sensor kinase: cell membrane
- Response regulator protein: cytoplasm
Explain sensor kinase
- Detect signal from environment & phosphorylate themselves (auto phosphorylation) at specific histidine residue
- Sensory kinase also called histidine kinase
Explain regulatory system
- Phosphoryl group transfer to response regulator
- DNA binding protein that regulates transcription which function as activator or repressor
- Must have a feedback loop to complete the control mechanism
Explain feedback loop in 2 complement system
- Involves phosphatase that remove phosphoryl group from response regulator protein
- In many systems, this reaction carried out by response regulator
Define global regulators
Regulatory mechanisms that respond to environmental signal by regulating the expression of many different genes
Explain global regulators
- Called global control system
- Include set of operon & regulon in chromosome but all coordinately controlled
Example of global regulators response
- Catabolite repression
- Stringent repression
What is catabolite repression
- Occur when cell grown in medium containing more than one substrate
- Substrate which is a better carbon & energy source would repress the use of other substrate
Why catabolite repression also called the glucose effects
- Glusoce was the first substance shown to initiate response
- Protein of lac operon, include beta galactosidase required for using lactose & induce its presence
Explain the mechanism of glucose in catabolite repression
- When glucose present, lac operon is not expressed
- When glucose absent, lac operon expressed & cell growth on lactose
Two exponential growth phases in catabolite repression are called
Diauxic, diauxie or diphasic growth
Catabolite repression transcription controlled by
- cyclic AMP receptor protein (CRP)
- CAP (catabolite activator protein)
Explain mechanism of CAP
- Gene encode for catabolite repressible enzyme expressed only if CAP bind to DNA in promoter region
- Allow RNA polymerase to bind to promoter
- CAP only bind if there’s cAMP
Relationship between cAMP & glucose
- Glucose inhibit synthesis of cAMP & stimulate transportation of cAMP out the cell
- Glucose present: level cAMP low, CAP & RNA polymerase cannot bind, catabolite repression
Direct cause of catabolite repression is
Decrease in cAMP level
Why catabolite repression considered a mechanism of global control
- When glucose is the preferred energy source, catabolite repression prevent other expression
- Many other open effected such as lactose, maltose
Explain flagella synthesis controlled by catabolite repression
- Controlled gene for synthesis of flagella
- If bacteria have good carbon source, there is no need to swim around
Define stringent response
Mechanism where gene are regulated to depleted nutrient level in the environment
Explain stringent response
- Found in bacteria & chloroplast when nutrient excess or when cell starved
- When a culture transfer from rich to poor medium with a single carbon source
- synthesis of rRNA & tRNA stopped
Explain the course of stringent response event
- When biosynthesis new amino acid activated, new protein must be made to synthesised amino acid no longer in the environment
- rRNA synthesis began but remain downgraded
Types of nucleotide that triggers stringent response
- ppGpp
- pppGpp
- ReIA
- SpoT
Explain mechanism of stringent response
- When AA limited, pool of uncharged tRNA increase
- Uncharged tRNA insert to ribosome during protein synthesis
- Ribosome shut down & lead to synthesis of ReIA using ATP
- Adding 2 phosphate group from ATP to GTP/GDP to produce pppGpp or ppGpp
- Protein Gpp convert pppGpp to ppGpp
How pppGpp & ppGpp inhibit rRNA & tRNA synthesis
- Binding to RNA polymerase
- Prevent initiation of transcription
Explain mechanism by addition of ReIA & SpoT in stringent response
- Addition of ReIA & SpoT help trigger stringent response
- SpoT protein make or degrade pppGpp or ppGpp
- SpoT also synthesis pppGpp/pppGpp in response to stress or shortage of energy
- Result when absent of precursor of protein synthesis & lack of energy
Define quorum sensing
Process of cell-cell that allow bacteria to share information about cell density & adjust gene expression
Function of quorum sensing
- Virulence
- Conjugation
- Biofilm formation
- Sporulation
What molecule that induce activity of quorum sensing
- Autoinducers
- Diffuse freely across cell envelope
- When many cell make the autoinducer, it accumulates & reach high conc inside cell
- Once they reach threshold level, it bind to regulatory protein & activate transcription
Example of autoinducer
- Acyl homoserine lactones (AHL)
- AI-2: Gram -
- Short peptide: Gram +
Explain heat shock protein
- Bacteria response to high temperature
- Mostly stable but if higher temperature, some are less stable & unfold
- Recognised by protease enzyme
What influence heat shock protein
- When cell are heat stressed induce the synthesis of heat protein to assist in damage & recovery
- Most induce by heat, chemical (ethanol) & high dose of ultraviolet radiation
Major class of heat shock protein
- Hsp70
- Hsp 60
- Hsp 10
Function of heat shock protein
- Assisting the folding newly synthesised proteins
- Prevent aggregation of protein
- Recovering protein that partially or completely unfolded
In E.coli heat shock response controlled by
- RpoH: control gene regulation
- RpoE: regulate quality control & envelope integrity
Explain the relationship between RpoH & DnaK in normal temperature
- RpoH degrade by proteases
- Stimulated by binding of DnaK protein to RpoH
- Rate of RpoH degradation depend on level of free DnaK which bind to inactivate RpoH
- In unstressed cell, level of free DnaK high & level of intact RpoH low
Explain the relationship between RpoH & DnaK in high temperature
- Some protein denature & DnaK recognise & bind to the unfolded protein
- DnaK remove from RpoH which slow the degradation rate of RpoH
- More denature protein, low level of free DnaK & high level of RpoH
- When temp normal, RpoH inactivated by DnaK
