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
