Cell Growth & Control Flashcards
Steps of binary fission
- DNA replication
- Cell elongation
- Septum formation
- Completion of septum with formation of distinct walls
- Cell separation
4 phases of prokaryotic growth
- Lag phase
- Exponential phase
- Stationary phase
- Death phase
What happens in the lag phase
- Cell prepare for growth
- Gene expression
- Synthesis of certain macromolecules
when does exponential phase occur
When cells are adapted to their environment & are growing optimally
In what phase do genetic/biochemical experiments occur at
The exponential phase
What is happening during the stationary phase
- No increase in cell mass/cell number
- Cell growth & death happening at the same time
What is stationary phase caused by
- Essential nutrient supplied by medium is exhausted
- Waste products from metabolism build up to inhibitory levels
Why does death phase occur
- Nutrients deplete
- Toxic metabolic waste products increase
Will serial dilutions differentiate between alive & dead cells
Serial dilutions will differentiate between alive & dead cells as only viable cells will grow
Natural human defences that control microbial growth
- Enzyme lysozyme in both tears & saliva
- Lysozyme cleaves peptidoglycan in bacterial cell walls
environmental effects on microbial growth (5)
- Nutrients
- Temp
- pH
- Water activity
- O2 availability
Max growth temperature
Temperature above which denaturation occurs
3 cardinal temperatures
- Max growth temp
- Min growth temp
- Optimum temp
Optimum temp
Enzymatic rxns occurring at maximal possible rate
Psychrophiles
Low temperature optima
Mesophiles
Mid temp optima
Most commonly found in humans
Thermophiles
High temp optima
Hyperthermophiles
V high temp optima
Acidiphiles
Organisms live at low pH (acidic pH)
Alkaliphiles
Organisms that live at high pH (basic pH)
does water flow into or out of normal prokaryote and why
- Water flows into the cell
- As water diffuses from an area of high water con to an area of low water conc
- Prokaryotic cell has a higher solute conc than environment so water flows in to balance
Halophiles
Like high salt conc
What kind of heat sterilisation is most effective
Moist heat
Conditions to kill endospores
- Autoclave
- Temp of 121 degrees
- 15 mins
Aim of pasteurisation
Kill all pathogenic bacteria in the solution
Flash pasteurisation vs ultrahigh temperature pastuerisation
Flash: 71 degrees for 15 sec
Ultrahigh: 135 degrees for 1-2 sec
How does radiation kill microbes
- Absorbed by DNA
- DNA damage
- Pyrimidine dimerisation
- Microbial death
