Lecture 7: Growth & Cell Division Flashcards
Growth
Orderly increase in quantity of cellular constituents
Lag phase of batch culture growth
Bacteria are preparing their cell machinery for growth
4 Phases of Batch Culture Growh
- Lag phase
- Log phase
- Stationary phase
- Death phase
Log phase of batch culture growth
Growth approximates an exponential curve. Will appear a straight line on a logarithmic scale
Method of continuous growth
Introduction of fresh media (Sometimes ingested food) into a culture flask paired with waste secretion
Stationary phase of batch culture growth
Cells stop growing and shut down their growth machinery while turning on stress responses to help retain viability
Death phase of batch culture growth
Cells die with a “Half-life” similar to that of radioactive decay, a negative exponential curve
Binary Fission
-Cell elongates & increases in volume
-Chromosome duplicates
-Septum forms with FtsZ
-Cell divides
FtsZ ring
-Protein that forms a septum by constricting cells at the center of the bacteria
6 step process with FtsZ
-In new cell FtsZ is depolymerized as Min prevents its reign
-Chromosome segregation, FtsZ reassembles at mid-cell
-FtsZ ring recruits other divisome proteins
-FtsZ leaves division site
-Septation completes
-Starvation: FtsZ sequestered in biomolecular condensates
MinE protein
Restricts Z-ring formation at mid cell often in the new cell to prevent further division
Spore-like cell divison/Bipolar divison
Production of 2 daughter cells
Intracellular offspring production/binary fission of offspring
1 daughter cell comes from mother cell
-In filamentous gram negative
Multiple fission/Baeocyte production
Production of numerous offspring rather than 2
Direct physical measurement of growth
Direct measurement of dry weight, wet weight, volume of cells after centrifugation, counts of number of cells, viable cell count
Direct chemical measurement of growth
Some chemical components of cell measured such as total N, total protein, or total DNA content
Indirect measurement of chemical activity
Measurement of rate of O2 production or consumption or CO2 production & consumption to find the number of metabolically active cells
Turbidity measurement
Determine the total amount of light scattered by a suspension of cels
Tool used to measure turbidity and values
Spectrophotometer to measure optical density (OD), usually around 600nm
Energy production of facultative anaerobes when no oxygen is present
-Sugar to pyruvate
-Fermentation
-Waste organic
Main factors that can impact growth rate
-Medium composition & characteristics (rich or minimal)
-Bacterium species
-Growth conditions (Temp, pH, Salt, Gas availability)
Cons of turbidity measurement
-Limited sensitivity: cannot detect cell densities less than 10^7 cells/mL
-Reads dead and live cells the same
Energy production in anaerobes when there is no oxygen present
-sugars to pyruvate
-fermentation
-waste organic
Energy production of aerobes when oxygen is present
-Sugars to CO2
-Basic pathways + TCA
-O2 is an electron acceptor
Characteristics of log-phase E-coli
-Bigger and longer cell size
-More sensitive to stress
-Active metabolism
-Less condensed nucleoid
-Active ribosomes
-Thinner cell wall (peptidoglycan)
Characteristics of stationary phase E. Coli
-Smaller and shorter cell size
-More resistant to stress
-Less active metabolism
-More condensed nucleoid
-Hibernating ribosomes
-Thicker cell wall
