What is binary fission?
a process of (PROKARYOTIC) asexual reproduction in which a cell grows to twice its normal size and divides in half to produce 2 identical daughter cells with exact same genetic information as parent
Describe the (4) steps in binary fission.
1) cell replicates its DNA, duplicated chromosomes attach to cell membrane
2) cell elongates, pushes 2 identical chromosomes apart
3) contractile ring forms between two chromosomes, new cytoplasmic membrane forms as ring contracts, cell wall septum folds
What is "generation time"?
time required for a bacterial cell to grow and divide; or time required for population of cells to double in number
- varies depending on chemical and physical conditions
- generation time for average bacteria = 1-3 hours
- generation time for E. coli = 2
What are the 4 growth phases of bacteria (in static culture)?
1) lag phase
2) log/exponential growth phase
3) stationary phase
4) death/logarithmic decline phase
Population Growth: Lag Phase
cells are adapting to new environment; synthesizing the metabolic machinery and chemicals required for optimum reproductive potential
Population Growth: Log / Exponential Phase
phase of rapid chromosomal replication, growth, and reproduction; reproductive rate reaches a constant, DNA & protein synthesis are maximized
Population Growth: Log / Exponential Phase
What are the implications for medical science?
- populations in log phase are most susceptible to antimicrobial drugs
- best time for Gram staining procedures due to integrity of cell walls
- often best phase for laboratory and industrial purposes
Population Growth: Stationary Phase
occurs when number of dying cells equals number of cells being produced; growth slows as nutrients are depleted and wastes accumulate
Population Growth: Stationary Phase
What is a CHEMOSTAT?
a mechanism that artificially postpones the onset of stationary phase by continually removing wastes and adding fresh medium; allows log phase to continue indefinitely
Population Growth: Death Phase
occurs when cells are dying at a faster rate than they are produced; may result in entire population death; some cells (esp. spore-forming) can survive indefinitely