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Bacterial Growth and Reproduction Kelly Spiller East View High School Georgetown TX 78628
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Definitions Growth in this case means increase in numbers not size Binary fission is the process of cell division of prokaryotic bacteria Daughter cells are the resulting cells of binary fission Generation time is the time for a complete life cycle of a cell from daughter cell to division Plasmid is an extra, usually circular piece of DNA in some bacteria; it often carries genes for resistance
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Four growth phases: # of cells LAG
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Four phases explained Lag – adjusting to new conditions or environment Log – exponential growth; 1,2,4,8,16…. Stationary – depletion of nutrients or accumulation of wastes Death – continued depletion or accumulation
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Four factors that affect growth
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Temperature Temperature: Psychrophiles – optimum growth is at 10 Celsius Mesophiles – optimum is at 25-35 C. Thermophile – optimum is at 60C. Extreme Thermophile – optimum is higher
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pH Acidophile – optimum is acidic conditions Neutrophile – optimum is close to neutral Alkalophile – optimum is basic conditions
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Water and osmotic pressure Prefer saturated conditions Osmotic pressure is based on the concentration gradient. Too high = rupture Too low = shrivel Hypertonic = conc. is higher (must define) Hypotonic = conc. of lower (must define) http://www.youtube.com/watch?v=Ji1wetFn gLo
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Oxygen Obligate aerobes – require O 2 Facultative – can grow with or without but are better with Aerotolerant – can grow with or without but are better without Obligate anaerobe – die in the presence of O 2 Microaerophile – require O 2 but 20% too high Capnophile – require CO 2
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Mechanisms of variation and reproduction http://www.youtube.com/watch?v=7sZ5Nz8_cfc
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Binary Fission Very fast but very low variation in species 1. DNA Replication 2. Cell elongation 3. Cleavage All daughter cells are genetically identical except for mutations which occur at a very low rate.
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Mutation Mutation – random accidental changes in DNA of an individual. May be passed on to daughter cells via binary fission Critical to create diversity to avoid extinction Can be good, bad or no effect http://www.youtube.com/watch?v=eDbK0 cxKKsk
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Conjugation Occurs through the pilus = conjugation tube Extra DNA found in Plasmids can be transferred to cells which lack them Occasionally the tube breaks too early and the entire sequence is not transferred = more variation http://www.youtube.com/watch?v=EtxkcS GU698
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Transformation DNA can be “picked up” by cells from the environment Increases variation but not new cells Griffith’s experiment: Two type of strep. (1 with capsule “S” and 1 without “R”) S strain with capsule is deadly because…….? Heat killed S strain mixed with R strain can transform the R into S because of “transformation” http://www.youtube.com/watch ?v=hSbTWaR6Lzk
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Transduction New DNA is acquired via viral vector Virus injects the cell with its DNA DNA incorporates into host DNA When it is “cut out” it sometimes can pick up extra pieces. When the new virus infects the new DNA containing bacterial genes it creates variation. http://www.youtube.com/wa tch?v=oFMRnEnkr0g
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