Lecture 2.10 Notes

Lecture 2.10 Notes - Notes, lecture 8, BIOL401 2/10/10...

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Notes, lecture 8, BIOL401 – 2/10/10 Growth of Bacterial Populations Length of time it takes for the formation of 2 cells from 1 generation time ( doubling time) Generation time can vary widely among different types of bacteria Dependent on growth conditions Exponential Growth: n N N 2 0 = where n = number of doublings N = number of bacteria after n doublings N 0 = starting number of bacteria ) log (log 3 . 3 301 . 0 log log 2 log log log 2 log log log 2 0 0 0 0 0 N N N N n n N N n N N N N n - = - = = - + = = Determination of growth parameters: Semilogarithmic graph of Cell# vs Time yields straight line during exponential growth (since cells double in a constant period of time) o Such graphs can be used to estimate doubling times (see Fig 6.7) Related Growth Parameters Generation Time ( a.k.a. - doubling time ): time required for cell population to double time/doubling also time needed for single cell to divide by binary fission g=t/n, also, g = 0.301/slope Division Rate: # of generations per unit time v = 1/g, where g = generation time Specific Growth Rate : k = 0.301 n/t, where n= # of doublings, and, t = time note that n/t = 1/g so k=0.301/g g = 0.301/ k Generation time is also equal to 0.301/slope as described below: For cells that are in the exponential phase of growth, we can plot the number of cells per ml vs time on a semilog graph and we observe a straight line.
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The slope of a straight line is defined as: X Y slope = By definition, when Δ X = g (generation, or, doubling time), Δ Y = 2 However, we only get a straight line when we plot the number of cells/ml vs time on semilog paper ( i.e. when we are actually plotting time vs the log of the # of cells per ml). Therefore the linear relationship holds, when Δ X = g, and, Δ Y = log 2 So, k g g X Y slope = = = = 301 . 0 2 log ( specific growth rate) Given g slope 301 . 0 = we can multiply both sides of the equation by slope g to obtain: slope g 301 . 0 = The Growth Cycle Batch culture – closed system lag phase – cells adjust to new conditions; length variable depending on history of culture and growth conditions exponential phase – cells in healthiest state, rate influenced by environmental conditions stationary phase – exponential growth limited in batch culture, growth limited by variety of factors including, depletion of essential nutrient(s) and accumulation of waste products
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Lecture 2.10 Notes - Notes, lecture 8, BIOL401 2/10/10...

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