Microbial Growth

Microbial Growth - Microbial Growth Chapter 6(6.1-6.16(In microbiology growth is defined as an increase in cell number The bacterial population is

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Microbial Growth- Chapter 6 (6.1-6.16) (In microbiology growth is defined as an increase in cell number: “The bacterial population is growing in number.”) Cell division in prokaryotes Called _Binary Fission ____ See figure 6.1 for steps Note that cell division in prokaryotes is much simpler than in eukaryotes. Cell division in eukaryotes (mitosis) must also involve accurate division of all the separate chromosomes. Fts Proteins and Cell Division Series of proteins found in prokaryotes that interact to form divisome Some of these proteins include: FtsZ: (first step) forms a ring in the middle of a cell (once DNA replication is over) FtsA: hydrolyzes ATP for energy FtsI: involved in new peptidoglycan synthesis FtsK: involved in pulling apart DNA molecules Figure 6.2a Arrangement of divisome proteins How are cell shapes determined? NOT by arrangement of peptidoglycan MreB protein Forms actin-like filament Different arrangements = different shapes Coccus-shaped bacteria lack gene for MreB Spherical is “default”
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Peptidoglycan Synthesis and Cell Division Openings in existing wall created at FtsZ ring by autolysins Precursors transported by bactopreno l Transpeptidation Formation of peptide bond cross-links Target of penicillin Population growth “population” because we refer to the growth of a population of microorganisms, not the growth of a single organism Some definitions: Growth rate: change in cell number per unit time Generation time: time required for one round of cell division (a generation), doubling time (depends on species/genetics and environment) - Prokaryotes typically faster than eukaryotes Exponential growth – total cell number of population doubles each unit time See figure 6.6a for an example of exponential growth. Note that the number of cells in the population is doubling every 30 minutes. The growth rate continuously increases in exponential growth. For example, in the 30 minute span from 1 to 1.5 hours the cell population increased by 4. In the 30 minute span from 5 to 5.5 hours, the population increased by 1,024. Also see figure 6.7b for a plot of exponential growth. Note that from this graph you can determine the generation time (time it takes to double). The cell number doubles when it changes from 3 x 10 7 to 6 x 10 7 . How much time did it take for the culture to go from 3 x 10 7 cells/ml to 6 x 10 7 ? That is the doubling time. Calculations of growth N=N o 2 n g=t/n N= final number N o = initial number n= number of generations t= hours or minutes of exponential growth g= generation time
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Sample problem: Escherichia coli has a generation time of 20 minutes, it has been growing exponentially for 3 hours, and this culture was initially started with 5 E. coli cells. How many generations have occurred in the 3 hours?
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This note was uploaded on 10/01/2008 for the course BIOL 2051 taught by Professor Brininstool during the Fall '07 term at LSU.

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Microbial Growth - Microbial Growth Chapter 6(6.1-6.16(In microbiology growth is defined as an increase in cell number The bacterial population is

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