Exam 2 Notes

Exam 2 Notes - Exam 2 Microbiology Lab BACTERIAL GROWTH:...

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Exam 2 Microbiology Lab BACTERIAL GROWTH: -Bacteria reproduces asexually (1 mother cell gives rise to 2 daughter cells) - Binary Fission -Entails an increase in cell size, a duplication of the entire chromosome, synthesis of new cell wall and plasma membrane, and finally division -This process causes a change in both cell number and cell mass -When conditions are favorable, bacteria growth is exponential, a sigmoidal curve, in particular EXPONENTIAL GROWTH CURVE PHASES (1) Lag (2) Log (3) Stationary (4) Death (1) LAG PHASE: -Freshly inoculates cells grow accustom to their surroundings, needing to become accustom to: -pH -Salts -Nutrients -Oxygen Levels -Light -Temperature (2) LOG/EXPONENTIAL PHASE: -The bacteria begin dividing on a fairly normal schedule (generation time) based on the species and media -As a result, cell counts jump rapidly in a short period of time due to the doubling of the population EX: 2(0), 2(1), 2(2), 2(3)…. .2(n) N=Generation Time (3) STATIONARY PHASE: -The cells are at their max growth potential, limited by: -Nutrient concentrations being too low -Metabolic products which are inhibitory to the cell -Flat out run out of space (Too densely packed) -While the cell numbers remain the same, this is NOT A STATIC PHASE -Cells are continuously growing up to a point and then stopping -The population keeps moving (4) DEATH PHASE: -The population of cells declines
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WHAT AND HOW DO WE COUNT? Cell Numbers: How? -Microscopic Counts (<10(7) -Electronic Counts (a la robots like Rosie or Wall-E) -Viable Counts- Dilution series of a culture Cell Mass: How? -Physical Measures- Weight, Volume -Chemical Measures- Atomic methods, Protein/DNA Counts -Chemical Activity Measures-Gas Consumption/Production -Turbidity Measures-Optical Density TURBIDITY: -Turbidity Measurements and Viability Counts are very common -They are also experiments 18 &19 -Turbidity is the term used for inoculated broth cultures with growth -When there is growth, the culture becomes cloudy, or foggy looking. This can be given a quantitative number by using UV spectroscopy SPECTROPHOTOMETER: -Measures an objects absorbance (A) of light from source, as well as its transmittance (%T) of that light ISSUES W/ SPECTROPHOTOMETERS: -Since dead cells refract as well, it is difficult to see the Death Phase -The machines can be finicky -Physics gets in the way (Limits to linear lines vs. concentration) -What to do? Viable Counts and Serial Dilutions VIABLE COUNTS: -Use a broth culture which is serially diluted and plated on media to grow. -The amount of colonies which grow are directly related to the amount of bacteria present
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This note was uploaded on 04/23/2009 for the course BIO 201 taught by Professor Paquette during the Spring '09 term at Rhode Island.

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Exam 2 Notes - Exam 2 Microbiology Lab BACTERIAL GROWTH:...

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