Notes 10

Notes from today's lecture :)


October 5, 2009

I. Phases of bacterial growth curve (in culture … not in nature) – Assuming you have a pure culture of bacteria (drawing on hand out)
a. Lag phase -
i. Takes a while to go from having few bacteria to a lot
ii. Bacterial cell division getting started
iii. Generation times not as rapid as will be during exponential phase (b)
iv. Bacteria are making:
1. ATP
2. Cell envelope components
3. Enzymes like DNA polymerase, FtsZ…
4. Before they can begin dividing rapidly these things need to be made so they have them
b. Exponential phase – (Log Phase)
i. **During this phase generation time is shortest; nutrients are abundant
1. So bacteria easily able to make all components needed for division
ii. Lasts ‘forever’ … It goes on for a long time before moving onto the stationary phase (c)
c. Stationary phase –
i. *In this phase growth has stopped
ii. Number of deaths is equal to the number of new bacteria
iii. Bacteria are running out of nutrients → so the bacteria are much less able to produce all of the components that they need in order to survive → because of the lack of food some bacteria are starting to just die off
d. Death phase –
i. Number of new bacteria is vastly outnumbered by our number of dying bacteria
ii. Almost completely out of food so the cell division has essentially come to a complete stop → lack of food = death
iii. Bacterial cell suicide – common at high population densities
1. Each bacterium has receptors on the outside of the cell, and each cell is giving out signaling molecules.
2. When the population is very high and there is no where for the signaling molecule to go it will stick to it’s own cells receptors → when all of the cells receptors are full the cell takes that as a sign that it is time to kill itself
II. Generation time = 0.301(t-t0)/(log10N-log10N0)

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