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The growth of individual cells is what? Why?
exponential,because of autocatalytic nature; the production of ribosomes and enzymes allows for the production of even more ribsomes and enzymes.
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Topic: Growth and Division of Individual Cells
How do most procaryotes divide?
by binary fission
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Describe how binary fission works in this case?
- -Cells split by septum; FtsZ protein ring pulls membrane in
- -New orientation of membrane reorients peptidoglycan synthesis
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Some cells divide by what two processes?
budding or multiple fission
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Define budding.
small daughter cells forms and continues to increase in size until they are size of mother cell; some bud at the end of hypha (Hyphomicrobium)
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Define Multiple Fission
mother cell increases to large size and then has multiple divisions; seen in some mycelial organisms which then form chains of spores
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Why are the interdivision times of individual cells are quite variable?
Because interdivision can vary in length, many cells in a culture can be at different stage; synchronized cells are necessary for many studies
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What did Helmstetter and Cooper develope?
“baby machine” method of getting synchronous cells
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Why can Procaryotic growth rates can be highly variable?
Because of highly variable interdivision time, generally only measure average interdivision and report growth as generation time
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What are the Procaryotic growth rates?
Growth rates can vary over a 10-fold range (E. coli in rich medium [20 minutes], in minimal medium [1.5 hours]
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Procaryotic chromosomes replicate bidirectionally from where?
A single origin
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In regards to origin what is specific about Eukarya and archaea?
they have multiple origins of replication
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Define Origin
is a region with special sequences that bind initiation protein (DnaA); two replisomes form; replication continues to terminus
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Segregation of the bacterial chromosome is mediated by what?
the bacterial cytoskeleton (in eukaryotes, mitosis is a separate process)
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In procaryotes, successive cell cycles can do what?
overlap
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C period
(equivalent to S phase of eukaryotes) – amount of time it takes for the bacterial chromosome to be replicated (40 minutes in E. coli)
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D period
(equivalent to the eukaryotic G1 phase) – time between replications; present in bacteria with generation time of more than 1 hour but disappears at higher growth rates (20 minutes)
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In cells that divide faster than 60 minutes, next DNA replication must begin when?
before previous division is complete
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Topic: Microbial Population Growth
How is Microbial population growth is normally measured?
spectrophotometry
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Within limits, the amount of light scattering (optical density or absorbance) is strictly proportional to what?
the amount of biomass present in suspension
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Principle limitations of technique are that?
it is not sensitive enough for small concentrations of cells and does not differentiate between living and dead cells
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Microbial population growth is?
exponential
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When do populations enter stationary phase?
when they run out of nutrients or accumulate toxic quantities of waste materials
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When does Exponential growth stop?
when nutrients drop/waste accumulates and stationary phase begin
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In stationary phase what happens?
DNA replication stops, and cell becomes more resistant to environmental stress
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What is it called when cells have been in exponential growth for several generations?
balanced growth
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Define Lag phase
period of adjustment that cells when cells are placed into a new medium/environment
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Why is it difficult to do experiments at the beginning of log/beginning of stationary, cells are adjusting?
because cells are not physiologically the same; experiments are done on cells in between (balanced growth)
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Maintenance metabolism is necessary for cells in what phase? What 4 ways is this accomplished?
- stationary phase
- -Permeases must remain active to maintain normal concentrations of solutes
- -DNA repair mechanisms must remain active
- -Motility, particularly in starving conditions must be maintained
- -These require maintenance energy, less than required for active growth
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Microbial death is?
exponential
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A subpopulation of stationary phase cells can survive for how long?
months
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Growth at low nutrient concentrations is studied in whats called?
the chemostat
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Define Batch culture
microbes go through entire life cycle (like in a flask)
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Define Continuous culture
adding nutrients and removing waste at a constant rate so as to keep cells in balanced growth (must be done at the correct rate so cells do not enter stationary phase OR get diluted out)
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Growth in nature is usually continuous like what other two things? In Aquatic environments? In soil?
- like a chemostat, or episodic like successive batch cultures
- -As in aquatic environments, growth is like a chemostat where nutrients are constantly supplied
- -In soil habitats, growth is like batch culture since nutrients are added periodically
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Topic: The Effect of Environmental Conditions on Growth
Each strain is characterized by a set of 3 cardinal temperatures, what are they?
Minimum, optimum, maximum
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Cold may cause what in the cell?
multiple failures in cell (proteins do not have sufficient thermal energy to fold into required conformation, this interferes with protein, nucleic acid synthesis; membranes become less fluid, decreasing diffusion)
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What are maximum temps and maximal temps set by?
Maximum temps set by stability of proteins and maximal temp at which 3D structure is stable
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Collectively, procaryotes grow over the entire range of temperature from what to what?
- –10°C to about 120°C
- ex:Psychrophiles, mesophiles, thermophiles, hyperthermophiles
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What is the highest recorded optimum temp?
Highest recorded optimum is 113oC although Pyrolobus fumarii may have optimum of 115oC and maximum of 121oC
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Procaryotes grow over a range of what values?
- pH values, while maintaining constant internal pH
- ex: Acidophiles, neutrophiles, alkaliphiles
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Alkaliphiles have particular problem of maintaining what?
different cytoplasmic chemistry than environment; use sodium pumps to great membrane gradients rather than just protons
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Osmoregulation in procaryotes involves the synthesis or uptake of what?
solutes to keep the cytosol more concentrated than the environment
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Procaryotes rely on what?
high internal solute concentrations for growth and division (cells swell)
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Many use compatible solutes (not just NaCl in cytoplasm);
K+ in E.coli, glutamate in gram negatives, proline in gram positives
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Aerobic growth requires several protections against the toxic effects of oxygen. What are they? (6)
-Oxygen can form various toxic, powerful oxidizing agents (singlet oxygen [1O2], superoxide [O2–‑], hydrogen peroxide [H2O2])
-Evolutionary biologists believe there was a great wave of extinction when oxygen first started to appear
-Carotenoid pigments protect against singlet oxygen (which is formed in light)
-Superoxide dismutase catalyzes 2 O2–‑ + 2 H+ à H2O2 + O2
-Catalase catalyzes 2 H2O2 à H2O + O2
-Peroxidase catalyzes NADH + H+ + H2O2 à 2 H2O + NAD+
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