MICRO EXAM 2
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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.
Topic: Growth and Division of Individual Cells
How do most procaryotes divide?
by binary fission
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
Some cells divide by what two processes?
budding or multiple fission
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)
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
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
What did Helmstetter and Cooper develope?
“baby machine” method of getting synchronous cells
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
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]
Procaryotic chromosomes replicate bidirectionally from where?
A single origin
In regards to origin what is specific about Eukarya and archaea?
they have multiple origins of replication
is a region with special sequences that bind initiation protein (DnaA); two replisomes form; replication continues to terminus
Segregation of the bacterial chromosome is mediated by what?
the bacterial cytoskeleton (in eukaryotes, mitosis is a separate process)
In procaryotes, successive cell cycles can do what?
(equivalent to S phase of eukaryotes) – amount of time it takes for the bacterial chromosome to be replicated (40 minutes in E. coli)
(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)
In cells that divide faster than 60 minutes, next DNA replication must begin when?
before previous division is complete
Topic: Microbial Population Growth
How is Microbial population growth is normally measured?
Within limits, the amount of light scattering (optical density or absorbance) is strictly proportional to what?
the amount of biomass present in suspension
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
Microbial population growth is?
When do populations enter stationary phase?
when they run out of nutrients or accumulate toxic quantities of waste materials
When does Exponential growth stop?
when nutrients drop/waste accumulates and stationary phase begin
In stationary phase what happens?
DNA replication stops, and cell becomes more resistant to environmental stress
What is it called when cells have been in exponential growth for several generations?
Define Lag phase
period of adjustment that cells when cells are placed into a new medium/environment
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)
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
Microbial death is?
A subpopulation of stationary phase cells can survive for how long?
Growth at low nutrient concentrations is studied in whats called?
Define Batch culture
microbes go through entire life cycle (like in a flask)
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)
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
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
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)
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
Collectively, procaryotes grow over the entire range of temperature from what to what?
- –10°C to about 120°C
- ex:Psychrophiles, mesophiles, thermophiles, hyperthermophiles
What is the highest recorded optimum temp?
Highest recorded optimum is 113oC although Pyrolobus fumarii may have optimum of 115oC and maximum of 121oC
Procaryotes grow over a range of what values?
- pH values, while maintaining constant internal pH
- ex: Acidophiles, neutrophiles, alkaliphiles
Alkaliphiles have particular problem of maintaining what?
different cytoplasmic chemistry than environment; use sodium pumps to great membrane gradients rather than just protons
Osmoregulation in procaryotes involves the synthesis or uptake of what?
solutes to keep the cytosol more concentrated than the environment
Procaryotes rely on what?
high internal solute concentrations for growth and division (cells swell)
Many use compatible solutes (not just NaCl in cytoplasm);
K+ in E.coli, glutamate in gram negatives, proline in gram positives
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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