CHEE 229 Chapter 7
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Created by:
macgreb on February 9, 2011
Subjects:
microbial growth and reproduction
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28 terms
Terms | Definitions |
|---|---|
 Binary Fission | Procaryotic Cell cycle, occurs with most bacteria and archea |
| Step 1 of binary fission | Parent cell prepared for division by enlarging its cell wall, cell membrane and overall volume. |
| Step 2 of binary fission | Septum begins to grow inward as the chromosomes move toward opposite ends of the cell, other cytoplasmic components are distributed to the two developing cells |
| Step 3 of binary fission | Septum is synthesized completely through the cell center, and the cell membrane patches itself so that there are two separate cell chambers |
| Step 4 of binary fission | Daughter cells divide, some species separate completely while others remain attached, formed chains, doublets or other cellular arrangements |
| Cell growth | refers to population growth, not growth of individual cells |
| How cell growth is monitored | Increase in cell numbers, increase in cell mass |
| Phases in microbial growth in batch (closed) system | (1) Lag phase, (2) Exponential (log) phase, (3) Stationary phase, (4) Death phase |
| Lag phase (microbial growth closed system) | Cell synthesizing new components, varies in length (may be short or absent) |
| Exponential phase (microbial growth closed system) | Growth rate and division is constant and maximal, population most uniform in chemical and physical properties |
| Nutrient concentration vs yield graph | Mostly linear relationship, begins to plateau at high concentrations |
| Nutrient concentration vs growth rate graph | Steep rise, then plateaus (much sooner that yield graph) |
| Stationary phase (microbial growth closed system) | Total number of viable cells remains constant (may stop reproducing or rate balanced by death rate). Caused by nutrient limitation, limited oxygen, toxic waste accumulation |
| Death phase (microbial growth closed system) | Two possibilities: cell viable but not culturable (dormant) OR programmed cell death (commit suicide) |
| Specific growth rate formula | mu (specific growth) = (1/x)(dx/dt) |
| During exponential growth | doubling time = ln2/mu |
| Counting chambers | Easy, inexpensive, but cannot distinguish living from dead cells |
| Electronic counters | Good for large organisms/ blood cells - NOT procaryotes. Cell suspension is forced through small orifice, impacts electric current that flows through orifice, disruption of current counted electronically |
| Continuous culture | growth in an open system, maintains cells in log phase at a constant biomass concentration for extended periods of time, achieved using a continuous culture system |
| Dilution rate | rate at which medium flows through vessel relative to vessel size (flow/volume). At steady state D=mu |
| Measurement value vs. dilution rate graph | Nutrient concentration low than increases rapidly, cell density high than decreases rapidly |
| Hypotonic solution | Lower osmotic concentration outside cell. Water enters the cell, cell swells and may burst |
| Hypertonic solution | Higher osmotic concentration outside of cell, water leaves the cell and membrane shrinks from the cell wall |
| Water activity | Amount of water available to organisms, reduction by interaction with solute molecules (higher solute concentration = lower water activity) |
| Ionizing radiation | X-rays and gamma rays, causes DNA mutations leading to cell death, disrupts chemical structure of many molecules including DNA |
| Ultraviolet radiation | short wavelength and high energy, could lead to DNA death |
| biofilms | complex, slime enclosed communities of microbes. Initially attach reversible, but irreversible attached occurs with production of extracellular polymeric substances (EPS) |
| Quorum sensing | mediation by small proteins that increase in concentration as microbes replicate and convert microbe to competent sate |
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