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33 Cards in this Set
- Front
- Back
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What is meant by growth?
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Increase in cellular constituents that may result in:
-increase in cell number; when microorganisms reproduce by binary fission (most common meaning) -increase in cell size; coenoxytic microorgansism have nuclear divisions that are not accompanied by cell divisions (in some cases) Microbiologists usually study population growth rather than growth of individual cells. |
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What is meant by the cell cycle?
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Cell cycle is sequence of events from formation of new cell through the next cell division; most bacteria divide by binary fission.
Two pathways function during cycle; (1) DNA replication and partition (2) cytokinesis |
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Cell division
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Bacteria normally reproduce by binary fission in which a bacterium pinches into two cells that will grow to original size
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Origin of replication
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Site at which replication begins
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Terminus
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SIte at which replication is terminated
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Replisome
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Group of proteins needed for DNA synthesis; parent DNA spools through the replisome as replication occurs.
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MreB
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an actin homolog plays role in determination of cell shape
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General
DNA replication and cell division |
Takes 40 minutes to replicate the DNA. There is a 20 minute lag period between the end of a round of DNA replication and cell division. C=40 min. D=20 min. These are constants.
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If C and D are constants, what happens in the cell cycle if the generation time is 50 minutes?
Why is this an important concept? |
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Describe the role of MreB, FtsZ and the Z-ring in bacterial cell structure and division.
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Protein MreB
-similar to euk. actin. Plays a role in determination of cell shape and movement of chromosomes to opposite cell poles. Protein FtsZ -similar to euk. tubulin. Plays a role in Z ring formation which is essential for septation. (assembles in center to form Z ring) |
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Describe the four stages of the clasical growth curve.
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What are the major characteristics of each stage of the growth curve?
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Explain the difference between balanced growth and unbalanced growth.
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Growth Curve (general)
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Lag Phase
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Exponential Phase
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Balanced growth
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Unbalanced growth
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Unbalanced growth (diagram)
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Balanced growth (diagram)
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Effect of nutrient concentration on growth
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Stationary Phase
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What are some possible reasons for entry into stationary phase?
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-nutrient limitation
-limited oxygen availability -toxic waste accumulation -critical population density reached |
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Starvation responses
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Starvation is a recurring situation for bacteria in the natural environment.
-morphological changes -decrease in size, protoplase shrinkage, and nucleoid condensation -production of starvation proteins -long-term survival -increased virulence |
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Death Phase
Definition |
Cells always die at an exponential rate. Death:irreversible loss of ability to reproduce.
Do NOT die instantaneously! In some cases, death rate slows due to accumulation of resistant cells. |
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How do you determine the generation time of a bacterial culture?
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Generation (doubling) time
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Time required for the population to double in size
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Describe several ways to measure microbial growth
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-can measure changes in number of cells in a population
-can measure changes in mass of population |
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Measurement of cell numbers
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*Direct cell counts
-counting chambers -electronic counters (not imp) -on membrane filters *Viable cell counts -plating methods -membrane filtration methods |
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Advantages and disadvantages of the Petroff-Hausser counting chamber.
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Adv: easy, quick and inexpensive
Disadv: cannot distinguish living from dead cells and must have large numbers of cells to begin with |
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Petroff-Hausser counts
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N= number of cells/square
F= conversion factor= 10^7 cells/mL= N*F |
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Direct counts collected on a membrane filter
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-cells filtered through special membrane that provides dark background for observing cells. Cells are stained with fluorescent dyes. Useful for counting bacteria. With certain dyes, can distinguish living from dead cells (BacLight).
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Advantages and disadvantages of membrane filtration methods.
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Adv: can count organsims in dilute suspensions
Disadv: cost of materials |
