Flashcards in lecture 6 Deck (30):
1
Periplasmic space
region between the plasma membrane and the cell wall. This area is loaded with enzymes
2
Enzymes
are present for catabolizing growth media into smaller sub-units. In addition, there are enzymes called restriction exonucleases. These are enzymes that will destroy foreign DNA.
3
penicillinase
Another enzyme, penicillinase may be found. Penicillinase hydrolyzes and thereby inactivates the antibiotic penicillin
4
Plasma membrane (cell membrane)
phospholipid bilayer with non-stationary proteins.
Described as the fluid mosaic model. The membrane serves as a site for selective permeability
5
Selective permeability of molecules moving through the plasma membrane is a function of the
following:
a. size and molecular weight
b. electric charge or polarity
c. lipid solubility
d. presence or lack of presence of enzymes called permeases
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In prokaryotes, ATP production
sites are located on the plasma membrane
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mesosomes
Electron micrographs depicted membranous intrusions of the bacterial plasma membrane. These were called mesosomes. Original theories considered these mesosomes to be structures associated with cell division or concentration of metabolic activity. Now they are considered to be artifacts of electron microscope preparation.
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Cytoplasmic contents
The nucleoid region
Plasmids
Ribosomes
RNA
Inclusions
Endospores
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The nucleoid region
contains a single, looped, circular ( no free ends) chromosome. This area comprises approximately 10% of the cell volume. It is free within the cell as it is not membrane bound. The DNA on the chromosome is organized into 2000 to 3000 genes
10
Plasmids
Plasmids are extrachomosomal loops of DNA that replicate independently of the chromosome
11
Ribosomes
Ribosomes are sites for protein synthesis. Thousands are present in a bacterial cell. They are made up of rRNA (ribosomal RNA) and protein.
12
RNA
Bacterial cells have the full complement of RNA. This includes m(messenger)RNA, t(transfer)RNA and r(ribosomal)RNA
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Inclusions
There are several kinds of inclusions or reserve deposits in prokaryote cells. These include:
volutin (metachromatic) granules
polysaccharide granules
lipid inclusions
sulfur granules
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volutin (metachromatic) granules
concentrations of polymetaphosphates. These are reserves of excess inorganic phosphates often times seen in older cells
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polysaccharide granules
-consist of glycogen and starch
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lipid inclusions
PHB (polyhydroxybutarate) is a common lipid storage material
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Endospores
Members of the genera Bacillus and Clostridium can form resistant, dormant, non-metabolizing forms of these cells called spores, during adverse conditions. This process is
called sporogenesis
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Spores
These spores are for protection and not reproduction. These structures are formed internally as endospores. Upon liberation, they are called free spores or just spores.
Spores as endospores or as free spores resist staining and display refractility. They contain low amounts of water and high amounts of calcium. They also contain high amounts of a substance known as dipicolinic acid (DPA) not to be confused with DAP, which is found in
peptidoglycan
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germination
Favorable conditions will restore theses cells to their vegetative forms. This process is called germination.
20
spore shapes
Spores have different shapes and different locations in varying species. When observing the endospore in Clostridium tetani, the endospore is swollen and terminally located.
This can help in identification. Sporulation has been used as one of the biological models to study the process of differentiation
21
Cell wall synthesis
When Gram positive cells divide, the new cell wall material is laid down at the septum, or area of cross wall formation. When Gram negative cells divide, the new cell wall growth is spread out in what is described as an intercalated pattern.
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Growth of Bacterial populations in liquid media
A. Lag Phase
B. Log Phase
C. Stationary Phase
D. Death ( Decline) Phase
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Lag Phase
1. This is a time of cellular adaptation. The bacterial cell is in its “physiologic youth.”
2. Cells are not dividing, yet they are extremely active. We observe the induction of
enzymes and the synthesis of precursor units.
3. Increases in cell metabolism and mass occur without cell division. Cell size increases
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Log Phase
1. Observed is exponential or geometric growth.
2. Division occurs at a constant and maximal rate.
3. These young cells are smaller in size and give the most consistent Gram stain. The best
time to Gram stain is therefore in the Log Phase.
4. The division is not synchronous. The population however, is dividing so often, the cells
are uniformly small in size.
5. Nutrients are still in excess and the cells are maximizing the utilization of the nutrients.
6. Natality is greater than mortality
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Stationary Phase
1. Natality is now equal to mortality.
2. The medium is now supporting the maximum concentration of cells.
3. Nutrients become limiting and are no longer in excess.
4. We see the appearance of granules, the accumulation of toxic wastes and the initiation
of sporogenesis during this phase.
5. Cell walls may start to weaken. Old Gram positive cells may now revert to Gram
negative.
6. Carbon dioxide levels may increase, and pH will decrease. Oxygen levels decline
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Death or Decline Phase
1. Mortality rates now exceed natality rates.
2. Death occurs at a constant and maximal rate. This geometric or exponential decline is
the reverse of the Log Phase.
3. We see the maximal activity of autolytic enzymes if present.
27
When examining a colony, the cells at the
periphery are those that are
in the Lag Phase
These are cells that are reaching out to new and unused
media.
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The layer of cells just interior to these cells would be in
the Log Phase
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Moving interiorly, we find the cells in the
Stationary Phase
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