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Bacterial Cell Structure & Growth: Periplasm, Membrane, Cytoplasm, Growth Phases, Study notes of Microbiology

An in-depth exploration of the periplasmic space, plasma membrane, and cytoplasmic contents of bacterial cells. It also covers the growth phases of bacterial populations in both liquid media and solid colonies, including the lag phase, log phase, stationary phase, and death or decline phase.

Typology: Study notes

2011/2012

Uploaded on 12/23/2012

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6. Periplasmic space-region between the plasma membrane and the cell wall. This area is loaded
with enzymes. 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. Another enzyme, penicillinase may be found. Penicillinase hydrolyzes
and thereby inactivates the antibiotic penicillin.
7. 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.
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
The plasma membrane serves as a site for chemical reactions. In prokaryotes, ATP production
sites are located on the plasma membrane. 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.
8. Cytoplasmic contents
a. 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.
b. Plasmids are extrachomosomal loops of DNA that replicate independently of the
chromosome.
c. Ribosomes are sites for protein synthesis. Thousands are present in a bacterial cell. They are
made up of rRNA (ribosomal RNA) and protein.
d. RNA-Bacterial cells have the full complement of RNA. This includes m(messenger)RNA,
t(transfer)RNA and r(ribosomal)RNA.
e. Inclusions- There are several kinds of inclusions or reserve deposits in prokaryote cells. These
include:
1. volutin (metachromatic) granules-concentrations of polymetaphosphates. These are
reserves of excess inorganic phosphates often times seen in older cells.
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  1. Periplasmic space-region between the plasma membrane and the cell wall. This area is loaded with enzymes. 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. Another enzyme, penicillinase may be found. Penicillinase hydrolyzes and thereby inactivates the antibiotic penicillin.
  2. 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. 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

The plasma membrane serves as a site for chemical reactions. In prokaryotes, ATP production sites are located on the plasma membrane. 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.

  1. Cytoplasmic contents

a. 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.

b. Plasmids are extrachomosomal loops of DNA that replicate independently of the chromosome.

c. Ribosomes are sites for protein synthesis. Thousands are present in a bacterial cell. They are made up of rRNA (ribosomal RNA) and protein.

d. RNA-Bacterial cells have the full complement of RNA. This includes m(messenger)RNA, t(transfer)RNA and r(ribosomal)RNA.

e. Inclusions- There are several kinds of inclusions or reserve deposits in prokaryote cells. These include:

  1. volutin (metachromatic) granules-concentrations of polymetaphosphates. These are reserves of excess inorganic phosphates often times seen in older cells.
  1. polysaccharide granules-consist of glycogen and starch.
  2. lipid inclusions- PHB (polyhydroxybutarate) is a common lipid storage material.
  3. sulfur granules

f. 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. 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. Favorable conditions will restore theses cells to their vegetative forms. This process is called germination. 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. 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.

Microbial Growth (Ch. 6)

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.

Growth of Bacterial populations in liquid media-learn the four phases of the bacterial growth curve. They are:

A. Lag Phase

B. Log Phase

C. Stationary Phase

D. Death ( Decline) Phase

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.

The above mentioned growth phases are described with cells in a liquid medium. These phases can be described when a colony is growing on a solid medium. 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. The layer of cells just interior to these cells would be in the Log Phase. Moving interiorly, we find the cells in the Stationary Phase. Those cells at the very middle of the colony would be in the Death or Decline Phase.