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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