Environmental Engineering Reference
In-Depth Information
Nucleoid (Nuclear Body or Region)
The
nuclear region
of the procaryotic cell is primitive and a striking contrast
to that of the eucaryotic cell. Procaryotic cells lack a distinct nucleus; instead,
the function of the nucleus is carried out by a single, long, double strand of
deoxyribonucleic acid (DNA) that is efficiently packaged to fit within the
nucleoid. The nucleoid is attached to the plasma membrane. A cell can have
more than one nucleoid when cell division occurs after the genetic material
has been duplicated.
Ribosomes
The bacterial cytoplasm is often packed with
ribosomes
, which are minute,
rounded bodies made of ribonucleic acid (RNA) that are loosely attached to
the plasma membrane. Ribosomes are estimated to account for about 40%
of the dry weight of a bacterium; a single cell may have as many as 10,000
ribosomes. Ribosomes are the site of protein synthesis and are part of the
translation process; they are commonly called the “powerhouses of the cell.”
Inclusions
Inclusions
(or storage granules) are often seen within bacterial cells. Some
inclusion bodies are not bound by a membrane and lie free in the cytoplasm.
Other inclusion bodies are enclosed by a single-layer membrane about 2 to
4 µm thick. Many bacteria produce polymers that are stored as granules in
the cytoplasm.
DID YoU KNoW?
The human body consists of millions of different cells. A bacterium
consists of a single cell.
Chemical Composition of a bacterial Cell
Bacteria, in general, are composed primarily of water (about 80%) and of dry
matter (about 20%). The dry matter consists of both organic (90%) and inor-
ganic (10%) components. All basic elements from protoplasm must be derived
from the liquid environment, and if the environment is deficient in vital ele-
ments the cell shows a characteristic lack of development.
Note:
The normal growth of a bacterial cell in excess nutrients results in
a cell of definite chemical composition. The growth, however, involves
a coordinated increase in the mass of its constituent parts, not solely an
increase in total mass.
