Biomedical Engineering Reference
In-Depth Information
TABLE 2.3 Characteristics of Various Components of Bacteria
Part
Size
Composition and comments
SLIME LAYER
Microcapsule
5 e 10 nm
Protein e polysaccharide e lipid complex responsible for the
specific antigens of enteric bacteria and other species.
Capsule
0.5 e 2.0 m m
Mainly polysaccharides (e.g. Streptococcus); sometimes
polypeptides (e.g. Bacillus anthracis).
Slime
Indefinite
Mainly polysaccharides (e.g. Leuconostoc); sometimes
polypeptides (e.g. Bacillus subtilis).
CELL WALL
Gram-positive species
10 e 20 nm
Confers shape and rigidity upon the cell. 20% dry weight of
the cell. Consists mainly of macromolecules of a mixed
polymer of N-acetyl muramic peptide, teichoic acids, and
polysaccharides.
Gram-negative species
10 e 20 nm
Consists mostly of a protein e polysaccharide e lipid
complex with a small amount of the muramic polymer.
Cell membrane
5 e 10 nm
Semipermeable barrier to nutrients. 5 e 10% dry weight of
the cell, consisting of 50% protein, 28% lipid, and 15 e 20%
carbohydrate in a double-layered membrane.
10 e 20 nm by 4 e 12 m m
Protein of the myosin e keratin e fibrinogen class, MW of
40,000. Arises from the cell membrane and is responsible for
motility.
Flagellum
Pilus (fimbria)
5 e 10 nm by 0.5 e 2.0 m m
Rigid protein projections from the cell. Especially long ones
are formed by Escherichia coli.
INCLUSIONS
Spore
1.0 e 1.5 m m by 1.6 e 2.0 m m One spore is formed per cell intracellularly. Spores show
great resistance to heat, dryness, and antibacterial agents.
Storage granule
0.5 e 2.0 m m
Glycogen like, sulfur, or lipid granules may be found in
some species.
50 e 100 nm
Chromatophore
Organelles in photosynthetic species. Rhodospirillum rubrum
contains about 6000 per cell.
Ribosome
10 e 30 nm
Organelles for synthesis of protein. About 10,000 ribosomes
per cell. They contain 63% RNA and 37% protein.
Volutin
0.5 e 1.0 m m
Inorganic polymetaphosphates that stain
metachromatically.
Nuclear material
Composed of DNA that functions genetically as if the genes
were arranged linearly on a single endless chromosome but
that appears by light microscopy as irregular patches with
no nuclear membrane or distinguishable chromosomes.
Autoradiography confirms the linear arrangement of DNA
and suggests an MW of at least 10 9 .
Source: S. Aiba, A. E. Humphrey, and N. F. Millis, Biochemical Engineering, 2d ed., University of Tokyo Press, Tokyo, 1973.
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