do bacteria have cytoplasm ?
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Joe J. Sander
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The cytoplasm has two distinct areas when seen in the
electron microscope:
(1) An amorphous matrix that contains ribosomes,
nutrient granules, metabolites, and plasmids.
(2) An inner, nucleoid region composed of DNA.
Ribosomes
Bacterial ribosomes are the site of protein synthesis as in eukaryotic cells, but they differ from eukaryotic ribosomes
in size and chemical composition.Bacterial ribosomes are
70S in size, with 50S and 30S subunits, whereas eukaryotic
ribosomes are 80S in size, with 60S and 40S subunits. The
differences in both the ribosomal RNAs and proteins con-
stitute the basis of the selective action of several antibiotics
that inhibit bacterial, but not human, protein synthesis.
Granules
The cytoplasm contains several different types of granules that serve as storage areas for nutrients and stain character-
istically with certain dyes. For example, volutin is a reserve of
high energy stored in the form of polymerized metaphosphate. It appears as a “metachromatic” granule since it stains
red with methylene blue dye instead of blue as one would
expect. Metachromatic granules are a characteristic feature
of Corynebacterium diphtheriae, the cause of diphtheria.
Nucleoid
The nucleoid is the area of the cytoplasm in which DNA is
located. The DNA of prokaryotes is a single, circular molecule that has a molecular weight (MW) of approximately 2 × 109
and contains about 2000 genes. (By contrast, human DNA has approximately 100,000 genes.) Because the nucleoid contains no nuclear membrane, no nucleolus, no mitotic spindle, and no histones, there is little resemblance to the eukaryotic nucleus. One major difference between bacterial DNA and eukaryotic DNA is that bacterial DNA has no introns, whereas eukaryotic DNA does.